Re: [RFC 2/3] mm: throttle on IO only when there are too many dirty and writeback pages

From: Michal Hocko <mhocko@kernel.org>
To: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: linux-mm@kvack.org, "'Andrew Morton'" <akpm@linux-foundation.org>,
	"'Linus Torvalds'" <torvalds@linux-foundation.org>,
	"'Mel Gorman'" <mgorman@suse.de>,
	"'Johannes Weiner'" <hannes@cmpxchg.org>,
	"'Rik van Riel'" <riel@redhat.com>,
	"'David Rientjes'" <rientjes@google.com>,
	"'Tetsuo Handa'" <penguin-kernel@I-love.SAKURA.ne.jp>,
	"'LKML'" <linux-kernel@vger.kernel.org>,
	Christoph Lameter <cl@linux.com>
Subject: Re: [RFC 2/3] mm: throttle on IO only when there are too many dirty and writeback pages
Date: Fri, 30 Oct 2015 09:37:09 +0100	[thread overview]
Message-ID: <20151030083709.GD18429@dhcp22.suse.cz> (raw)
In-Reply-To: <00f301d112ca$14db86c0$3e929440$@alibaba-inc.com>

On Fri 30-10-15 12:18:50, Hillf Danton wrote:
> 
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -3191,8 +3191,23 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
> >  		 */
> >  		if (__zone_watermark_ok(zone, order, min_wmark_pages(zone),
> >  				ac->high_zoneidx, alloc_flags, target)) {
> > -			/* Wait for some write requests to complete then retry */
> > -			wait_iff_congested(zone, BLK_RW_ASYNC, HZ/50);
> > +			unsigned long writeback = zone_page_state(zone, NR_WRITEBACK),
> > +				      dirty = zone_page_state(zone, NR_FILE_DIRTY);
> > +
> > +			if (did_some_progress)
> > +				goto retry;
> > +
> > +			/*
> > +			 * If we didn't make any progress and have a lot of
> > +			 * dirty + writeback pages then we should wait for
> > +			 * an IO to complete to slow down the reclaim and
> > +			 * prevent from pre mature OOM
> > +			 */
> > +			if (2*(writeback + dirty) > reclaimable)
> > +				congestion_wait(BLK_RW_ASYNC, HZ/10);
> > +			else
> > +				cond_resched();
> > +
> 
> Looks the vmstat updater issue is not addressed.

This is not the aim of this patch set.
-- 
Michal Hocko
SUSE Labs