> From: Michal Hocko <[email protected]>
>
> Joonsoo has reported that he is able to trigger OOM for !costly high
> order requests (heavy fork() workload close the OOM) with the new
> oom detection rework. This is because we rely only on should_reclaim_retry
> when the compaction is disabled and it only checks watermarks for the
> requested order and so we might trigger OOM when there is a lot of free
> memory.
>
> It is not very clear what are the usual workloads when the compaction
> is disabled. Relying on high order allocations heavily without any
> mechanism to create those orders except for unbound amount of reclaim is
> certainly not a good idea.
>
> To prevent from potential regressions let's help this configuration
> some. We have to sacrifice the determinsm though because there simply is
> none here possible. should_compact_retry implementation for
> !CONFIG_COMPACTION, which was empty so far, will do watermark check
> for order-0 on all eligible zones. This will cause retrying until either
> the reclaim cannot make any further progress or all the zones are
> depleted even for order-0 pages. This means that the number of retries
> is basically unbounded for !costly orders but that was the case before
> the rework as well so this shouldn't regress.
>
> Reported-by: Joonsoo Kim <[email protected]>
> Signed-off-by: Michal Hocko <[email protected]>
> ---
Acked-by: Hillf Danton <[email protected]>
> mm/page_alloc.c | 18 ++++++++++++++++++
> 1 file changed, 18 insertions(+)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 620ec002aea2..7e2defbfe55b 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -3310,6 +3310,24 @@ should_compact_retry(struct alloc_context *ac,
> unsigned int order, int alloc_fla
> enum migrate_mode *migrate_mode,
> int compaction_retries)
> {
> + struct zone *zone;
> + struct zoneref *z;
> +
> + if (!order || order > PAGE_ALLOC_COSTLY_ORDER)
> + return false;
> +
> + /*
> + * There are setups with compaction disabled which would prefer to loop
> + * inside the allocator rather than hit the oom killer prematurely.
> Let's
> + * give them a good hope and keep retrying while the order-0 watermarks
> + * are OK.
> + */
> + for_each_zone_zonelist_nodemask(zone, z, ac->zonelist, ac->high_zoneidx,
> + ac->nodemask) {
> + if(zone_watermark_ok(zone, 0, min_wmark_pages(zone),
s/if(zone_/if (zone_/
> + ac_classzone_idx(ac), alloc_flags))
> + return true;
> + }
> return false;
> }
> #endif /* CONFIG_COMPACTION */
> --
> 2.8.1
