linux-kernel - Re: mm, vmscan: commit makes PAE kernel crash nightly (bisected)

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Date:   Wed, 25 Jan 2017 10:46:37 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Mel Gorman <mgorman@...hsingularity.net>
Cc:     Trevor Cordes <trevor@...nopolis.ca>, linux-kernel@...r.kernel.org,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Minchan Kim <minchan@...nel.org>,
        Rik van Riel <riel@...riel.com>,
        Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Subject: Re: mm, vmscan: commit makes PAE kernel crash nightly (bisected)

On Mon 23-01-17 11:04:12, Mel Gorman wrote:
[...]
> 1. In should_reclaim_retry, account for SLAB_RECLAIMABLE as available
>    pages when deciding to retry reclaim

I am pretty sure I have considered this but then decided to not go that
way. I do not remember details so I will think about this some more. It
might have been just "let's wait for the real issue here". Anyway we can
give it a try and it would be as simple as
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 94ebd30d0f09..87221491be84 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3566,7 +3566,7 @@ should_reclaim_retry(gfp_t gfp_mask, unsigned order,
 		unsigned long min_wmark = min_wmark_pages(zone);
 		bool wmark;
 
-		available = reclaimable = zone_reclaimable_pages(zone);
+		available = reclaimable = zone_reclaimable_pages(zone) + zone_page_state_snapshot(zone, NR_SLAB_RECLAIMABLE);
 		available -= DIV_ROUND_UP((*no_progress_loops) * available,
 					  MAX_RECLAIM_RETRIES);
 		available += zone_page_state_snapshot(zone, NR_FREE_PAGES);

I am not sure it would really help much on its own without further
changes to how we scale LRU->slab scanning. Could you give this a try
on top of the mmotm or linux-next tree?

> 2. Stall in should_reclaim_retry for __GFP_NOFAIL|__GFP_NOFS with a
>    comment stating that the intent is to allow kswapd make progress
>    with the shrinker

The current mmotm tree doesnt need this because we no longer trigger the
oom killer for this combinations of flags.

> 3. Stall __GFP_NOFS in direct reclaimer on a workqueue when it's
>    failing to make progress to allow kswapd to do some work. This
>    may be impaired if kswapd is locked up waiting for a lock held
>    by the direct reclaimer
> 4. Schedule the system workqueue to drain slab for
>    __GFP_NOFS|__GFP_NOFAIL.
> 
> 3 and 4 are extremely heavy handed so we should try them one at a time.

I am not even sure they are really necessary.
-- 
Michal Hocko
SUSE Labs