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Date: Tue, 19 Jul 2016 15:50:24 -0700 (PDT)
From: David Rientjes <rientjes@...gle.com>
To: Vlastimil Babka <vbabka@...e.cz>
cc: Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org, Michal Hocko <mhocko@...nel.org>,
Mel Gorman <mgorman@...hsingularity.net>,
Joonsoo Kim <iamjoonsoo.kim@....com>,
Rik van Riel <riel@...hat.com>
Subject: Re: [PATCH 4/8] mm, page_alloc: restructure direct compaction handling
in slowpath
On Mon, 18 Jul 2016, Vlastimil Babka wrote:
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 30443804f156..a04a67745927 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -3510,7 +3510,7 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
> struct page *page = NULL;
> unsigned int alloc_flags;
> unsigned long did_some_progress;
> - enum migrate_mode migration_mode = MIGRATE_ASYNC;
> + enum migrate_mode migration_mode = MIGRATE_SYNC_LIGHT;
> enum compact_result compact_result;
> int compaction_retries = 0;
> int no_progress_loops = 0;
> @@ -3552,6 +3552,49 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
> if (page)
> goto got_pg;
>
> + /*
> + * For costly allocations, try direct compaction first, as it's likely
> + * that we have enough base pages and don't need to reclaim.
> + */
> + if (can_direct_reclaim && order > PAGE_ALLOC_COSTLY_ORDER) {
> + page = __alloc_pages_direct_compact(gfp_mask, order,
> + alloc_flags, ac,
> + MIGRATE_ASYNC,
> + &compact_result);
> + if (page)
> + goto got_pg;
> +
> + /* Checks for THP-specific high-order allocations */
> + if (is_thp_gfp_mask(gfp_mask)) {
> + /*
> + * If compaction is deferred for high-order allocations,
> + * it is because sync compaction recently failed. If
> + * this is the case and the caller requested a THP
> + * allocation, we do not want to heavily disrupt the
> + * system, so we fail the allocation instead of entering
> + * direct reclaim.
> + */
> + if (compact_result == COMPACT_DEFERRED)
> + goto nopage;
> +
> + /*
> + * Compaction is contended so rather back off than cause
> + * excessive stalls.
> + */
> + if (compact_result == COMPACT_CONTENDED)
> + goto nopage;
> +
> + /*
> + * It can become very expensive to allocate transparent
> + * hugepages at fault, so use asynchronous memory
> + * compaction for THP unless it is khugepaged trying to
> + * collapse. All other requests should tolerate at
> + * least light sync migration.
> + */
> + if (!(current->flags & PF_KTHREAD))
> + migration_mode = MIGRATE_ASYNC;
> + }
> + }
>
If gfp_pfmemalloc_allowed() == true, does this try to do compaction when
get_page_from_freelist() would have succeeded with no watermarks?
> retry:
> /* Ensure kswapd doesn't accidentally go to sleep as long as we loop */
> @@ -3606,55 +3649,33 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
> if (test_thread_flag(TIF_MEMDIE) && !(gfp_mask & __GFP_NOFAIL))
> goto nopage;
>
> - /*
> - * Try direct compaction. The first pass is asynchronous. Subsequent
> - * attempts after direct reclaim are synchronous
> - */
> +
> + /* Try direct reclaim and then allocating */
> + page = __alloc_pages_direct_reclaim(gfp_mask, order, alloc_flags, ac,
> + &did_some_progress);
> + if (page)
> + goto got_pg;
> +
> + /* Try direct compaction and then allocating */
> page = __alloc_pages_direct_compact(gfp_mask, order, alloc_flags, ac,
> migration_mode,
> &compact_result);
> if (page)
> goto got_pg;
>
> - /* Checks for THP-specific high-order allocations */
> - if (is_thp_gfp_mask(gfp_mask)) {
> - /*
> - * If compaction is deferred for high-order allocations, it is
> - * because sync compaction recently failed. If this is the case
> - * and the caller requested a THP allocation, we do not want
> - * to heavily disrupt the system, so we fail the allocation
> - * instead of entering direct reclaim.
> - */
> - if (compact_result == COMPACT_DEFERRED)
> - goto nopage;
> -
> - /*
> - * Compaction is contended so rather back off than cause
> - * excessive stalls.
> - */
> - if(compact_result == COMPACT_CONTENDED)
> - goto nopage;
> - }
> -
> if (order && compaction_made_progress(compact_result))
> compaction_retries++;
>
> - /* Try direct reclaim and then allocating */
> - page = __alloc_pages_direct_reclaim(gfp_mask, order, alloc_flags, ac,
> - &did_some_progress);
> - if (page)
> - goto got_pg;
> -
> /* Do not loop if specifically requested */
> if (gfp_mask & __GFP_NORETRY)
> - goto noretry;
> + goto nopage;
>
> /*
> * Do not retry costly high order allocations unless they are
> * __GFP_REPEAT
> */
> if (order > PAGE_ALLOC_COSTLY_ORDER && !(gfp_mask & __GFP_REPEAT))
> - goto noretry;
> + goto nopage;
>
> /*
> * Costly allocations might have made a progress but this doesn't mean
> @@ -3693,25 +3714,6 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
> goto retry;
> }
>
> -noretry:
> - /*
> - * High-order allocations do not necessarily loop after direct reclaim
> - * and reclaim/compaction depends on compaction being called after
> - * reclaim so call directly if necessary.
> - * It can become very expensive to allocate transparent hugepages at
> - * fault, so use asynchronous memory compaction for THP unless it is
> - * khugepaged trying to collapse. All other requests should tolerate
> - * at least light sync migration.
> - */
> - if (is_thp_gfp_mask(gfp_mask) && !(current->flags & PF_KTHREAD))
> - migration_mode = MIGRATE_ASYNC;
> - else
> - migration_mode = MIGRATE_SYNC_LIGHT;
> - page = __alloc_pages_direct_compact(gfp_mask, order, alloc_flags,
> - ac, migration_mode,
> - &compact_result);
> - if (page)
> - goto got_pg;
> nopage:
> warn_alloc_failed(gfp_mask, order, NULL);
> got_pg:
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