>
> From: Michal Hocko <mhocko@xxxxxxxx>
>
> __alloc_pages_direct_compact communicates potential back off by two
> variables:
> - deferred_compaction tells that the compaction returned
> COMPACT_DEFERRED
> - contended_compaction is set when there is a contention on
> zone->lock resp. zone->lru_lock locks
>
> __alloc_pages_slowpath then backs of for THP allocation requests to
> prevent from long stalls. This is rather messy and it would be much
> cleaner to return a single compact result value and hide all the nasty
> details into __alloc_pages_direct_compact.
>
> This patch shouldn't introduce any functional changes.
>
> Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
> Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
> ---
Acked-by: Hillf Danton <hillf.zj@xxxxxxxxxxxxxxx>
> mm/page_alloc.c | 67 ++++++++++++++++++++++++++-------------------------------
> 1 file changed, 31 insertions(+), 36 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 06af8a757d52..350d13f3709b 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -2944,29 +2944,21 @@ __alloc_pages_may_oom(gfp_t gfp_mask, unsigned int order,
> static struct page *
> __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order,
> int alloc_flags, const struct alloc_context *ac,
> - enum migrate_mode mode, int *contended_compaction,
> - bool *deferred_compaction)
> + enum migrate_mode mode, enum compact_result *compact_result)
> {
> - enum compact_result compact_result;
> struct page *page;
> + int contended_compaction;
>
> if (!order)
> return NULL;
>
> current->flags |= PF_MEMALLOC;
> - compact_result = try_to_compact_pages(gfp_mask, order, alloc_flags, ac,
> - mode, contended_compaction);
> + *compact_result = try_to_compact_pages(gfp_mask, order, alloc_flags, ac,
> + mode, &contended_compaction);
> current->flags &= ~PF_MEMALLOC;
>
> - switch (compact_result) {
> - case COMPACT_DEFERRED:
> - *deferred_compaction = true;
> - /* fall-through */
> - case COMPACT_SKIPPED:
> + if (*compact_result <= COMPACT_INACTIVE)
> return NULL;
> - default:
> - break;
> - }
>
> /*
> * At least in one zone compaction wasn't deferred or skipped, so let's
> @@ -2992,6 +2984,24 @@ __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order,
> */
> count_vm_event(COMPACTFAIL);
>
> + /*
> + * In all zones where compaction was attempted (and not
> + * deferred or skipped), lock contention has been detected.
> + * For THP allocation we do not want to disrupt the others
> + * so we fallback to base pages instead.
> + */
> + if (contended_compaction == COMPACT_CONTENDED_LOCK)
> + *compact_result = COMPACT_CONTENDED;
> +
> + /*
> + * If compaction was aborted due to need_resched(), we do not
> + * want to further increase allocation latency, unless it is
> + * khugepaged trying to collapse.
> + */
> + if (contended_compaction == COMPACT_CONTENDED_SCHED
> + && !(current->flags & PF_KTHREAD))
> + *compact_result = COMPACT_CONTENDED;
> +
> cond_resched();
>
> return NULL;
> @@ -3000,8 +3010,7 @@ __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order,
> static inline struct page *
> __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order,
> int alloc_flags, const struct alloc_context *ac,
> - enum migrate_mode mode, int *contended_compaction,
> - bool *deferred_compaction)
> + enum migrate_mode mode, enum compact_result *compact_result)
> {
> return NULL;
> }
> @@ -3146,8 +3155,7 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
> unsigned long pages_reclaimed = 0;
> unsigned long did_some_progress;
> enum migrate_mode migration_mode = MIGRATE_ASYNC;
> - bool deferred_compaction = false;
> - int contended_compaction = COMPACT_CONTENDED_NONE;
> + enum compact_result compact_result;
>
> /*
> * In the slowpath, we sanity check order to avoid ever trying to
> @@ -3245,8 +3253,7 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
> */
> page = __alloc_pages_direct_compact(gfp_mask, order, alloc_flags, ac,
> migration_mode,
> - &contended_compaction,
> - &deferred_compaction);
> + &compact_result);
> if (page)
> goto got_pg;
>
> @@ -3259,25 +3266,14 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
> * to heavily disrupt the system, so we fail the allocation
> * instead of entering direct reclaim.
> */
> - if (deferred_compaction)
> - goto nopage;
> -
> - /*
> - * In all zones where compaction was attempted (and not
> - * deferred or skipped), lock contention has been detected.
> - * For THP allocation we do not want to disrupt the others
> - * so we fallback to base pages instead.
> - */
> - if (contended_compaction == COMPACT_CONTENDED_LOCK)
> + if (compact_result == COMPACT_DEFERRED)
> goto nopage;
>
> /*
> - * If compaction was aborted due to need_resched(), we do not
> - * want to further increase allocation latency, unless it is
> - * khugepaged trying to collapse.
> + * Compaction is contended so rather back off than cause
> + * excessive stalls.
> */
> - if (contended_compaction == COMPACT_CONTENDED_SCHED
> - && !(current->flags & PF_KTHREAD))
> + if(compact_result == COMPACT_CONTENDED)
> goto nopage;
> }
>
> @@ -3325,8 +3321,7 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
> */
> page = __alloc_pages_direct_compact(gfp_mask, order, alloc_flags,
> ac, migration_mode,
> - &contended_compaction,
> - &deferred_compaction);
> + &compact_result);
> if (page)
> goto got_pg;
> nopage:
> --
> 2.8.0.rc3
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