On 2/12/21 6:33 PM, Charan Teja Reddy wrote: > 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. > > Signed-off-by: Charan Teja Reddy <charante@xxxxxxxxxxxxxx> Acked-by: Vlastimil Babka <vbabka@xxxxxxx> Thanks! > --- > > changes in V1: https://lore.kernel.org/patchwork/patch/1373665/ > > mm/compaction.c | 8 ++++++++ > mm/page_alloc.c | 2 ++ > 2 files changed, 10 insertions(+) > > diff --git a/mm/compaction.c b/mm/compaction.c > index 190ccda..104ebef 100644 > --- a/mm/compaction.c > +++ b/mm/compaction.c > @@ -2487,6 +2487,14 @@ static enum compact_result compact_zone_order(struct zone *zone, int order, > */ > 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; > } > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 519a60d..531f244 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -4152,6 +4152,8 @@ __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order, > 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 >
