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From: Michal Hocko <mhocko@kernel.org>
To: Christoph Hellwig <hch@infradead.org>,
	"Darrick J. Wong" <darrick.wong@oracle.com>
Cc: linux-mm@kvack.org, linux-fsdevel@vger.kernel.org,
	LKML <linux-kernel@vger.kernel.org>
Subject: implicit AOP_FLAG_NOFS for grab_cache_page_write_begin
Date: Wed, 15 Apr 2020 09:02:28 +0200	[thread overview]
Message-ID: <20200415070228.GW4629@dhcp22.suse.cz> (raw)

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}.

Could you clarify please?

[1] http://lkml.kernel.org/r/20200414212558.58eaab4de2ecf864eaa87e5d@linux-foundation.org
-- 
Michal Hocko
SUSE Labs


             reply	other threads:[~2020-04-15  7:02 UTC|newest]

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

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