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mm: compaction: include compound page count for scanning in pageblock isolation

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The number of scanned pages can be lower than the number of isolated pages
when isolating mirgratable or free pageblock.  The metric is being
reported in trace event and also used in vmstat.

some example output from trace where it shows nr_taken can be greater
than nr_scanned:

Produced by kernel v5.19-rc6
kcompactd0-42      [001] .....  1210.268022: mm_compaction_isolate_migratepages: range=(0x107ae4 ~ 0x107c00) nr_scanned=265 nr_taken=255
[...]
kcompactd0-42      [001] .....  1210.268382: mm_compaction_isolate_freepages: range=(0x215800 ~ 0x215a00) nr_scanned=13 nr_taken=128
kcompactd0-42      [001] .....  1210.268383: mm_compaction_isolate_freepages: range=(0x215600 ~ 0x215680) nr_scanned=1 nr_taken=128

mm_compaction_isolate_migratepages does not seem to have this
behaviour, but for the reason of consistency, nr_scanned should also be
taken care of in that side.

This behaviour is confusing since currently the count for isolated pages
takes account of compound page but not for the case of scanned pages.  And
given that the number of isolated pages(nr_taken) reported in
mm_compaction_isolate_template trace event is on a single-page basis, the
ambiguity when reporting the number of scanned pages can be removed by
also including compound page count.

Link: https://lkml.kernel.org/r/20220711202806.22296-1-william.lam@bytedance.com
Signed-off-by: William Lam <william.lam@bytedance.com>
Reviewed-by: Punit Agrawal <punit.agrawal@bytedance.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
William Lam 2022-07-11 21:28:06 +01:00 committed by akpm
parent ac3ced5fc1
commit b717d6b93b
1 changed files with 3 additions and 0 deletions
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3
mm/compaction.c
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@ -616,6 +616,7 @@ static unsigned long isolate_freepages_block(struct compact_control *cc,
break;
set_page_private(page, order);
nr_scanned += isolated - 1;
total_isolated += isolated;
cc->nr_freepages += isolated;
list_add_tail(&page->lru, freelist);
@ -1101,6 +1102,7 @@ isolate_success:
isolate_success_no_list:
cc->nr_migratepages += compound_nr(page);
nr_isolated += compound_nr(page);
nr_scanned += compound_nr(page) - 1;
/*
* Avoid isolating too much unless this block is being
@ -1504,6 +1506,7 @@ fast_isolate_freepages(struct compact_control *cc)
if (__isolate_free_page(page, order)) {
set_page_private(page, order);
nr_isolated = 1 << order;
nr_scanned += nr_isolated - 1;
cc->nr_freepages += nr_isolated;
list_add_tail(&page->lru, &cc->freepages);
count_compact_events(COMPACTISOLATED, nr_isolated);