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From: Christoph Hellwig <hch@infradead.org>
To: Michal Hocko <mhocko@kernel.org>
Cc: "Darrick J. Wong" <darrick.wong@oracle.com>,
	linux-mm@kvack.org, linux-fsdevel@vger.kernel.org,
	LKML <linux-kernel@vger.kernel.org>,
	Dave Chinner <david@fromorbit.com>
Subject: Re: implicit AOP_FLAG_NOFS for grab_cache_page_write_begin
Date: Fri, 17 Apr 2020 00:29:31 -0700	[thread overview]
Message-ID: <20200417072931.GA20822@infradead.org> (raw)
In-Reply-To: <20200415070228.GW4629@dhcp22.suse.cz>

On Wed, Apr 15, 2020 at 09:02:28AM +0200, Michal Hocko wrote:
> Hi,
> I have just received a bug report about memcg OOM [1]. The underlying
> issue is memcg specific but the stack trace made me look at the write(2)
> patch and I have noticed that iomap_write_begin enforces AOP_FLAG_NOFS
> which means that all the page cache that has to be allocated is
> GFP_NOFS. What is the reason for this? Do all filesystems really need
> the reclaim protection? I was hoping that those filesystems which really
> need NOFS context would be using the scope API
> (memalloc_nofs_{save,restore}.

This comes from the historic XFS code, and this commit from Dave
in particular:

commit aea1b9532143218f8599ecedbbd6bfbf812385e1
Author: Dave Chinner <dchinner@redhat.com>
Date:   Tue Jul 20 17:54:12 2010 +1000

    xfs: use GFP_NOFS for page cache allocation

    Avoid a lockdep warning by preventing page cache allocation from
    recursing back into the filesystem during memory reclaim.



  reply	other threads:[~2020-04-17  7:29 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-04-15  7:02 implicit AOP_FLAG_NOFS for grab_cache_page_write_begin Michal Hocko
2020-04-17  7:29 ` Christoph Hellwig [this message]
2020-04-17  8:00   ` Michal Hocko
2020-04-17  8:06     ` Christoph Hellwig

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