Eric Lee / smarc-ti-linux-kernel

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Commit 8fdb3dbf02335d96bf170321381522709ba63a0c

Authored by Hugh Dickins
Committed by Linus Torvalds
1 parent 49cd0a5c29
Exists in master and in 20 other branches dlt-processor-sdk-linux-03.00.00.04, newt-ti-linux-3.12.y, processor-sdk-linux-01.00.00, processor-sdk-linux-02.00.01, smarc-ti-linux-3.12.10, smarc-ti-linux-3.12.y, smarc-ti-linux-3.14.y, smarc-ti-linux-3.15.y, smarc-ti-lsk-linux-4.1.y, smarct3x-processor-sdk-04.01.00.06, smarct3x-processor-sdk-linux-02.00.01, smarct3x-processor-sdk-linux-03.00.00.04, smarct4x-800-processor-sdk-linux-02.00.01, smarct4x-processor-sdk-04.01.00.06, smarct4x-processor-sdk-linux-02.00.01, smarct4x-processor-sdk-linux-03.00.00.04, ti-linux-3.12.y, ti-linux-3.14.y, ti-linux-3.15.y, ti-lsk-linux-4.1.y

ksm: add some comments 

Added slightly more detail to the Documentation of merge_across_nodes, a
few comments in areas indicated by review, and renamed get_ksm_page()'s
argument from "locked" to "lock_it".  No functional change.

Signed-off-by: Hugh Dickins <hughd@google.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Petr Holasek <pholasek@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Izik Eidus <izik.eidus@ravellosystems.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Showing 2 changed files with 26 additions and 8 deletions Side-by-side Diff

Documentation/vm/ksm.txt
Diff comments   View file @ 8fdb3db
... ... @@ -60,10 +60,18 @@
60 60  
61 61 merge_across_nodes - specifies if pages from different numa nodes can be merged.
62 62 When set to 0, ksm merges only pages which physically
63   - reside in the memory area of same NUMA node. It brings
64   - lower latency to access to shared page. Value can be
65   - changed only when there is no ksm shared pages in system.
66   - Default: 1
  63 + reside in the memory area of same NUMA node. That brings
  64 + lower latency to access of shared pages. Systems with more
  65 + nodes, at significant NUMA distances, are likely to benefit
  66 + from the lower latency of setting 0. Smaller systems, which
  67 + need to minimize memory usage, are likely to benefit from
  68 + the greater sharing of setting 1 (default). You may wish to
  69 + compare how your system performs under each setting, before
  70 + deciding on which to use. merge_across_nodes setting can be
  71 + changed only when there are no ksm shared pages in system:
  72 + set run 2 to unmerge pages first, then to 1 after changing
  73 + merge_across_nodes, to remerge according to the new setting.
  74 + Default: 1 (merging across nodes as in earlier releases)
67 75  
68 76 run - set 0 to stop ksmd from running but keep merged pages,
69 77 set 1 to run ksmd e.g. "echo 1 > /sys/kernel/mm/ksm/run",
... ... @@ -87,6 +87,9 @@
87 87 * take 10 attempts to find a page in the unstable tree, once it is found,
88 88 * it is secured in the stable tree. (When we scan a new page, we first
89 89 * compare it against the stable tree, and then against the unstable tree.)
  90 + *
  91 + * If the merge_across_nodes tunable is unset, then KSM maintains multiple
  92 + * stable trees and multiple unstable trees: one of each for each NUMA node.
90 93 */
91 94  
92 95 /**
... ... @@ -526,7 +529,7 @@
526 529 * a page to put something that might look like our key in page->mapping.
527 530 * is on its way to being freed; but it is an anomaly to bear in mind.
528 531 */
529   -static struct page *get_ksm_page(struct stable_node *stable_node, bool locked)
  532 +static struct page *get_ksm_page(struct stable_node *stable_node, bool lock_it)
530 533 {
531 534 struct page *page;
532 535 void *expected_mapping;
... ... @@ -575,7 +578,7 @@
575 578 goto stale;
576 579 }
577 580  
578   - if (locked) {
  581 + if (lock_it) {
579 582 lock_page(page);
580 583 if (ACCESS_ONCE(page->mapping) != expected_mapping) {
581 584 unlock_page(page);
582 585  
583 586  
... ... @@ -705,10 +708,17 @@
705 708 return 0;
706 709 }
707 710  
708   - if (WARN_ON_ONCE(page_mapped(page)))
  711 + if (WARN_ON_ONCE(page_mapped(page))) {
  712 + /*
  713 + * This should not happen: but if it does, just refuse to let
  714 + * merge_across_nodes be switched - there is no need to panic.
  715 + */
709 716 err = -EBUSY;
710   - else {
  717 + } else {
711 718 /*
  719 + * The stable node did not yet appear stale to get_ksm_page(),
  720 + * since that allows for an unmapped ksm page to be recognized
  721 + * right up until it is freed; but the node is safe to remove.
712 722 * This page might be in a pagevec waiting to be freed,
713 723 * or it might be PageSwapCache (perhaps under writeback),
714 724 * or it might have been removed from swapcache a moment ago.