From: Michal Hocko <mhocko@kernel.org>
To: Yang Shi <yang.shi@linux.alibaba.com>
Cc: "Theodore Y. Ts'o" <tytso@mit.edu>,
mgorman@techsingularity.net, adilger.kernel@dilger.ca,
darrick.wong@oracle.com, dchinner@redhat.com,
akpm@linux-foundation.org, linux-ext4@vger.kernel.org,
linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/2] fs: ext4: use BUG_ON if writepage call comes from direct reclaim
Date: Wed, 4 Jul 2018 16:03:06 +0200 [thread overview]
Message-ID: <20180704140306.GB22669@dhcp22.suse.cz> (raw)
In-Reply-To: <6c305241-d502-b8ea-a187-54c33e4ca692@linux.alibaba.com>
On Tue 03-07-18 10:05:04, Yang Shi wrote:
>
>
> On 7/3/18 3:39 AM, Theodore Y. Ts'o wrote:
> > On Tue, Jul 03, 2018 at 12:11:18PM +0800, Yang Shi wrote:
> > > direct reclaim doesn't write out filesystem page, only kswapd could do
> > > it. So, if the call comes from direct reclaim, it is definitely a bug.
> > >
> > > And, Mel Gormane also mentioned "Ultimately, this will be a BUG_ON." In
> > > commit 94054fa3fca1fd78db02cb3d68d5627120f0a1d4 ("xfs: warn if direct
> > > reclaim tries to writeback pages").
> > >
> > > Although it is for xfs, ext4 has the similar behavior, so elevate
> > > WARN_ON to BUG_ON.
> > >
> > > And, correct the comment accordingly.
> > >
> > > Cc: Mel Gorman <mgorman@techsingularity.net>
> > > Cc: "Theodore Ts'o" <tytso@mit.edu>
> > > Cc: Andreas Dilger <adilger.kernel@dilger.ca>
> > > Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com>
> > What's the upside of crashing the kernel if the file sytsem can handle it?
>
> I'm not sure if it is a good choice to let filesystem handle such vital VM
> regression. IMHO, writing out filesystem page from direct reclaim context is
> a vital VM bug. It means something is definitely wrong in VM. It should
> never happen.
Could you be more specific about the vital part please? Issuing
writeback from the direct reclaim surely can be sub-optimal. But since
we have quite a large stacks it shouldn't overflow immediately even for
more complex storage setups. So what is the _vital_ bug here?
--
Michal Hocko
SUSE Labs
prev parent reply other threads:[~2018-07-04 14:03 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-07-03 4:11 [PATCH 1/2] fs: ext4: use BUG_ON if writepage call comes from direct reclaim Yang Shi
2018-07-03 4:11 ` [PATCH 2/2] fs: xfs: " Yang Shi
2018-07-03 4:37 ` Dave Chinner
2018-07-03 17:19 ` Darrick J. Wong
2018-07-03 10:39 ` [PATCH 1/2] fs: ext4: " Theodore Y. Ts'o
2018-07-03 17:05 ` Yang Shi
2018-07-03 23:10 ` Yang Shi
2018-07-03 23:43 ` Theodore Y. Ts'o
2018-07-04 14:03 ` Michal Hocko [this message]
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