14 Nov, 2014
2 commits
-
Several people have reported occasionally seeing processes stuck in
compact_zone(), even triggering soft lockups, in 3.18-rc2+.Testing a revert of commit e14c720efdd7 ("mm, compaction: remember
position within pageblock in free pages scanner") fixed the issue,
although the stuck processes do not appear to involve the free scanner.Finally, by code inspection, the bug was found in isolate_migratepages()
which uses a slightly different condition to detect if the migration and
free scanners have met, than compact_finished(). That has not been a
problem until commit e14c720efdd7 allowed the free scanner position
between individual invocations to be in the middle of a pageblock.In a relatively rare case, the migration scanner position can end up at
the beginning of a pageblock, with the free scanner position in the
middle of the same pageblock. If it's the migration scanner's turn,
isolate_migratepages() exits immediately (without updating the
position), while compact_finished() decides to continue compaction,
resulting in a potentially infinite loop. The system can recover only
if another process creates enough high-order pages to make the watermark
checks in compact_finished() pass.This patch fixes the immediate problem by bumping the migration
scanner's position to meet the free scanner in isolate_migratepages(),
when both are within the same pageblock. This causes compact_finished()
to terminate properly. A more robust check in compact_finished() is
planned as a cleanup for better future maintainability.Fixes: e14c720efdd73 ("mm, compaction: remember position within pageblock in free pages scanner)
Signed-off-by: Vlastimil Babka
Reported-by: P. Christeas
Tested-by: P. Christeas
Link: http://marc.info/?l=linux-mm&m=141508604232522&w=2
Reported-by: Norbert Preining
Tested-by: Norbert Preining
Link: https://lkml.org/lkml/2014/11/4/904
Reported-by: Pavel Machek
Link: https://lkml.org/lkml/2014/11/7/164
Cc: Joonsoo Kim
Cc: David Rientjes
Cc: Mel Gorman
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
Commit 7d49d8868336 ("mm, compaction: reduce zone checking frequency in
the migration scanner") has a side-effect that changes the iteration
range calculation. Before the change, block_end_pfn is calculated using
start_pfn, but now it blindly adds pageblock_nr_pages to the previous
value.This causes the problem that isolation_start_pfn is larger than
block_end_pfn when we isolate the page with more than pageblock order.
In this case, isolation would fail due to an invalid range parameter.To prevent this, this patch implements skipping the range until a proper
target pageblock is met. Without this patch, CMA with more than
pageblock order always fails but with this patch it will succeed.Signed-off-by: Joonsoo Kim
Cc: Vlastimil Babka
Cc: Minchan Kim
Cc: Michal Nazarewicz
Cc: Naoya Horiguchi
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds
30 Oct, 2014
1 commit
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Commit edc2ca612496 ("mm, compaction: move pageblock checks up from
isolate_migratepages_range()") commonizes isolate_migratepages variants
and make them use isolate_migratepages_block().isolate_migratepages_block() could stop the execution when enough pages
are isolated, but, there is no code in isolate_migratepages_range() to
handle this case. In the result, even if isolate_migratepages_block()
returns prematurely without checking all pages in the range,isolate_migratepages_block() is called repeately on the following
pageblock and some pages in the previous range are skipped to check.
Then, CMA is failed frequently due to this fact.To fix this problem, this patch let isolate_migratepages_range() know
the situation that enough pages are isolated and stop the isolation in
that case.Note that isolate_migratepages() has no such problem, because, it always
stops the isolation after just one call of isolate_migratepages_block().Signed-off-by: Joonsoo Kim
Acked-by: Vlastimil Babka
Cc: David Rientjes
Cc: Minchan Kim
Cc: Michal Nazarewicz
Cc: Naoya Horiguchi
Cc: Christoph Lameter
Cc: Rik van Riel
Cc: Mel Gorman
Cc: Zhang Yanfei
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds
10 Oct, 2014
13 commits
-
Sasha Levin reported KASAN splash inside isolate_migratepages_range().
Problem is in the function __is_movable_balloon_page() which tests
AS_BALLOON_MAP in page->mapping->flags. This function has no protection
against anonymous pages. As result it tried to check address space flags
inside struct anon_vma.Further investigation shows more problems in current implementation:
* Special branch in __unmap_and_move() never works:
balloon_page_movable() checks page flags and page_count. In
__unmap_and_move() page is locked, reference counter is elevated, thus
balloon_page_movable() always fails. As a result execution goes to the
normal migration path. virtballoon_migratepage() returns
MIGRATEPAGE_BALLOON_SUCCESS instead of MIGRATEPAGE_SUCCESS,
move_to_new_page() thinks this is an error code and assigns
newpage->mapping to NULL. Newly migrated page lose connectivity with
balloon an all ability for further migration.* lru_lock erroneously required in isolate_migratepages_range() for
isolation ballooned page. This function releases lru_lock periodically,
this makes migration mostly impossible for some pages.* balloon_page_dequeue have a tight race with balloon_page_isolate:
balloon_page_isolate could be executed in parallel with dequeue between
picking page from list and locking page_lock. Race is rare because they
use trylock_page() for locking.This patch fixes all of them.
Instead of fake mapping with special flag this patch uses special state of
page->_mapcount: PAGE_BALLOON_MAPCOUNT_VALUE = -256. Buddy allocator uses
PAGE_BUDDY_MAPCOUNT_VALUE = -128 for similar purpose. Storing mark
directly in struct page makes everything safer and easier.PagePrivate is used to mark pages present in page list (i.e. not
isolated, like PageLRU for normal pages). It replaces special rules for
reference counter and makes balloon migration similar to migration of
normal pages. This flag is protected by page_lock together with link to
the balloon device.Signed-off-by: Konstantin Khlebnikov
Reported-by: Sasha Levin
Link: http://lkml.kernel.org/p/53E6CEAA.9020105@oracle.com
Cc: Rafael Aquini
Cc: Andrey Ryabinin
Cc: [3.8+]
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
C mm/compaction.o
mm/compaction.c: In function isolate_freepages_block:
mm/compaction.c:364:37: warning: flags may be used uninitialized in this function [-Wmaybe-uninitialized]
&& compact_unlock_should_abort(&cc->zone->lock, flags,
^Signed-off-by: Xiubo Li
Cc: Vlastimil Babka
Cc: Mel Gorman
Cc: David Rientjes
Cc: Minchan Kim
Cc: Arnd Bergmann
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
struct compact_control currently converts the gfp mask to a migratetype,
but we need the entire gfp mask in a follow-up patch.Pass the entire gfp mask as part of struct compact_control.
Signed-off-by: David Rientjes
Signed-off-by: Vlastimil Babka
Reviewed-by: Zhang Yanfei
Acked-by: Minchan Kim
Acked-by: Mel Gorman
Cc: Joonsoo Kim
Cc: Michal Nazarewicz
Cc: Naoya Horiguchi
Cc: Christoph Lameter
Cc: Rik van Riel
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
The page allocator has gfp flags (like __GFP_WAIT) and alloc flags (like
ALLOC_CPUSET) that have separate semantics.The function allocflags_to_migratetype() actually takes gfp flags, not
alloc flags, and returns a migratetype. Rename it to
gfpflags_to_migratetype().Signed-off-by: David Rientjes
Signed-off-by: Vlastimil Babka
Reviewed-by: Zhang Yanfei
Reviewed-by: Naoya Horiguchi
Acked-by: Minchan Kim
Acked-by: Mel Gorman
Cc: Joonsoo Kim
Cc: Michal Nazarewicz
Cc: Christoph Lameter
Cc: Rik van Riel
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
The migration scanner skips PageBuddy pages, but does not consider their
order as checking page_order() is generally unsafe without holding the
zone->lock, and acquiring the lock just for the check wouldn't be a good
tradeoff.Still, this could avoid some iterations over the rest of the buddy page,
and if we are careful, the race window between PageBuddy() check and
page_order() is small, and the worst thing that can happen is that we skip
too much and miss some isolation candidates. This is not that bad, as
compaction can already fail for many other reasons like parallel
allocations, and those have much larger race window.This patch therefore makes the migration scanner obtain the buddy page
order and use it to skip the whole buddy page, if the order appears to be
in the valid range.It's important that the page_order() is read only once, so that the value
used in the checks and in the pfn calculation is the same. But in theory
the compiler can replace the local variable by multiple inlines of
page_order(). Therefore, the patch introduces page_order_unsafe() that
uses ACCESS_ONCE to prevent this.Testing with stress-highalloc from mmtests shows a 15% reduction in number
of pages scanned by migration scanner. The reduction is >60% with
__GFP_NO_KSWAPD allocations, along with success rates better by few
percent.Signed-off-by: Vlastimil Babka
Reviewed-by: Zhang Yanfei
Acked-by: Minchan Kim
Acked-by: Mel Gorman
Cc: Joonsoo Kim
Cc: Michal Nazarewicz
Cc: Naoya Horiguchi
Cc: Christoph Lameter
Cc: Rik van Riel
Acked-by: David Rientjes
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
Unlike the migration scanner, the free scanner remembers the beginning of
the last scanned pageblock in cc->free_pfn. It might be therefore
rescanning pages uselessly when called several times during single
compaction. This might have been useful when pages were returned to the
buddy allocator after a failed migration, but this is no longer the case.This patch changes the meaning of cc->free_pfn so that if it points to a
middle of a pageblock, that pageblock is scanned only from cc->free_pfn to
the end. isolate_freepages_block() will record the pfn of the last page
it looked at, which is then used to update cc->free_pfn.In the mmtests stress-highalloc benchmark, this has resulted in lowering
the ratio between pages scanned by both scanners, from 2.5 free pages per
migrate page, to 2.25 free pages per migrate page, without affecting
success rates.With __GFP_NO_KSWAPD allocations, this appears to result in a worse ratio
(2.1 instead of 1.8), but page migration successes increased by 10%, so
this could mean that more useful work can be done until need_resched()
aborts this kind of compaction.Signed-off-by: Vlastimil Babka
Reviewed-by: Zhang Yanfei
Reviewed-by: Naoya Horiguchi
Acked-by: David Rientjes
Acked-by: Minchan Kim
Acked-by: Mel Gorman
Cc: Joonsoo Kim
Cc: Michal Nazarewicz
Cc: Naoya Horiguchi
Cc: Christoph Lameter
Cc: Rik van Riel
Cc: Zhang Yanfei
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
Compaction scanners try to lock zone locks as late as possible by checking
many page or pageblock properties opportunistically without lock and
skipping them if not unsuitable. For pages that pass the initial checks,
some properties have to be checked again safely under lock. However, if
the lock was already held from a previous iteration in the initial checks,
the rechecks are unnecessary.This patch therefore skips the rechecks when the lock was already held.
This is now possible to do, since we don't (potentially) drop and
reacquire the lock between the initial checks and the safe rechecks
anymore.Signed-off-by: Vlastimil Babka
Reviewed-by: Zhang Yanfei
Reviewed-by: Naoya Horiguchi
Acked-by: Minchan Kim
Acked-by: Mel Gorman
Cc: Michal Nazarewicz
Cc: Naoya Horiguchi
Cc: Christoph Lameter
Cc: Rik van Riel
Acked-by: David Rientjes
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
Compaction scanners regularly check for lock contention and need_resched()
through the compact_checklock_irqsave() function. However, if there is no
contention, the lock can be held and IRQ disabled for potentially long
time.This has been addressed by commit b2eef8c0d091 ("mm: compaction: minimise
the time IRQs are disabled while isolating pages for migration") for the
migration scanner. However, the refactoring done by commit 2a1402aa044b
("mm: compaction: acquire the zone->lru_lock as late as possible") has
changed the conditions so that the lock is dropped only when there's
contention on the lock or need_resched() is true. Also, need_resched() is
checked only when the lock is already held. The comment "give a chance to
irqs before checking need_resched" is therefore misleading, as IRQs remain
disabled when the check is done.This patch restores the behavior intended by commit b2eef8c0d091 and also
tries to better balance and make more deterministic the time spent by
checking for contention vs the time the scanners might run between the
checks. It also avoids situations where checking has not been done often
enough before. The result should be avoiding both too frequent and too
infrequent contention checking, and especially the potentially
long-running scans with IRQs disabled and no checking of need_resched() or
for fatal signal pending, which can happen when many consecutive pages or
pageblocks fail the preliminary tests and do not reach the later call site
to compact_checklock_irqsave(), as explained below.Before the patch:
In the migration scanner, compact_checklock_irqsave() was called each
loop, if reached. If not reached, some lower-frequency checking could
still be done if the lock was already held, but this would not result in
aborting contended async compaction until reaching
compact_checklock_irqsave() or end of pageblock. In the free scanner, it
was similar but completely without the periodical checking, so lock can be
potentially held until reaching the end of pageblock.After the patch, in both scanners:
The periodical check is done as the first thing in the loop on each
SWAP_CLUSTER_MAX aligned pfn, using the new compact_unlock_should_abort()
function, which always unlocks the lock (if locked) and aborts async
compaction if scheduling is needed. It also aborts any type of compaction
when a fatal signal is pending.The compact_checklock_irqsave() function is replaced with a slightly
different compact_trylock_irqsave(). The biggest difference is that the
function is not called at all if the lock is already held. The periodical
need_resched() checking is left solely to compact_unlock_should_abort().
The lock contention avoidance for async compaction is achieved by the
periodical unlock by compact_unlock_should_abort() and by using trylock in
compact_trylock_irqsave() and aborting when trylock fails. Sync
compaction does not use trylock.Signed-off-by: Vlastimil Babka
Reviewed-by: Zhang Yanfei
Acked-by: Minchan Kim
Acked-by: Mel Gorman
Cc: Michal Nazarewicz
Cc: Naoya Horiguchi
Cc: Christoph Lameter
Cc: Rik van Riel
Acked-by: David Rientjes
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
Async compaction aborts when it detects zone lock contention or
need_resched() is true. David Rientjes has reported that in practice,
most direct async compactions for THP allocation abort due to
need_resched(). This means that a second direct compaction is never
attempted, which might be OK for a page fault, but khugepaged is intended
to attempt a sync compaction in such case and in these cases it won't.This patch replaces "bool contended" in compact_control with an int that
distinguishes between aborting due to need_resched() and aborting due to
lock contention. This allows propagating the abort through all compaction
functions as before, but passing the abort reason up to
__alloc_pages_slowpath() which decides when to continue with direct
reclaim and another compaction attempt.Another problem is that try_to_compact_pages() did not act upon the
reported contention (both need_resched() or lock contention) immediately
and would proceed with another zone from the zonelist. When
need_resched() is true, that means initializing another zone compaction,
only to check again need_resched() in isolate_migratepages() and aborting.
For zone lock contention, the unintended consequence is that the lock
contended status reported back to the allocator is detrmined from the last
zone where compaction was attempted, which is rather arbitrary.This patch fixes the problem in the following way:
- async compaction of a zone aborting due to need_resched() or fatal signal
pending means that further zones should not be tried. We report
COMPACT_CONTENDED_SCHED to the allocator.
- aborting zone compaction due to lock contention means we can still try
another zone, since it has different set of locks. We report back
COMPACT_CONTENDED_LOCK only if *all* zones where compaction was attempted,
it was aborted due to lock contention.As a result of these fixes, khugepaged will proceed with second sync
compaction as intended, when the preceding async compaction aborted due to
need_resched(). Page fault compactions aborting due to need_resched()
will spare some cycles previously wasted by initializing another zone
compaction only to abort again. Lock contention will be reported only
when compaction in all zones aborted due to lock contention, and therefore
it's not a good idea to try again after reclaim.In stress-highalloc from mmtests configured to use __GFP_NO_KSWAPD, this
has improved number of THP collapse allocations by 10%, which shows
positive effect on khugepaged. The benchmark's success rates are
unchanged as it is not recognized as khugepaged. Numbers of compact_stall
and compact_fail events have however decreased by 20%, with
compact_success still a bit improved, which is good. With benchmark
configured not to use __GFP_NO_KSWAPD, there is 6% improvement in THP
collapse allocations, and only slight improvement in stalls and failures.[akpm@linux-foundation.org: fix warnings]
Reported-by: David Rientjes
Signed-off-by: Vlastimil Babka
Cc: Minchan Kim
Acked-by: Mel Gorman
Cc: Joonsoo Kim
Cc: Michal Nazarewicz
Cc: Naoya Horiguchi
Cc: Christoph Lameter
Cc: Rik van Riel
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
The unification of the migrate and free scanner families of function has
highlighted a difference in how the scanners ensure they only isolate
pages of the intended zone. This is important for taking zone lock or lru
lock of the correct zone. Due to nodes overlapping, it is however
possible to encounter a different zone within the range of the zone being
compacted.The free scanner, since its inception by commit 748446bb6b5a ("mm:
compaction: memory compaction core"), has been checking the zone of the
first valid page in a pageblock, and skipping the whole pageblock if the
zone does not match.This checking was completely missing from the migration scanner at first,
and later added by commit dc9086004b3d ("mm: compaction: check for
overlapping nodes during isolation for migration") in a reaction to a bug
report. But the zone comparison in migration scanner is done once per a
single scanned page, which is more defensive and thus more costly than a
check per pageblock.This patch unifies the checking done in both scanners to once per
pageblock, through a new pageblock_pfn_to_page() function, which also
includes pfn_valid() checks. It is more defensive than the current free
scanner checks, as it checks both the first and last page of the
pageblock, but less defensive by the migration scanner per-page checks.
It assumes that node overlapping may result (on some architecture) in a
boundary between two nodes falling into the middle of a pageblock, but
that there cannot be a node0 node1 node0 interleaving within a single
pageblock.The result is more code being shared and a bit less per-page CPU cost in
the migration scanner.Signed-off-by: Vlastimil Babka
Cc: Minchan Kim
Acked-by: Mel Gorman
Cc: Joonsoo Kim
Cc: Michal Nazarewicz
Cc: Naoya Horiguchi
Cc: Christoph Lameter
Cc: Rik van Riel
Acked-by: David Rientjes
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
isolate_migratepages_range() is the main function of the compaction
scanner, called either on a single pageblock by isolate_migratepages()
during regular compaction, or on an arbitrary range by CMA's
__alloc_contig_migrate_range(). It currently perfoms two pageblock-wide
compaction suitability checks, and because of the CMA callpath, it tracks
if it crossed a pageblock boundary in order to repeat those checks.However, closer inspection shows that those checks are always true for CMA:
- isolation_suitable() is true because CMA sets cc->ignore_skip_hint to true
- migrate_async_suitable() check is skipped because CMA uses sync compactionWe can therefore move the compaction-specific checks to
isolate_migratepages() and simplify isolate_migratepages_range().
Furthermore, we can mimic the freepage scanner family of functions, which
has isolate_freepages_block() function called both by compaction from
isolate_freepages() and by CMA from isolate_freepages_range(), where each
use-case adds own specific glue code. This allows further code
simplification.Thus, we rename isolate_migratepages_range() to
isolate_migratepages_block() and limit its functionality to a single
pageblock (or its subset). For CMA, a new different
isolate_migratepages_range() is created as a CMA-specific wrapper for the
_block() function. The checks specific to compaction are moved to
isolate_migratepages(). As part of the unification of these two families
of functions, we remove the redundant zone parameter where applicable,
since zone pointer is already passed in cc->zone.Furthermore, going back to compact_zone() and compact_finished() when
pageblock is found unsuitable (now by isolate_migratepages()) is wasteful
- the checks are meant to skip pageblocks quickly. The patch therefore
also introduces a simple loop into isolate_migratepages() so that it does
not return immediately on failed pageblock checks, but keeps going until
isolate_migratepages_range() gets called once. Similarily to
isolate_freepages(), the function periodically checks if it needs to
reschedule or abort async compaction.[iamjoonsoo.kim@lge.com: fix isolated page counting bug in compaction]
Signed-off-by: Vlastimil Babka
Cc: Minchan Kim
Acked-by: Mel Gorman
Cc: Joonsoo Kim
Cc: Michal Nazarewicz
Cc: Naoya Horiguchi
Cc: Christoph Lameter
Cc: Rik van Riel
Cc: David Rientjes
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
isolate_freepages_block() rechecks if the pageblock is suitable to be a
target for migration after it has taken the zone->lock. However, the
check has been optimized to occur only once per pageblock, and
compact_checklock_irqsave() might be dropping and reacquiring lock, which
means somebody else might have changed the pageblock's migratetype
meanwhile.Furthermore, nothing prevents the migratetype to change right after
isolate_freepages_block() has finished isolating. Given how imperfect
this is, it's simpler to just rely on the check done in
isolate_freepages() without lock, and not pretend that the recheck under
lock guarantees anything. It is just a heuristic after all.Signed-off-by: Vlastimil Babka
Reviewed-by: Zhang Yanfei
Acked-by: Minchan Kim
Acked-by: Mel Gorman
Cc: Joonsoo Kim
Cc: Michal Nazarewicz
Cc: Naoya Horiguchi
Cc: Christoph Lameter
Cc: Rik van Riel
Acked-by: David Rientjes
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
When direct sync compaction is often unsuccessful, it may become deferred
for some time to avoid further useless attempts, both sync and async.
Successful high-order allocations un-defer compaction, while further
unsuccessful compaction attempts prolong the compaction deferred period.Currently the checking and setting deferred status is performed only on
the preferred zone of the allocation that invoked direct compaction. But
compaction itself is attempted on all eligible zones in the zonelist, so
the behavior is suboptimal and may lead both to scenarios where 1)
compaction is attempted uselessly, or 2) where it's not attempted despite
good chances of succeeding, as shown on the examples below:1) A direct compaction with Normal preferred zone failed and set
deferred compaction for the Normal zone. Another unrelated direct
compaction with DMA32 as preferred zone will attempt to compact DMA32
zone even though the first compaction attempt also included DMA32 zone.In another scenario, compaction with Normal preferred zone failed to
compact Normal zone, but succeeded in the DMA32 zone, so it will not
defer compaction. In the next attempt, it will try Normal zone which
will fail again, instead of skipping Normal zone and trying DMA32
directly.2) Kswapd will balance DMA32 zone and reset defer status based on
watermarks looking good. A direct compaction with preferred Normal
zone will skip compaction of all zones including DMA32 because Normal
was still deferred. The allocation might have succeeded in DMA32, but
won't.This patch makes compaction deferring work on individual zone basis
instead of preferred zone. For each zone, it checks compaction_deferred()
to decide if the zone should be skipped. If watermarks fail after
compacting the zone, defer_compaction() is called. The zone where
watermarks passed can still be deferred when the allocation attempt is
unsuccessful. When allocation is successful, compaction_defer_reset() is
called for the zone containing the allocated page. This approach should
approximate calling defer_compaction() only on zones where compaction was
attempted and did not yield allocated page. There might be corner cases
but that is inevitable as long as the decision to stop compacting dues not
guarantee that a page will be allocated.Due to a new COMPACT_DEFERRED return value, some functions relying
implicitly on COMPACT_SKIPPED = 0 had to be updated, with comments made
more accurate. The did_some_progress output parameter of
__alloc_pages_direct_compact() is removed completely, as the caller
actually does not use it after compaction sets it - it is only considered
when direct reclaim sets it.During testing on a two-node machine with a single very small Normal zone
on node 1, this patch has improved success rates in stress-highalloc
mmtests benchmark. The success here were previously made worse by commit
3a025760fc15 ("mm: page_alloc: spill to remote nodes before waking
kswapd") as kswapd was no longer resetting often enough the deferred
compaction for the Normal zone, and DMA32 zones on both nodes were thus
not considered for compaction. On different machine, success rates were
improved with __GFP_NO_KSWAPD allocations.[akpm@linux-foundation.org: fix CONFIG_COMPACTION=n build]
Signed-off-by: Vlastimil Babka
Acked-by: Minchan Kim
Reviewed-by: Zhang Yanfei
Acked-by: Mel Gorman
Cc: Joonsoo Kim
Cc: Michal Nazarewicz
Cc: Naoya Horiguchi
Cc: Christoph Lameter
Cc: Rik van Riel
Cc: David Rientjes
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds
05 Jun, 2014
10 commits
-
Compaction uses compact_checklock_irqsave() function to periodically check
for lock contention and need_resched() to either abort async compaction,
or to free the lock, schedule and retake the lock. When aborting,
cc->contended is set to signal the contended state to the caller. Two
problems have been identified in this mechanism.First, compaction also calls directly cond_resched() in both scanners when
no lock is yet taken. This call either does not abort async compaction,
or set cc->contended appropriately. This patch introduces a new
compact_should_abort() function to achieve both. In isolate_freepages(),
the check frequency is reduced to once by SWAP_CLUSTER_MAX pageblocks to
match what the migration scanner does in the preliminary page checks. In
case a pageblock is found suitable for calling isolate_freepages_block(),
the checks within there are done on higher frequency.Second, isolate_freepages() does not check if isolate_freepages_block()
aborted due to contention, and advances to the next pageblock. This
violates the principle of aborting on contention, and might result in
pageblocks not being scanned completely, since the scanning cursor is
advanced. This problem has been noticed in the code by Joonsoo Kim when
reviewing related patches. This patch makes isolate_freepages_block()
check the cc->contended flag and abort.In case isolate_freepages() has already isolated some pages before
aborting due to contention, page migration will proceed, which is OK since
we do not want to waste the work that has been done, and page migration
has own checks for contention. However, we do not want another isolation
attempt by either of the scanners, so cc->contended flag check is added
also to compaction_alloc() and compact_finished() to make sure compaction
is aborted right after the migration.The outcome of the patch should be reduced lock contention by async
compaction and lower latencies for higher-order allocations where direct
compaction is involved.[akpm@linux-foundation.org: fix typo in comment]
Reported-by: Joonsoo Kim
Signed-off-by: Vlastimil Babka
Reviewed-by: Naoya Horiguchi
Cc: Minchan Kim
Cc: Mel Gorman
Cc: Bartlomiej Zolnierkiewicz
Cc: Michal Nazarewicz
Cc: Christoph Lameter
Cc: Rik van Riel
Acked-by: Michal Nazarewicz
Tested-by: Shawn Guo
Tested-by: Kevin Hilman
Tested-by: Stephen Warren
Tested-by: Fabio Estevam
Cc: David Rientjes
Cc: Stephen Rothwell
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
The compaction free scanner in isolate_freepages() currently remembers PFN
of the highest pageblock where it successfully isolates, to be used as the
starting pageblock for the next invocation. The rationale behind this is
that page migration might return free pages to the allocator when
migration fails and we don't want to skip them if the compaction
continues.Since migration now returns free pages back to compaction code where they
can be reused, this is no longer a concern. This patch changes
isolate_freepages() so that the PFN for restarting is updated with each
pageblock where isolation is attempted. Using stress-highalloc from
mmtests, this resulted in 10% reduction of the pages scanned by the free
scanner.Note that the somewhat similar functionality that records highest
successful pageblock in zone->compact_cached_free_pfn, remains unchanged.
This cache is used when the whole compaction is restarted, not for
multiple invocations of the free scanner during single compaction.Signed-off-by: Vlastimil Babka
Cc: Minchan Kim
Cc: Mel Gorman
Cc: Joonsoo Kim
Cc: Bartlomiej Zolnierkiewicz
Acked-by: Michal Nazarewicz
Reviewed-by: Naoya Horiguchi
Cc: Christoph Lameter
Cc: Rik van Riel
Acked-by: David Rientjes
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
During compaction, update_nr_listpages() has been used to count remaining
non-migrated and free pages after a call to migrage_pages(). The
freepages counting has become unneccessary, and it turns out that
migratepages counting is also unnecessary in most cases.The only situation when it's needed to count cc->migratepages is when
migrate_pages() returns with a negative error code. Otherwise, the
non-negative return value is the number of pages that were not migrated,
which is exactly the count of remaining pages in the cc->migratepages
list.Furthermore, any non-zero count is only interesting for the tracepoint of
mm_compaction_migratepages events, because after that all remaining
unmigrated pages are put back and their count is set to 0.This patch therefore removes update_nr_listpages() completely, and changes
the tracepoint definition so that the manual counting is done only when
the tracepoint is enabled, and only when migrate_pages() returns a
negative error code.Furthermore, migrate_pages() and the tracepoints won't be called when
there's nothing to migrate. This potentially avoids some wasted cycles
and reduces the volume of uninteresting mm_compaction_migratepages events
where "nr_migrated=0 nr_failed=0". In the stress-highalloc mmtest, this
was about 75% of the events. The mm_compaction_isolate_migratepages event
is better for determining that nothing was isolated for migration, and
this one was just duplicating the info.Signed-off-by: Vlastimil Babka
Reviewed-by: Naoya Horiguchi
Cc: Minchan Kim
Cc: Mel Gorman
Cc: Joonsoo Kim
Cc: Bartlomiej Zolnierkiewicz
Acked-by: Michal Nazarewicz
Cc: Christoph Lameter
Cc: Rik van Riel
Acked-by: David Rientjes
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
Async compaction terminates prematurely when need_resched(), see
compact_checklock_irqsave(). This can never trigger, however, if the
cond_resched() in isolate_migratepages_range() always takes care of the
scheduling.If the cond_resched() actually triggers, then terminate this pageblock
scan for async compaction as well.Signed-off-by: David Rientjes
Acked-by: Mel Gorman
Acked-by: Vlastimil Babka
Cc: Mel Gorman
Cc: Vlastimil Babka
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
We're going to want to manipulate the migration mode for compaction in the
page allocator, and currently compact_control's sync field is only a bool.Currently, we only do MIGRATE_ASYNC or MIGRATE_SYNC_LIGHT compaction
depending on the value of this bool. Convert the bool to enum
migrate_mode and pass the migration mode in directly. Later, we'll want
to avoid MIGRATE_SYNC_LIGHT for thp allocations in the pagefault patch to
avoid unnecessary latency.This also alters compaction triggered from sysfs, either for the entire
system or for a node, to force MIGRATE_SYNC.[akpm@linux-foundation.org: fix build]
[iamjoonsoo.kim@lge.com: use MIGRATE_SYNC in alloc_contig_range()]
Signed-off-by: David Rientjes
Suggested-by: Mel Gorman
Acked-by: Vlastimil Babka
Cc: Greg Thelen
Cc: Naoya Horiguchi
Signed-off-by: Joonsoo Kim
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
Each zone has a cached migration scanner pfn for memory compaction so that
subsequent calls to memory compaction can start where the previous call
left off.Currently, the compaction migration scanner only updates the per-zone
cached pfn when pageblocks were not skipped for async compaction. This
creates a dependency on calling sync compaction to avoid having subsequent
calls to async compaction from scanning an enormous amount of non-MOVABLE
pageblocks each time it is called. On large machines, this could be
potentially very expensive.This patch adds a per-zone cached migration scanner pfn only for async
compaction. It is updated everytime a pageblock has been scanned in its
entirety and when no pages from it were successfully isolated. The cached
migration scanner pfn for sync compaction is updated only when called for
sync compaction.Signed-off-by: David Rientjes
Acked-by: Vlastimil Babka
Reviewed-by: Naoya Horiguchi
Cc: Greg Thelen
Cc: Mel Gorman
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
Greg reported that he found isolated free pages were returned back to the
VM rather than the compaction freelist. This will cause holes behind the
free scanner and cause it to reallocate additional memory if necessary
later.He detected the problem at runtime seeing that ext4 metadata pages (esp
the ones read by "sbi->s_group_desc[i] = sb_bread(sb, block)") were
constantly visited by compaction calls of migrate_pages(). These pages
had a non-zero b_count which caused fallback_migrate_page() ->
try_to_release_page() -> try_to_free_buffers() to fail.Memory compaction works by having a "freeing scanner" scan from one end of
a zone which isolates pages as migration targets while another "migrating
scanner" scans from the other end of the same zone which isolates pages
for migration.When page migration fails for an isolated page, the target page is
returned to the system rather than the freelist built by the freeing
scanner. This may require the freeing scanner to continue scanning memory
after suitable migration targets have already been returned to the system
needlessly.This patch returns destination pages to the freeing scanner freelist when
page migration fails. This prevents unnecessary work done by the freeing
scanner but also encourages memory to be as compacted as possible at the
end of the zone.Signed-off-by: David Rientjes
Reported-by: Greg Thelen
Acked-by: Mel Gorman
Acked-by: Vlastimil Babka
Reviewed-by: Naoya Horiguchi
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
Memory migration uses a callback defined by the caller to determine how to
allocate destination pages. When migration fails for a source page,
however, it frees the destination page back to the system.This patch adds a memory migration callback defined by the caller to
determine how to free destination pages. If a caller, such as memory
compaction, builds its own freelist for migration targets, this can reuse
already freed memory instead of scanning additional memory.If the caller provides a function to handle freeing of destination pages,
it is called when page migration fails. If the caller passes NULL then
freeing back to the system will be handled as usual. This patch
introduces no functional change.Signed-off-by: David Rientjes
Reviewed-by: Naoya Horiguchi
Acked-by: Mel Gorman
Acked-by: Vlastimil Babka
Cc: Greg Thelen
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
isolate_freepages() is currently somewhat hard to follow thanks to many
looks like it is related to the 'low_pfn' variable, but in fact it is not.This patch renames the 'high_pfn' variable to a hopefully less confusing name,
and slightly changes its handling without a functional change. A comment made
obsolete by recent changes is also updated.[akpm@linux-foundation.org: comment fixes, per Minchan]
[iamjoonsoo.kim@lge.com: cleanups]
Signed-off-by: Vlastimil Babka
Cc: Minchan Kim
Cc: Mel Gorman
Cc: Joonsoo Kim
Cc: Bartlomiej Zolnierkiewicz
Cc: Michal Nazarewicz
Cc: Naoya Horiguchi
Cc: Christoph Lameter
Cc: Rik van Riel
Cc: Dongjun Shin
Cc: Sunghwan Yun
Signed-off-by: Joonsoo Kim
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
Remove code lines currently not in use or never called.
Signed-off-by: Heesub Shin
Acked-by: Vlastimil Babka
Cc: Dongjun Shin
Cc: Sunghwan Yun
Cc: Minchan Kim
Cc: Mel Gorman
Cc: Joonsoo Kim
Cc: Bartlomiej Zolnierkiewicz
Cc: Michal Nazarewicz
Cc: Naoya Horiguchi
Cc: Christoph Lameter
Cc: Rik van Riel
Cc: Dongjun Shin
Cc: Sunghwan Yun
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds
07 May, 2014
1 commit
-
The compaction freepage scanner implementation in isolate_freepages()
starts by taking the current cc->free_pfn value as the first pfn. In a
for loop, it scans from this first pfn to the end of the pageblock, and
then subtracts pageblock_nr_pages from the first pfn to obtain the first
pfn for the next for loop iteration.This means that when cc->free_pfn starts at offset X rather than being
aligned on pageblock boundary, the scanner will start at offset X in all
scanned pageblock, ignoring potentially many free pages. Currently this
can happen whena) zone's end pfn is not pageblock aligned, or
b) through zone->compact_cached_free_pfn with CONFIG_HOLES_IN_ZONE
enabled and a hole spanning the beginning of a pageblockThis patch fixes the problem by aligning the initial pfn in
isolate_freepages() to pageblock boundary. This also permits replacing
the end-of-pageblock alignment within the for loop with a simple
pageblock_nr_pages increment.Signed-off-by: Vlastimil Babka
Reported-by: Heesub Shin
Acked-by: Minchan Kim
Cc: Mel Gorman
Acked-by: Joonsoo Kim
Cc: Bartlomiej Zolnierkiewicz
Cc: Michal Nazarewicz
Cc: Naoya Horiguchi
Cc: Christoph Lameter
Acked-by: Rik van Riel
Cc: Dongjun Shin
Cc: Sunghwan Yun
Cc:
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds
08 Apr, 2014
6 commits
-
The conditions that control the isolation mode in
isolate_migratepages_range() do not change during the iteration, so
extract them out and only define the value once.This actually does have an effect, gcc doesn't optimize it itself because
of cc->sync.Signed-off-by: David Rientjes
Cc: Mel Gorman
Acked-by: Rik van Riel
Acked-by: Vlastimil Babka
Cc: Joonsoo Kim
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
It is just for clean-up to reduce code size and improve readability.
There is no functional change.Signed-off-by: Joonsoo Kim
Acked-by: Vlastimil Babka
Cc: Mel Gorman
Cc: Rik van Riel
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
isolation_suitable() and migrate_async_suitable() is used to be sure
that this pageblock range is fine to be migragted. It isn't needed to
call it on every page. Current code do well if not suitable, but, don't
do well when suitable.1) It re-checks isolation_suitable() on each page of a pageblock that was
already estabilished as suitable.
2) It re-checks migrate_async_suitable() on each page of a pageblock that
was not entered through the next_pageblock: label, because
last_pageblock_nr is not otherwise updated.This patch fixes situation by 1) calling isolation_suitable() only once
per pageblock and 2) always updating last_pageblock_nr to the pageblock
that was just checked.Additionally, move PageBuddy() check after pageblock unit check, since
pageblock check is the first thing we should do and makes things more
simple.[vbabka@suse.cz: rephrase commit description]
Signed-off-by: Joonsoo Kim
Acked-by: Vlastimil Babka
Cc: Mel Gorman
Cc: Rik van Riel
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
It is odd to drop the spinlock when we scan (SWAP_CLUSTER_MAX - 1) th
pfn page. This may results in below situation while isolating
migratepage.1. try isolate 0x0 ~ 0x200 pfn pages.
2. When low_pfn is 0x1ff, ((low_pfn+1) % SWAP_CLUSTER_MAX) == 0, so drop
the spinlock.
3. Then, to complete isolating, retry to aquire the lock.I think that it is better to use SWAP_CLUSTER_MAX th pfn for checking the
criteria about dropping the lock. This has no harm 0x0 pfn, because, at
this time, locked variable would be false.Signed-off-by: Joonsoo Kim
Acked-by: Vlastimil Babka
Cc: Mel Gorman
Cc: Rik van Riel
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
suitable_migration_target() checks that pageblock is suitable for
migration target. In isolate_freepages_block(), it is called on every
page and this is inefficient. So make it called once per pageblock.suitable_migration_target() also checks if page is highorder or not, but
it's criteria for highorder is pageblock order. So calling it once
within pageblock range has no problem.Signed-off-by: Joonsoo Kim
Acked-by: Vlastimil Babka
Cc: Mel Gorman
Cc: Rik van Riel
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
Purpose of compaction is to get a high order page. Currently, if we
find high-order page while searching migration target page, we break it
to order-0 pages and use them as migration target. It is contrary to
purpose of compaction, so disallow high-order page to be used for
migration target.Additionally, clean-up logic in suitable_migration_target() to simplify
the code. There is no functional changes from this clean-up.Signed-off-by: Joonsoo Kim
Acked-by: Vlastimil Babka
Cc: Mel Gorman
Cc: Rik van Riel
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds
04 Apr, 2014
3 commits
-
Mark function as static in compaction.c because it is not used outside
this file.This eliminates the following warning from mm/compaction.c:
mm/compaction.c:1190:9: warning: no previous prototype for `sysfs_compact_node' [-Wmissing-prototypes
Signed-off-by: Rashika Kheria
Reviewed-by: Josh Triplett
Reviewed-by: Rik van Riel
Acked-by: David Rientjes
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
Page migration will fail for memory that is pinned in memory with, for
example, get_user_pages(). In this case, it is unnecessary to take
zone->lru_lock or isolating the page and passing it to page migration
which will ultimately fail.This is a racy check, the page can still change from under us, but in
that case we'll just fail later when attempting to move the page.This avoids very expensive memory compaction when faulting transparent
hugepages after pinning a lot of memory with a Mellanox driver.On a 128GB machine and pinning ~120GB of memory, before this patch we
see the enormous disparity in the number of page migration failures
because of the pinning (from /proc/vmstat):compact_pages_moved 8450
compact_pagemigrate_failed 156144150.05% of pages isolated are successfully migrated and explicitly
triggering memory compaction takes 102 seconds. After the patch:compact_pages_moved 9197
compact_pagemigrate_failed 799.9% of pages isolated are now successfully migrated in this
configuration and memory compaction takes less than one second.Signed-off-by: David Rientjes
Acked-by: Hugh Dickins
Acked-by: Mel Gorman
Cc: Joonsoo Kim
Cc: Rik van Riel
Cc: Greg Thelen
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
The cached pageblock hint should be ignored when triggering compaction
through /proc/sys/vm/compact_memory so all eligible memory is isolated.
Manually invoking compaction is known to be expensive, there's no need
to skip pageblocks based on heuristics (mainly for debugging).Signed-off-by: David Rientjes
Acked-by: Mel Gorman
Cc: Rik van Riel
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds
11 Mar, 2014
1 commit
-
We received several reports of bad page state when freeing CMA pages
previously allocated with alloc_contig_range:BUG: Bad page state in process Binder_A pfn:63202
page:d21130b0 count:0 mapcount:1 mapping: (null) index:0x7dfbf
page flags: 0x40080068(uptodate|lru|active|swapbacked)Based on the page state, it looks like the page was still in use. The
page flags do not make sense for the use case though. Further debugging
showed that despite alloc_contig_range returning success, at least one
page in the range still remained in the buddy allocator.There is an issue with isolate_freepages_block. In strict mode (which
CMA uses), if any pages in the range cannot be isolated,
isolate_freepages_block should return failure 0. The current check
keeps track of the total number of isolated pages and compares against
the size of the range:if (strict && nr_strict_required > total_isolated)
total_isolated = 0;After taking the zone lock, if one of the pages in the range is not in
the buddy allocator, we continue through the loop and do not increment
total_isolated. If in the last iteration of the loop we isolate more
than one page (e.g. last page needed is a higher order page), the check
for total_isolated may pass and we fail to detect that a page was
skipped. The fix is to bail out if the loop immediately if we are in
strict mode. There's no benfit to continuing anyway since we need all
pages to be isolated. Additionally, drop the error checking based on
nr_strict_required and just check the pfn ranges. This matches with
what isolate_freepages_range does.Signed-off-by: Laura Abbott
Acked-by: Minchan Kim
Cc: Mel Gorman
Acked-by: Vlastimil Babka
Cc: Joonsoo Kim
Acked-by: Bartlomiej Zolnierkiewicz
Acked-by: Michal Nazarewicz
Cc:
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds
24 Jan, 2014
2 commits
-
Developers occasionally try and optimise PFN scanners by using
page_order but miss that in general it requires zone->lock. This has
happened twice for compaction.c and rejected both times. This patch
clarifies the documentation of page_order and adds a note to
compaction.c why page_order is not used.[akpm@linux-foundation.org: tweaks]
[lauraa@codeaurora.org: Corrected a page_zone(page)->lock reference]
Signed-off-by: Mel Gorman
Acked-by: Rafael Aquini
Acked-by: Minchan Kim
Cc: Laura Abbott
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
Most of the VM_BUG_ON assertions are performed on a page. Usually, when
one of these assertions fails we'll get a BUG_ON with a call stack and
the registers.I've recently noticed based on the requests to add a small piece of code
that dumps the page to various VM_BUG_ON sites that the page dump is
quite useful to people debugging issues in mm.This patch adds a VM_BUG_ON_PAGE(cond, page) which beyond doing what
VM_BUG_ON() does, also dumps the page before executing the actual
BUG_ON.[akpm@linux-foundation.org: fix up includes]
Signed-off-by: Sasha Levin
Cc: "Kirill A. Shutemov"
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds
22 Jan, 2014
1 commit
-
Compaction used to start its migrate and free page scaners at the zone's
lowest and highest pfn, respectively. Later, caching was introduced to
remember the scanners' progress across compaction attempts so that
pageblocks are not re-scanned uselessly. Additionally, pageblocks where
isolation failed are marked to be quickly skipped when encountered again
in future compactions.Currently, both the reset of cached pfn's and clearing of the pageblock
skip information for a zone is done in __reset_isolation_suitable().
This function gets called when:- compaction is restarting after being deferred
- compact_blockskip_flush flag is set in compact_finished() when the scanners
meet (and not again cleared when direct compaction succeeds in allocation)
and kswapd acts upon this flag before going to sleepThis behavior is suboptimal for several reasons:
- when direct sync compaction is called after async compaction fails (in the
allocation slowpath), it will effectively do nothing, unless kswapd
happens to process the compact_blockskip_flush flag meanwhile. This is racy
and goes against the purpose of sync compaction to more thoroughly retry
the compaction of a zone where async compaction has failed.
The restart-after-deferring path cannot help here as deferring happens only
after the sync compaction fails. It is also done only for the preferred
zone, while the compaction might be done for a fallback zone.- the mechanism of marking pageblock to be skipped has little value since the
cached pfn's are reset only together with the pageblock skip flags. This
effectively limits pageblock skip usage to parallel compactions.This patch changes compact_finished() so that cached pfn's are reset
immediately when the scanners meet. Clearing pageblock skip flags is
unchanged, as well as the other situations where cached pfn's are reset.
This allows the sync-after-async compaction to retry pageblocks not
marked as skipped, such as blocks !MIGRATE_MOVABLE blocks that async
compactions now skips without marking them.Signed-off-by: Vlastimil Babka
Cc: Rik van Riel
Acked-by: Mel Gorman
Cc: Joonsoo Kim
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds