On Mon, Feb 27, 2017 at 10:44:49AM +0100, Michal Hocko wrote:
> On Mon 27-02-17 18:02:36, Minchan Kim wrote:
> [...]
> > >From 9779a1c5d32e2edb64da5cdfcd6f9737b94a247a Mon Sep 17 00:00:00 2001
> > From: Minchan Kim <minchan@xxxxxxxxxx>
> > Date: Mon, 27 Feb 2017 17:39:06 +0900
> > Subject: [PATCH] mm: use up highatomic before OOM kill
> >
> > Not-Yet-Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
> > ---
> > mm/page_alloc.c | 14 ++++----------
> > 1 file changed, 4 insertions(+), 10 deletions(-)
> >
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index 614cd0397ce3..e073cca4969e 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -3549,16 +3549,6 @@ should_reclaim_retry(gfp_t gfp_mask, unsigned order,
> > *no_progress_loops = 0;
> > else
> > (*no_progress_loops)++;
> > -
> > - /*
> > - * Make sure we converge to OOM if we cannot make any progress
> > - * several times in the row.
> > - */
> > - if (*no_progress_loops > MAX_RECLAIM_RETRIES) {
> > - /* Before OOM, exhaust highatomic_reserve */
> > - return unreserve_highatomic_pageblock(ac, true);
> > - }
> > -
> > /*
> > * Keep reclaiming pages while there is a chance this will lead
> > * somewhere. If none of the target zones can satisfy our allocation
> > @@ -3821,6 +3811,10 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
> > if (read_mems_allowed_retry(cpuset_mems_cookie))
> > goto retry_cpuset;
> >
> > + /* Before OOM, exhaust highatomic_reserve */
> > + if (unreserve_highatomic_pageblock(ac, true))
> > + goto retry;
> > +
>
> OK, this can help for higher order requests when we do not exhaust all
> the retries and fail on compaction but I fail to see how can this help
> for order-0 requets which was what happened in this case. I am not
> saying this is wrong, though.
The should_reclaim_retry can return false although no_progress_loop is less
than MAX_RECLAIM_RETRIES unless eligible zones has enough reclaimable pages
by the progress_loop. In that case, unreserve_highatomic_pageblock cannot
be called so that VM can keep a pageblock(e.g., 2M) for highatomic reserve.
Then, zone_watermark_ok subtracts nr_reserved_highatomic pages for the
pass/fail decision whichs is very conservative but no choice for the hot
path performance. With that, order-0 allocation can be failed.
Thanks.
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