On 03/07/2016 05:08 PM, Michal Hocko wrote:
> On Mon 29-02-16 22:02:13, Michal Hocko wrote:
>> Andrew,
>> could you queue this one as well, please? This is more a band aid than a
>> real solution which I will be working on as soon as I am able to
>> reproduce the issue but the patch should help to some degree at least.
>
> Joonsoo wasn't very happy about this approach so let me try a different
> way. What do you think about the following? Hugh, Sergey does it help
> for your load? I have tested it with the Hugh's load and there was no
> major difference from the previous testing so at least nothing has blown
> up as I am not able to reproduce the issue here.
>
> Other changes in the compaction are still needed but I would like to not
> depend on them right now.
> ---
> From 0974f127e8eb7fe53e65f3a8b398db57effe9755 Mon Sep 17 00:00:00 2001
> From: Michal Hocko <mho...@suse.com>
> Date: Mon, 7 Mar 2016 15:30:37 +0100
> Subject: [PATCH] mm, oom: protect !costly allocations some more
>
> should_reclaim_retry will give up retries for higher order allocations
> if none of the eligible zones has any requested or higher order pages
> available even if we pass the watermak check for order-0. This is done
> because there is no guarantee that the reclaimable and currently free
> pages will form the required order.
>
> This can, however, lead to situations were the high-order request (e.g.
> order-2 required for the stack allocation during fork) will trigger
> OOM too early - e.g. after the first reclaim/compaction round. Such a
> system would have to be highly fragmented and there is no guarantee
> further reclaim/compaction attempts would help but at least make sure
> that the compaction was active before we go OOM and keep retrying even
> if should_reclaim_retry tells us to oom if the last compaction round
> was either inactive (deferred, skipped or bailed out early due to
> contention) or it told us to continue.
>
> Additionally define COMPACT_NONE which reflects cases where the
> compaction is completely disabled.
>
> Signed-off-by: Michal Hocko <mho...@suse.com>
> ---
> include/linux/compaction.h | 2 ++
> mm/page_alloc.c | 41 ++++++++++++++++++++++++-----------------
> 2 files changed, 26 insertions(+), 17 deletions(-)
>
> diff --git a/include/linux/compaction.h b/include/linux/compaction.h
> index 4cd4ddf64cc7..a4cec4a03f7d 100644
> --- a/include/linux/compaction.h
> +++ b/include/linux/compaction.h
> @@ -1,6 +1,8 @@
> #ifndef _LINUX_COMPACTION_H
> #define _LINUX_COMPACTION_H
>
> +/* compaction disabled */
> +#define COMPACT_NONE -1
> /* Return values for compact_zone() and try_to_compact_pages() */
> /* compaction didn't start as it was deferred due to past failures */
> #define COMPACT_DEFERRED 0
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 269a04f20927..f89e3cbfdf90 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -2819,28 +2819,22 @@ 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)
> + unsigned long *compact_result)
> {
> - unsigned long compact_result;
> struct page *page;
>
> - if (!order)
> + if (!order) {
> + *compact_result = COMPACT_NONE;
> return NULL;
> + }
>
> current->flags |= PF_MEMALLOC;
> - compact_result = try_to_compact_pages(gfp_mask, order, alloc_flags, ac,
> + *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_SKIPPED)
COMPACT_NONE is -1 and compact_result is unsigned long, so this won't
work as expected.
> return NULL;
> - default:
> - break;
> - }
>
> /*
> * At least in one zone compaction wasn't deferred or skipped, so let's
> @@ -2875,8 +2869,9 @@ 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)
> + unsigned long *compact_result)
> {
> + *compact_result = COMPACT_NONE;
> return NULL;
> }
> #endif /* CONFIG_COMPACTION */
> @@ -3118,7 +3113,7 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int
> order,
> int alloc_flags;
> unsigned long did_some_progress;
> enum migrate_mode migration_mode = MIGRATE_ASYNC;
> - bool deferred_compaction = false;
> + unsigned long compact_result;
> int contended_compaction = COMPACT_CONTENDED_NONE;
> int no_progress_loops = 0;
>
> @@ -3227,7 +3222,7 @@ __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;
>
> @@ -3240,7 +3235,7 @@ __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)
> + if (compact_result == COMPACT_DEFERRED)
> goto nopage;
>
> /*
> @@ -3294,6 +3289,18 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int
> order,
> did_some_progress > 0, no_progress_loops))
> goto retry;
>
> + /*
> + * !costly allocations are really important and we have to make sure
> + * the compaction wasn't deferred or didn't bail out early due to locks
> + * contention before we go OOM.
> + */
> + if (order && order <= PAGE_ALLOC_COSTLY_ORDER) {
> + if (compact_result <= COMPACT_CONTINUE)
Same here.
I was going to say that this didn't have effect on Sergey's test, but
turns out it did :)
> + goto retry;
> + if (contended_compaction > COMPACT_CONTENDED_NONE)
> + goto retry;
> + }
> +
> /* Reclaim has failed us, start killing things */
> page = __alloc_pages_may_oom(gfp_mask, order, ac, &did_some_progress);
> if (page)
> @@ -3314,7 +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:
>
