From: Charan Teja Reddy <charante@xxxxxxxxxxxxxx> Subject: mm: compaction: update the COMPACT[STALL|FAIL] events properly By definition, COMPACT[STALL|FAIL] events needs to be counted when there is 'At least in one zone compaction wasn't deferred or skipped from the direct compaction'. And when compaction is skipped or deferred, COMPACT_SKIPPED will be returned but it will still go and update these compaction events which is wrong in the sense that COMPACT[STALL|FAIL] is counted without even trying the compaction. Correct this by skipping the counting of these events when COMPACT_SKIPPED is returned for compaction. This indirectly also avoid the unnecessary try into the get_page_from_freelist() when compaction is not even tried. There is a corner case where compaction is skipped but still count COMPACTSTALL event, which is that IRQ came and freed the page and the same is captured in capture_control. Link: https://lkml.kernel.org/r/1613151184-21213-1-git-send-email-charante@xxxxxxxxxxxxxx Signed-off-by: Charan Teja Reddy <charante@xxxxxxxxxxxxxx> Acked-by: Vlastimil Babka <vbabka@xxxxxxx> Acked-by: David Rientjes <rientjes@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/compaction.c | 8 ++++++++ mm/page_alloc.c | 2 ++ 2 files changed, 10 insertions(+) --- a/mm/compaction.c~mm-compaction-update-the-compact-events-properly +++ a/mm/compaction.c @@ -2529,6 +2529,14 @@ static enum compact_result compact_zone_ */ WRITE_ONCE(current->capture_control, NULL); *capture = READ_ONCE(capc.page); + /* + * Technically, it is also possible that compaction is skipped but + * the page is still captured out of luck(IRQ came and freed the page). + * Returning COMPACT_SUCCESS in such cases helps in properly accounting + * the COMPACT[STALL|FAIL] when compaction is skipped. + */ + if (*capture) + ret = COMPACT_SUCCESS; return ret; } --- a/mm/page_alloc.c~mm-compaction-update-the-compact-events-properly +++ a/mm/page_alloc.c @@ -4204,6 +4204,8 @@ __alloc_pages_direct_compact(gfp_t gfp_m memalloc_noreclaim_restore(noreclaim_flag); psi_memstall_leave(&pflags); + if (*compact_result == COMPACT_SKIPPED) + return NULL; /* * At least in one zone compaction wasn't deferred or skipped, so let's * count a compaction stall _
