linux-kernel - Re: [RFC 01/13] mm, compaction: don't isolate PageWriteback pages in MIGRATE_SYNC

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Date:	Wed, 11 May 2016 14:40:40 +0200
From:	Michal Hocko <mhocko@...nel.org>
To:	Vlastimil Babka <vbabka@...e.cz>
Cc:	linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Rik van Riel <riel@...hat.com>,
	David Rientjes <rientjes@...gle.com>,
	Mel Gorman <mgorman@...hsingularity.net>,
	Johannes Weiner <hannes@...xchg.org>,
	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Hugh Dickins <hughd@...gle.com>
Subject: Re: [RFC 01/13] mm, compaction: don't isolate PageWriteback pages in
 MIGRATE_SYNC_LIGHT mode

On Tue 10-05-16 09:35:51, Vlastimil Babka wrote:
> From: Hugh Dickins <hughd@...gle.com>
> 
> At present MIGRATE_SYNC_LIGHT is allowing __isolate_lru_page() to
> isolate a PageWriteback page, which __unmap_and_move() then rejects
> with -EBUSY: of course the writeback might complete in between, but
> that's not what we usually expect, so probably better not to isolate it.

this makes a lot of sense regardless the rest of the series. I will have
a look at the rest tomorrow more closely.

> 
> Signed-off-by: Hugh Dickins <hughd@...gle.com>
> Signed-off-by: Vlastimil Babka <vbabka@...e.cz>

Acked-by: Michal Hocko <mhocko@...e.com>

> ---
>  mm/compaction.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/compaction.c b/mm/compaction.c
> index c72987603343..481004c73c90 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -1146,7 +1146,7 @@ static isolate_migrate_t isolate_migratepages(struct zone *zone,
>  	struct page *page;
>  	const isolate_mode_t isolate_mode =
>  		(sysctl_compact_unevictable_allowed ? ISOLATE_UNEVICTABLE : 0) |
> -		(cc->mode == MIGRATE_ASYNC ? ISOLATE_ASYNC_MIGRATE : 0);
> +		(cc->mode != MIGRATE_SYNC ? ISOLATE_ASYNC_MIGRATE : 0);
>  
>  	/*
>  	 * Start at where we last stopped, or beginning of the zone as
> -- 
> 2.8.2

-- 
Michal Hocko
SUSE Labs