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From: Tejun Heo <tj@kernel.org>
To: Michal Hocko <mhocko@kernel.org>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>,
	viro@zeniv.linux.org.uk, linux-mm@kvack.org,
	linux-fsdevel@vger.kernel.org, Jan Kara <jack@suse.com>
Subject: Re: [PATCH] mm,writeback: Don't use memory reserves for wb_start_writeback
Date: Wed, 16 Mar 2016 13:46:17 -0700	[thread overview]
Message-ID: <20160316204617.GH21104@mtj.duckdns.org> (raw)
In-Reply-To: <20160314160900.GC11400@dhcp22.suse.cz>

Hello,

(cc'ing Jan)

On Mon, Mar 14, 2016 at 05:09:00PM +0100, Michal Hocko wrote:
> On Sun 13-03-16 23:22:23, Tetsuo Handa wrote:
> [...]
> 
> I am not familiar with the writeback code so I might be missing
> something essential here but why are we even queueing more and more
> work without checking there has been enough already scheduled or in
> progress.
>
> Something as simple as:
> diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
> index 6915c950e6e8..aa52e23ac280 100644
> --- a/fs/fs-writeback.c
> +++ b/fs/fs-writeback.c
> @@ -887,7 +887,7 @@ void wb_start_writeback(struct bdi_writeback *wb, long nr_pages,
>  {
>  	struct wb_writeback_work *work;
>  
> -	if (!wb_has_dirty_io(wb))
> +	if (!wb_has_dirty_io(wb) || writeback_in_progress(wb))
>  		return;

I'm not sure this would be safe.  It shouldn't harm correctness as
wb_start_writeback() isn't used in sync case but this might change
flush behavior in various ways.  Dropping GFP_ATOMIC as suggested by
Tetsuo is likely better.

Thanks.

-- 
tejun

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  reply	other threads:[~2016-03-16 20:46 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-03-13  5:32 [PATCH] mm,writeback: Don't use ALLOC_NO_WATERMARKS for wb_start_writeback Tetsuo Handa
2016-03-13 14:22 ` [PATCH] mm,writeback: Don't use memory reserves " Tetsuo Handa
2016-03-14 16:09   ` Michal Hocko
2016-03-16 20:46     ` Tejun Heo [this message]
2016-03-18 13:11       ` Jan Kara
2016-03-18 13:34         ` Michal Hocko
2016-03-18 13:42   ` Michal Hocko

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