linux-kernel - Re: [PATCH] mm,vmscan: Use accurate values for zone

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Date:	Fri, 23 Oct 2015 06:42:43 +0900
From:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:	htejun@...il.com, mhocko@...nel.org
Cc:	cl@...ux.com, linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	torvalds@...ux-foundation.org, rientjes@...gle.com,
	oleg@...hat.com, kwalker@...hat.com, akpm@...ux-foundation.org,
	hannes@...xchg.org, vdavydov@...allels.com, skozina@...hat.com,
	mgorman@...e.de, riel@...hat.com
Subject: Re: [PATCH] mm,vmscan: Use accurate values for zone_reclaimable()checks

Tejun Heo wrote:
> On Thu, Oct 22, 2015 at 05:49:22PM +0200, Michal Hocko wrote:
> > I am confused. What makes rescuer to not run? Nothing seems to be
> > hogging CPUs, we are just out of workers which are loopin in the
> > allocator but that is preemptible context.
> 
> It's concurrency management.  Workqueue thinks that the pool is making
> positive forward progress and doesn't schedule anything else for
> execution while that work item is burning cpu cycles.

Then, isn't below change easier to backport which will also alleviate
needlessly burning CPU cycles?

--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3385,6 +3385,7 @@ retry:
 	((gfp_mask & __GFP_REPEAT) && pages_reclaimed < (1 << order))) {
 		/* Wait for some write requests to complete then retry */
 		wait_iff_congested(ac->preferred_zone, BLK_RW_ASYNC, HZ/50);
+		schedule_timeout_uninterruptible(1);
 		goto retry;
 	}
 
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