16 Jan, 2016
40 commits
-
Both page_referenced() and page_idle_clear_pte_refs_one() assume that
THP can only be mapped with PMD, so there's no reason to look on PTEs
for PageTransHuge() pages. That's no true anymore: THP can be mapped
with PTEs too.The patch removes PageTransHuge() test from the functions and opencode
page table check.[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Kirill A. Shutemov
Cc: Vladimir Davydov
Cc: Andrea Arcangeli
Cc: Hugh Dickins
Cc: Naoya Horiguchi
Cc: Sasha Levin
Cc: Minchan Kim
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
Before THP refcounting rework, THP was not allowed to cross VMA
boundary. So, if we have THP and we split it, PG_mlocked can be safely
transferred to small pages.With new THP refcounting and naive approach to mlocking we can end up
with this scenario:
1. we have a mlocked THP, which belong to one VM_LOCKED VMA.
2. the process does munlock() on the *part* of the THP:
- the VMA is split into two, one of them VM_LOCKED;
- huge PMD split into PTE table;
- THP is still mlocked;
3. split_huge_page():
- it transfers PG_mlocked to *all* small pages regrardless if it
blong to any VM_LOCKED VMA.We probably could munlock() all small pages on split_huge_page(), but I
think we have accounting issue already on step two.Instead of forbidding mlocked pages altogether, we just avoid mlocking
PTE-mapped THPs and munlock THPs on split_huge_pmd().This means PTE-mapped THPs will be on normal lru lists and will be split
under memory pressure by vmscan. After the split vmscan will detect
unevictable small pages and mlock them.With this approach we shouldn't hit situation like described above.
Signed-off-by: Kirill A. Shutemov
Cc: Sasha Levin
Cc: Aneesh Kumar K.V
Cc: Jerome Marchand
Cc: Vlastimil Babka
Cc: Andrea Arcangeli
Cc: Hugh Dickins
Cc: Dave Hansen
Cc: Mel Gorman
Cc: Rik van Riel
Cc: Naoya Horiguchi
Cc: Steve Capper
Cc: Johannes Weiner
Cc: Michal Hocko
Cc: Christoph Lameter
Cc: David Rientjes
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
The patch updates Documentation/vm/transhuge.txt to reflect changes in
THP design.Signed-off-by: Kirill A. Shutemov
Acked-by: Jerome Marchand
Cc: Sasha Levin
Cc: Aneesh Kumar K.V
Cc: Andrea Arcangeli
Cc: Hugh Dickins
Cc: Dave Hansen
Cc: Mel Gorman
Cc: Rik van Riel
Cc: Naoya Horiguchi
Cc: Steve Capper
Cc: Johannes Weiner
Cc: Michal Hocko
Cc: Christoph Lameter
Cc: David Rientjes
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
All parts of THP with new refcounting are now in place. We can now
allow to enable THP.Signed-off-by: Kirill A. Shutemov
Tested-by: Sasha Levin
Tested-by: Aneesh Kumar K.V
Acked-by: Jerome Marchand
Cc: Vlastimil Babka
Cc: Andrea Arcangeli
Cc: Hugh Dickins
Cc: Dave Hansen
Cc: Mel Gorman
Cc: Rik van Riel
Cc: Naoya Horiguchi
Cc: Steve Capper
Cc: Johannes Weiner
Cc: Michal Hocko
Cc: Christoph Lameter
Cc: David Rientjes
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
Currently we don't split huge page on partial unmap. It's not an ideal
situation. It can lead to memory overhead.Furtunately, we can detect partial unmap on page_remove_rmap(). But we
cannot call split_huge_page() from there due to locking context.It's also counterproductive to do directly from munmap() codepath: in
many cases we will hit this from exit(2) and splitting the huge page
just to free it up in small pages is not what we really want.The patch introduce deferred_split_huge_page() which put the huge page
into queue for splitting. The splitting itself will happen when we get
memory pressure via shrinker interface. The page will be dropped from
list on freeing through compound page destructor.Signed-off-by: Kirill A. Shutemov
Tested-by: Sasha Levin
Tested-by: Aneesh Kumar K.V
Acked-by: Vlastimil Babka
Acked-by: Jerome Marchand
Cc: Andrea Arcangeli
Cc: Hugh Dickins
Cc: Dave Hansen
Cc: Mel Gorman
Cc: Rik van Riel
Cc: Naoya Horiguchi
Cc: Steve Capper
Cc: Johannes Weiner
Cc: Michal Hocko
Cc: Christoph Lameter
Cc: David Rientjes
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
We are not able to migrate THPs. It means it's not enough to split only
PMD on migration -- we need to split compound page under it too.Signed-off-by: Kirill A. Shutemov
Tested-by: Aneesh Kumar K.V
Acked-by: Jerome Marchand
Cc: Sasha Levin
Cc: Vlastimil Babka
Cc: Andrea Arcangeli
Cc: Hugh Dickins
Cc: Dave Hansen
Cc: Mel Gorman
Cc: Rik van Riel
Cc: Naoya Horiguchi
Cc: Steve Capper
Cc: Johannes Weiner
Cc: Michal Hocko
Cc: Christoph Lameter
Cc: David Rientjes
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
This patch adds implementation of split_huge_page() for new
refcountings.Unlike previous implementation, new split_huge_page() can fail if
somebody holds GUP pin on the page. It also means that pin on page
would prevent it from bening split under you. It makes situation in
many places much cleaner.The basic scheme of split_huge_page():
- Check that sum of mapcounts of all subpage is equal to page_count()
plus one (caller pin). Foll off with -EBUSY. This way we can avoid
useless PMD-splits.- Freeze the page counters by splitting all PMD and setup migration
PTEs.- Re-check sum of mapcounts against page_count(). Page's counts are
stable now. -EBUSY if page is pinned.- Split compound page.
- Unfreeze the page by removing migration entries.
Signed-off-by: Kirill A. Shutemov
Tested-by: Sasha Levin
Tested-by: Aneesh Kumar K.V
Acked-by: Jerome Marchand
Cc: Vlastimil Babka
Cc: Andrea Arcangeli
Cc: Hugh Dickins
Cc: Dave Hansen
Cc: Mel Gorman
Cc: Rik van Riel
Cc: Naoya Horiguchi
Cc: Steve Capper
Cc: Johannes Weiner
Cc: Michal Hocko
Cc: Christoph Lameter
Cc: David RientjesSigned-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
Some mm-related BUG_ON()s could trigger from hwpoison code due to recent
changes in thp refcounting rule. This patch fixes them up.In the new refcounting, we no longer use tail->_mapcount to keep tail's
refcount, and thereby we can simplify get/put_hwpoison_page().And another change is that tail's refcount is not transferred to the raw
page during thp split (more precisely, in new rule we don't take
refcount on tail page any more.) So when we need thp split, we have to
transfer the refcount properly to the 4kB soft-offlined page before
migration.thp split code goes into core code only when precheck
(total_mapcount(head) == page_count(head) - 1) passes to avoid useless
split, where we assume that one refcount is held by the caller of thp
split and the others are taken via mapping. To meet this assumption,
this patch moves thp split part in soft_offline_page() after
get_any_page().[akpm@linux-foundation.org: remove unneeded #define, per Kirill]
Signed-off-by: Naoya Horiguchi
Acked-by: Kirill A. Shutemov
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
I saw the following BUG_ON triggered in a testcase where a process calls
madvise(MADV_SOFT_OFFLINE) on thps, along with a background process that
calls migratepages command repeatedly (doing ping-pong among different
NUMA nodes) for the first process:Soft offlining page 0x60000 at 0x700000600000
__get_any_page: 0x60000 free buddy page
page:ffffea0001800000 count:0 mapcount:-127 mapping: (null) index:0x1
flags: 0x1fffc0000000000()
page dumped because: VM_BUG_ON_PAGE(atomic_read(&page->_count) == 0)
------------[ cut here ]------------
kernel BUG at /src/linux-dev/include/linux/mm.h:342!
invalid opcode: 0000 [#1] SMP DEBUG_PAGEALLOC
Modules linked in: cfg80211 rfkill crc32c_intel serio_raw virtio_balloon i2c_piix4 virtio_blk virtio_net ata_generic pata_acpi
CPU: 3 PID: 3035 Comm: test_alloc_gene Tainted: G O 4.4.0-rc8-v4.4-rc8-160107-1501-00000-rc8+ #74
Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
task: ffff88007c63d5c0 ti: ffff88007c210000 task.ti: ffff88007c210000
RIP: 0010:[] [] put_page+0x5c/0x60
RSP: 0018:ffff88007c213e00 EFLAGS: 00010246
Call Trace:
put_hwpoison_page+0x4e/0x80
soft_offline_page+0x501/0x520
SyS_madvise+0x6bc/0x6f0
entry_SYSCALL_64_fastpath+0x12/0x6a
Code: 8b fc ff ff 5b 5d c3 48 89 df e8 b0 fa ff ff 48 89 df 31 f6 e8 c6 7d ff ff 5b 5d c3 48 c7 c6 08 54 a2 81 48 89 df e8 a4 c5 01 00 0b 66 90 66 66 66 66 90 55 48 89 e5 41 55 41 54 53 48 8b 47
RIP [] put_page+0x5c/0x60
RSPThe root cause resides in get_any_page() which retries to get a refcount
of the page to be soft-offlined. This function calls
put_hwpoison_page(), expecting that the target page is putback to LRU
list. But it can be also freed to buddy. So the second check need to
care about such case.Fixes: af8fae7c0886 ("mm/memory-failure.c: clean up soft_offline_page()")
Signed-off-by: Naoya Horiguchi
Cc: Sasha Levin
Cc: Aneesh Kumar K.V
Cc: Vlastimil Babka
Cc: Jerome Marchand
Cc: Andrea Arcangeli
Cc: Hugh Dickins
Cc: Dave Hansen
Cc: Mel Gorman
Cc: Rik van Riel
Cc: Steve Capper
Cc: Johannes Weiner
Cc: Michal Hocko
Cc: Christoph Lameter
Cc: David Rientjes
Cc: [3.9+]
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
We're going to use migration entries instead of compound_lock() to
stabilize page refcounts. Setup and remove migration entries require
page to be locked.Some of split_huge_page() callers already have the page locked. Let's
require everybody to lock the page before calling split_huge_page().Signed-off-by: Kirill A. Shutemov
Tested-by: Sasha Levin
Tested-by: Aneesh Kumar K.V
Acked-by: Vlastimil Babka
Acked-by: Jerome Marchand
Cc: Andrea Arcangeli
Cc: Hugh Dickins
Cc: Dave Hansen
Cc: Mel Gorman
Cc: Rik van Riel
Cc: Naoya Horiguchi
Cc: Steve Capper
Cc: Johannes Weiner
Cc: Michal Hocko
Cc: Christoph Lameter
Cc: David Rientjes
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
We are going to use migration PTE entries to stabilize page counts. If
the page is mapped with PMDs we need to split the PMD and setup
migration entries. It's reasonable to combine these operations to avoid
double-scanning over the page table.Signed-off-by: Kirill A. Shutemov
Tested-by: Sasha Levin
Tested-by: Aneesh Kumar K.V
Acked-by: Vlastimil Babka
Acked-by: Jerome Marchand
Cc: Andrea Arcangeli
Cc: Hugh Dickins
Cc: Dave Hansen
Cc: Mel Gorman
Cc: Rik van Riel
Cc: Naoya Horiguchi
Cc: Steve Capper
Cc: Johannes Weiner
Cc: Michal Hocko
Cc: Christoph Lameter
Cc: David Rientjes
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
Original split_huge_page() combined two operations: splitting PMDs into
tables of PTEs and splitting underlying compound page. This patch
implements split_huge_pmd() which split given PMD without splitting
other PMDs this page mapped with or underlying compound page.Without tail page refcounting, implementation of split_huge_pmd() is
pretty straight-forward.Signed-off-by: Kirill A. Shutemov
Tested-by: Sasha Levin
Tested-by: Aneesh Kumar K.V
Acked-by: Jerome Marchand
Cc: Vlastimil Babka
Cc: Andrea Arcangeli
Cc: Hugh Dickins
Cc: Dave Hansen
Cc: Mel Gorman
Cc: Rik van Riel
Cc: Naoya Horiguchi
Cc: Steve Capper
Cc: Johannes Weiner
Cc: Michal Hocko
Cc: Christoph Lameter
Cc: David Rientjes
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
We're going to have THP mapped with PTEs. It will confuse
numabalancing. Let's skip them for now.Signed-off-by: Kirill A. Shutemov
Tested-by: Sasha Levin
Tested-by: Aneesh Kumar K.V
Acked-by: Jerome Marchand
Cc: Vlastimil Babka
Cc: Andrea Arcangeli
Cc: Hugh Dickins
Cc: Dave Hansen
Cc: Mel Gorman
Cc: Rik van Riel
Cc: Naoya Horiguchi
Cc: Steve Capper
Cc: Johannes Weiner
Cc: Michal Hocko
Cc: Christoph Lameter
Cc: David Rientjes
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
Let's define page_mapped() to be true for compound pages if any
sub-pages of the compound page is mapped (with PMD or PTE).On other hand page_mapcount() return mapcount for this particular small
page.This will make cases like page_get_anon_vma() behave correctly once we
allow huge pages to be mapped with PTE.Most users outside core-mm should use page_mapcount() instead of
page_mapped().Signed-off-by: Kirill A. Shutemov
Tested-by: Sasha Levin
Tested-by: Aneesh Kumar K.V
Acked-by: Jerome Marchand
Cc: Vlastimil Babka
Cc: Andrea Arcangeli
Cc: Hugh Dickins
Cc: Dave Hansen
Cc: Mel Gorman
Cc: Rik van Riel
Cc: Naoya Horiguchi
Cc: Steve Capper
Cc: Johannes Weiner
Cc: Michal Hocko
Cc: Christoph Lameter
Cc: David Rientjes
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
We're going to allow mapping of individual 4k pages of THP compound. It
means we need to track mapcount on per small page basis.Straight-forward approach is to use ->_mapcount in all subpages to track
how many time this subpage is mapped with PMDs or PTEs combined. But
this is rather expensive: mapping or unmapping of a THP page with PMD
would require HPAGE_PMD_NR atomic operations instead of single we have
now.The idea is to store separately how many times the page was mapped as
whole -- compound_mapcount. This frees up ->_mapcount in subpages to
track PTE mapcount.We use the same approach as with compound page destructor and compound
order to store compound_mapcount: use space in first tail page,
->mapping this time.Any time we map/unmap whole compound page (THP or hugetlb) -- we
increment/decrement compound_mapcount. When we map part of compound
page with PTE we operate on ->_mapcount of the subpage.page_mapcount() counts both: PTE and PMD mappings of the page.
Basically, we have mapcount for a subpage spread over two counters. It
makes tricky to detect when last mapcount for a page goes away.We introduced PageDoubleMap() for this. When we split THP PMD for the
first time and there's other PMD mapping left we offset up ->_mapcount
in all subpages by one and set PG_double_map on the compound page.
These additional references go away with last compound_mapcount.This approach provides a way to detect when last mapcount goes away on
per small page basis without introducing new overhead for most common
cases.[akpm@linux-foundation.org: fix typo in comment]
[mhocko@suse.com: ignore partial THP when moving task]
Signed-off-by: Kirill A. Shutemov
Tested-by: Aneesh Kumar K.V
Acked-by: Jerome Marchand
Cc: Sasha Levin
Cc: Aneesh Kumar K.V
Cc: Jerome Marchand
Cc: Vlastimil Babka
Cc: Andrea Arcangeli
Cc: Hugh Dickins
Cc: Dave Hansen
Cc: Mel Gorman
Cc: Rik van Riel
Cc: Naoya Horiguchi
Cc: Steve Capper
Cc: Johannes Weiner
Cc: Christoph Lameter
Cc: David Rientjes
Signed-off-by: Michal Hocko
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
With new refcounting we don't need to mark PMDs splitting. Let's drop
code to handle this.Signed-off-by: Kirill A. Shutemov
Tested-by: Sasha Levin
Tested-by: Aneesh Kumar K.V
Acked-by: Vlastimil Babka
Acked-by: Jerome Marchand
Cc: Andrea Arcangeli
Cc: Hugh Dickins
Cc: Dave Hansen
Cc: Mel Gorman
Cc: Rik van Riel
Cc: Naoya Horiguchi
Cc: Steve Capper
Cc: Johannes Weiner
Cc: Michal Hocko
Cc: Christoph Lameter
Cc: David Rientjes
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
With new refcounting we don't need to mark PMDs splitting. Let's drop
code to handle this.Signed-off-by: Kirill A. Shutemov
Tested-by: Sasha Levin
Acked-by: Jerome Marchand
Cc: Aneesh Kumar K.V
Cc: Vlastimil Babka
Cc: Andrea Arcangeli
Cc: Hugh Dickins
Cc: Dave Hansen
Cc: Mel Gorman
Cc: Rik van Riel
Cc: Naoya Horiguchi
Cc: Steve Capper
Cc: Johannes Weiner
Cc: Michal Hocko
Cc: Christoph Lameter
Cc: David Rientjes
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
With new refcounting we don't need to mark PMDs splitting. Let's drop
code to handle this.Signed-off-by: Kirill A. Shutemov
Cc: Sasha Levin
Cc: Aneesh Kumar K.V
Cc: Jerome Marchand
Cc: Vlastimil Babka
Cc: Andrea Arcangeli
Cc: Hugh Dickins
Cc: Dave Hansen
Cc: Mel Gorman
Cc: Rik van Riel
Cc: Naoya Horiguchi
Cc: Steve Capper
Cc: Johannes Weiner
Cc: Michal Hocko
Cc: Christoph Lameter
Cc: David Rientjes
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
With new refcounting we don't need to mark PMDs splitting. Let's drop
code to handle this.Signed-off-by: Kirill A. Shutemov
Cc: Sasha Levin
Cc: Aneesh Kumar K.V
Cc: Jerome Marchand
Cc: Vlastimil Babka
Cc: Andrea Arcangeli
Cc: Hugh Dickins
Cc: Dave Hansen
Cc: Mel Gorman
Cc: Rik van Riel
Cc: Naoya Horiguchi
Cc: Steve Capper
Cc: Johannes Weiner
Cc: Michal Hocko
Cc: Christoph Lameter
Cc: David Rientjes
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
With new refcounting we don't need to mark PMDs splitting. Let's drop
code to handle this.pmdp_splitting_flush() is not needed too: on splitting PMD we will do
pmdp_clear_flush() + set_pte_at(). pmdp_clear_flush() will do IPI as
needed for fast_gup.Signed-off-by: Kirill A. Shutemov
Cc: Sasha Levin
Cc: Aneesh Kumar K.V
Cc: Jerome Marchand
Cc: Vlastimil Babka
Cc: Andrea Arcangeli
Cc: Hugh Dickins
Cc: Dave Hansen
Cc: Mel Gorman
Cc: Rik van Riel
Cc: Naoya Horiguchi
Cc: Steve Capper
Cc: Johannes Weiner
Cc: Michal Hocko
Cc: Christoph Lameter
Cc: David Rientjes
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
With new refcounting we don't need to mark PMDs splitting. Let's drop
code to handle this.pmdp_splitting_flush() is not needed too: on splitting PMD we will do
pmdp_clear_flush() + set_pte_at(). pmdp_clear_flush() will do IPI as
needed for fast_gup.Signed-off-by: Kirill A. Shutemov
Tested-by: Aneesh Kumar K.V
Reviewed-by: Aneesh Kumar K.V
Cc: Sasha Levin
Cc: Jerome Marchand
Cc: Vlastimil Babka
Cc: Andrea Arcangeli
Cc: Hugh Dickins
Cc: Dave Hansen
Cc: Mel Gorman
Cc: Rik van Riel
Cc: Naoya Horiguchi
Cc: Steve Capper
Cc: Johannes Weiner
Cc: Michal Hocko
Cc: Christoph Lameter
Cc: David Rientjes
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
With new refcounting we don't need to mark PMDs splitting. Let's drop
code to handle this.pmdp_splitting_flush() is not needed too: on splitting PMD we will do
pmdp_clear_flush() + set_pte_at(). pmdp_clear_flush() will do IPI as
needed for fast_gup.Signed-off-by: Kirill A. Shutemov
Cc: Sasha Levin
Cc: Aneesh Kumar K.V
Cc: Jerome Marchand
Cc: Vlastimil Babka
Cc: Andrea Arcangeli
Cc: Hugh Dickins
Cc: Dave Hansen
Cc: Mel Gorman
Cc: Rik van Riel
Cc: Naoya Horiguchi
Cc: Steve Capper
Cc: Johannes Weiner
Cc: Michal Hocko
Cc: Christoph Lameter
Cc: David Rientjes
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
With new refcounting we don't need to mark PMDs splitting. Let's drop
code to handle this.pmdp_splitting_flush() is not needed too: on splitting PMD we will do
pmdp_clear_flush() + set_pte_at(). pmdp_clear_flush() will do IPI as
needed for fast_gup.[arnd@arndb.de: fix unterminated ifdef in header file]
Signed-off-by: Kirill A. Shutemov
Cc: Sasha Levin
Cc: Aneesh Kumar K.V
Cc: Jerome Marchand
Cc: Vlastimil Babka
Cc: Andrea Arcangeli
Cc: Hugh Dickins
Cc: Dave Hansen
Cc: Mel Gorman
Cc: Rik van Riel
Cc: Vlastimil Babka
Cc: Steve Capper
Cc: Johannes Weiner
Cc: Michal Hocko
Cc: Christoph Lameter
Cc: David Rientjes
Signed-off-by: Arnd Bergmann
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
With new refcounting we don't need to mark PMDs splitting. Let's drop
code to handle this.pmdp_splitting_flush() is not needed too: on splitting PMD we will do
pmdp_clear_flush() + set_pte_at(). pmdp_clear_flush() will do IPI as
needed for fast_gup.Signed-off-by: Kirill A. Shutemov
Cc: Sasha Levin
Cc: Aneesh Kumar K.V
Cc: Jerome Marchand
Cc: Vlastimil Babka
Cc: Andrea Arcangeli
Cc: Hugh Dickins
Cc: Dave Hansen
Cc: Mel Gorman
Cc: Rik van Riel
Cc: Naoya Horiguchi
Cc: Steve Capper
Cc: Johannes Weiner
Cc: Michal Hocko
Cc: Christoph Lameter
Cc: David Rientjes
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
We are going to use migration entries to stabilize page counts. It
means we don't need compound_lock() for that.Signed-off-by: Kirill A. Shutemov
Tested-by: Sasha Levin
Tested-by: Aneesh Kumar K.V
Acked-by: Vlastimil Babka
Acked-by: Jerome Marchand
Cc: Andrea Arcangeli
Cc: Hugh Dickins
Cc: Dave Hansen
Cc: Mel Gorman
Cc: Rik van Riel
Cc: Naoya Horiguchi
Cc: Steve Capper
Cc: Johannes Weiner
Cc: Michal Hocko
Cc: Christoph Lameter
Cc: David Rientjes
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
We don't need special code to stabilize THP. If you've got reference to
any subpage of THP it will not be split under you.New split_huge_page() also accepts tail pages: no need in special code
to get reference to head page.Signed-off-by: Kirill A. Shutemov
Tested-by: Sasha Levin
Tested-by: Aneesh Kumar K.V
Acked-by: Vlastimil Babka
Acked-by: Jerome Marchand
Cc: Andrea Arcangeli
Cc: Hugh Dickins
Cc: Dave Hansen
Cc: Mel Gorman
Cc: Rik van Riel
Cc: Naoya Horiguchi
Cc: Steve Capper
Cc: Johannes Weiner
Cc: Michal Hocko
Cc: Christoph Lameter
Cc: David Rientjes
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
With new THP refcounting, we don't need tricks to stabilize huge page.
If we've got reference to tail page, it can't split under us.This patch effectively reverts a5b338f2b0b1 ("thp: update futex compound
knowledge").Signed-off-by: Kirill A. Shutemov
Tested-by: Sasha Levin
Tested-by: Aneesh Kumar K.V
Acked-by: Jerome Marchand
Cc: Vlastimil Babka
Cc: Andrea Arcangeli
Cc: Hugh Dickins
Cc: Dave Hansen
Cc: Mel Gorman
Cc: Rik van Riel
Cc: Naoya Horiguchi
Cc: Steve Capper
Cc: Johannes Weiner
Cc: Michal Hocko
Cc: Christoph Lameter
Cc: David Rientjes
Tested-by: Artem Savkov
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
Tail page refcounting is utterly complicated and painful to support.
It uses ->_mapcount on tail pages to store how many times this page is
pinned. get_page() bumps ->_mapcount on tail page in addition to
->_count on head. This information is required by split_huge_page() to
be able to distribute pins from head of compound page to tails during
the split.We will need ->_mapcount to account PTE mappings of subpages of the
compound page. We eliminate need in current meaning of ->_mapcount in
tail pages by forbidding split entirely if the page is pinned.The only user of tail page refcounting is THP which is marked BROKEN for
now.Let's drop all this mess. It makes get_page() and put_page() much
simpler.Signed-off-by: Kirill A. Shutemov
Tested-by: Sasha Levin
Tested-by: Aneesh Kumar K.V
Acked-by: Vlastimil Babka
Acked-by: Jerome Marchand
Cc: Andrea Arcangeli
Cc: Hugh Dickins
Cc: Dave Hansen
Cc: Mel Gorman
Cc: Rik van Riel
Cc: Naoya Horiguchi
Cc: Steve Capper
Cc: Johannes Weiner
Cc: Michal Hocko
Cc: Christoph Lameter
Cc: David Rientjes
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
We will re-introduce new version with new refcounting later in patchset.
Signed-off-by: Kirill A. Shutemov
Tested-by: Sasha Levin
Tested-by: Aneesh Kumar K.V
Acked-by: Jerome Marchand
Cc: Vlastimil Babka
Cc: Andrea Arcangeli
Cc: Hugh Dickins
Cc: Dave Hansen
Cc: Mel Gorman
Cc: Rik van Riel
Cc: Naoya Horiguchi
Cc: Steve Capper
Cc: Johannes Weiner
Cc: Michal Hocko
Cc: Christoph Lameter
Cc: David Rientjes
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
Up to this point we tried to keep patchset bisectable, but next patches
are going to change how core of THP refcounting work.It would be beneficial to split the change into several patches and make
it more reviewable. Unfortunately, I don't see how we can achieve that
while keeping THP working.Let's hide THP under CONFIG_BROKEN for now and bring it back when new
refcounting get established.Signed-off-by: Kirill A. Shutemov
Tested-by: Sasha Levin
Tested-by: Aneesh Kumar K.V
Acked-by: Jerome Marchand
Cc: Vlastimil Babka
Cc: Andrea Arcangeli
Cc: Hugh Dickins
Cc: Dave Hansen
Cc: Mel Gorman
Cc: Rik van Riel
Cc: Naoya Horiguchi
Cc: Steve Capper
Cc: Johannes Weiner
Cc: Michal Hocko
Cc: Christoph Lameter
Cc: David Rientjes
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
The patch replaces THP_SPLIT with tree events: THP_SPLIT_PAGE,
THP_SPLIT_PAGE_FAILED and THP_SPLIT_PMD. It reflects the fact that we
are going to be able split PMD without the compound page and that
split_huge_page() can fail.Signed-off-by: Kirill A. Shutemov
Acked-by: Christoph Lameter
Tested-by: Sasha Levin
Tested-by: Aneesh Kumar K.V
Acked-by: Jerome Marchand
Acked-by: Vlastimil Babka
Cc: Andrea Arcangeli
Cc: Hugh Dickins
Cc: Dave Hansen
Cc: Mel Gorman
Cc: Rik van Riel
Cc: Naoya Horiguchi
Cc: Steve Capper
Cc: Johannes Weiner
Cc: Michal Hocko
Cc: David Rientjes
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
We are going to decouple splitting THP PMD from splitting underlying
compound page.This patch renames split_huge_page_pmd*() functions to split_huge_pmd*()
to reflect the fact that it doesn't imply page splitting, only PMD.Signed-off-by: Kirill A. Shutemov
Tested-by: Sasha Levin
Tested-by: Aneesh Kumar K.V
Acked-by: Jerome Marchand
Acked-by: Vlastimil Babka
Cc: Andrea Arcangeli
Cc: Hugh Dickins
Cc: Dave Hansen
Cc: Mel Gorman
Cc: Rik van Riel
Cc: Naoya Horiguchi
Cc: Steve Capper
Cc: Johannes Weiner
Cc: Michal Hocko
Cc: Christoph Lameter
Cc: David Rientjes
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
Prepare khugepaged to see compound pages mapped with pte. For now we
won't collapse the pmd table with such pte.khugepaged is subject for future rework wrt new refcounting.
Signed-off-by: Kirill A. Shutemov
Tested-by: Sasha Levin
Tested-by: Aneesh Kumar K.V
Acked-by: Jerome Marchand
Acked-by: Vlastimil Babka
Cc: Andrea Arcangeli
Cc: Hugh Dickins
Cc: Dave Hansen
Cc: Mel Gorman
Cc: Rik van Riel
Cc: Naoya Horiguchi
Cc: Steve Capper
Cc: Johannes Weiner
Cc: Michal Hocko
Cc: Christoph Lameter
Cc: David Rientjes
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
With new refcounting THP can belong to several VMAs. This makes tricky
to track THP pages, when they partially mlocked. It can lead to leaking
mlocked pages to non-VM_LOCKED vmas and other problems.With this patch we will split all pages on mlock and avoid
fault-in/collapse new THP in VM_LOCKED vmas.I've tried alternative approach: do not mark THP pages mlocked and keep
them on normal LRUs. This way vmscan could try to split huge pages on
memory pressure and free up subpages which doesn't belong to VM_LOCKED
vmas. But this is user-visible change: we screw up Mlocked accouting
reported in meminfo, so I had to leave this approach aside.We can bring something better later, but this should be good enough for
now.Signed-off-by: Kirill A. Shutemov
Tested-by: Sasha Levin
Tested-by: Aneesh Kumar K.V
Acked-by: Jerome Marchand
Cc: Vlastimil Babka
Cc: Andrea Arcangeli
Cc: Hugh Dickins
Cc: Dave Hansen
Cc: Mel Gorman
Cc: Rik van Riel
Cc: Naoya Horiguchi
Cc: Steve Capper
Cc: Johannes Weiner
Cc: Michal Hocko
Cc: Christoph Lameter
Cc: David Rientjes
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
With new refcounting we are going to see THP tail pages mapped with PTE.
Generic fast GUP rely on page_cache_get_speculative() to obtain
reference on page. page_cache_get_speculative() always fails on tail
pages, because ->_count on tail pages is always zero.Let's handle tail pages in gup_pte_range().
New split_huge_page() will rely on migration entries to freeze page's
counts. Recheck PTE value after page_cache_get_speculative() on head
page should be enough to serialize against split.Signed-off-by: Kirill A. Shutemov
Tested-by: Sasha Levin
Tested-by: Aneesh Kumar K.V
Acked-by: Jerome Marchand
Acked-by: Vlastimil Babka
Cc: Andrea Arcangeli
Cc: Hugh Dickins
Cc: Dave Hansen
Cc: Mel Gorman
Cc: Rik van Riel
Cc: Naoya Horiguchi
Cc: Steve Capper
Cc: Johannes Weiner
Cc: Michal Hocko
Cc: Christoph Lameter
Cc: David Rientjes
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
We need to prepare kernel to allow transhuge pages to be mapped with
ptes too. We need to handle FOLL_SPLIT in follow_page_pte().Also we use split_huge_page() directly instead of split_huge_page_pmd().
split_huge_page_pmd() will gone.Signed-off-by: Kirill A. Shutemov
Tested-by: Sasha Levin
Tested-by: Aneesh Kumar K.V
Acked-by: Vlastimil Babka
Acked-by: Jerome Marchand
Cc: Andrea Arcangeli
Cc: Hugh Dickins
Cc: Dave Hansen
Cc: Mel Gorman
Cc: Rik van Riel
Cc: Naoya Horiguchi
Cc: Steve Capper
Cc: Johannes Weiner
Cc: Michal Hocko
Cc: Christoph Lameter
Cc: David Rientjes
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
With new refcounting we will be able map the same compound page with
PTEs and PMDs. It requires adjustment to conditions when we can reuse
the page on write-protection fault.For PTE fault we can't reuse the page if it's part of huge page.
For PMD we can only reuse the page if nobody else maps the huge page or
it's part. We can do it by checking page_mapcount() on each sub-page,
but it's expensive.The cheaper way is to check page_count() to be equal 1: every mapcount
takes page reference, so this way we can guarantee, that the PMD is the
only mapping.This approach can give false negative if somebody pinned the page, but
that doesn't affect correctness.Signed-off-by: Kirill A. Shutemov
Tested-by: Sasha Levin
Tested-by: Aneesh Kumar K.V
Acked-by: Jerome Marchand
Acked-by: Vlastimil Babka
Cc: Andrea Arcangeli
Cc: Hugh Dickins
Cc: Dave Hansen
Cc: Mel Gorman
Cc: Rik van Riel
Cc: Naoya Horiguchi
Cc: Steve Capper
Cc: Johannes Weiner
Cc: Michal Hocko
Cc: Christoph Lameter
Cc: David Rientjes
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
As with rmap, with new refcounting we cannot rely on PageTransHuge() to
check if we need to charge size of huge page form the cgroup. We need
to get information from caller to know whether it was mapped with PMD or
PTE.We do uncharge when last reference on the page gone. At that point if
we see PageTransHuge() it means we need to unchange whole huge page.The tricky part is partial unmap -- when we try to unmap part of huge
page. We don't do a special handing of this situation, meaning we don't
uncharge the part of huge page unless last user is gone or
split_huge_page() is triggered. In case of cgroup memory pressure
happens the partial unmapped page will be split through shrinker. This
should be good enough.Signed-off-by: Kirill A. Shutemov
Tested-by: Sasha Levin
Tested-by: Aneesh Kumar K.V
Acked-by: Vlastimil Babka
Acked-by: Jerome Marchand
Cc: Andrea Arcangeli
Cc: Hugh Dickins
Cc: Dave Hansen
Cc: Mel Gorman
Cc: Rik van Riel
Cc: Naoya Horiguchi
Cc: Steve Capper
Cc: Johannes Weiner
Cc: Michal Hocko
Cc: Christoph Lameter
Cc: David Rientjes
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
We're going to allow mapping of individual 4k pages of THP compound
page. It means we cannot rely on PageTransHuge() check to decide if
map/unmap small page or THP.The patch adds new argument to rmap functions to indicate whether we
want to operate on whole compound page or only the small page.[n-horiguchi@ah.jp.nec.com: fix mapcount mismatch in hugepage migration]
Signed-off-by: Kirill A. Shutemov
Tested-by: Sasha Levin
Tested-by: Aneesh Kumar K.V
Acked-by: Vlastimil Babka
Acked-by: Jerome Marchand
Cc: Andrea Arcangeli
Cc: Hugh Dickins
Cc: Dave Hansen
Cc: Mel Gorman
Cc: Rik van Riel
Cc: Steve Capper
Cc: Johannes Weiner
Cc: Michal Hocko
Cc: Christoph Lameter
Cc: David Rientjes
Signed-off-by: Naoya Horiguchi
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds -
The goal of this patchset is to make refcounting on THP pages cheaper
with simpler semantics and allow the same THP compound page to be mapped
with PMD and PTEs. This is required to get reasonable THP-pagecache
implementation.With the new refcounting design it's much easier to protect against
split_huge_page(): simple reference on a page will make you the deal.
It makes gup_fast() implementation simpler and doesn't require
special-case in futex code to handle tail THP pages.It should improve THP utilization over the system since splitting THP in
one process doesn't necessary lead to splitting the page in all other
processes have the page mapped.The patchset drastically lower complexity of get_page()/put_page()
codepaths. I encourage people look on this code before-and-after to
justify time budget on reviewing this patchset.This patch (of 37):
With new refcounting all subpages of the compound page are not necessary
have the same mapcount. We need to take into account mapcount of every
sub-page.Signed-off-by: Kirill A. Shutemov
Tested-by: Sasha Levin
Tested-by: Aneesh Kumar K.V
Acked-by: Jerome Marchand
Acked-by: Vlastimil Babka
Cc: Andrea Arcangeli
Cc: Hugh Dickins
Cc: Dave Hansen
Cc: Mel Gorman
Cc: Rik van Riel
Cc: Naoya Horiguchi
Cc: Steve Capper
Cc: Johannes Weiner
Cc: Michal Hocko
Cc: Christoph Lameter
Cc: David Rientjes
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds
