linux-kernel - Re: [RFC PATCH 0/6] Do not call ->writepage[s] from direct reclaim and use a

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Date:	Tue, 15 Jun 2010 12:45:07 -0400
From:	Christoph Hellwig <hch@...radead.org>
To:	Andrea Arcangeli <aarcange@...hat.com>
Cc:	Mel Gorman <mel@....ul.ie>, Christoph Hellwig <hch@...radead.org>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-mm@...ck.org, Dave Chinner <david@...morbit.com>,
	Chris Mason <chris.mason@...cle.com>,
	Nick Piggin <npiggin@...e.de>, Rik van Riel <riel@...hat.com>
Subject: Re: [RFC PATCH 0/6] Do not call ->writepage[s] from direct reclaim
 and use a_ops->writepages() where possible

On Tue, Jun 15, 2010 at 06:14:19PM +0200, Andrea Arcangeli wrote:
> Again not what looks like from the stack trace. Also grepping for
> PF_MEMALLOC in fs/xfs shows nothing. In fact it's ext4_write_inode
> that skips the write if PF_MEMALLOC is set, not writepage apparently
> (only did a quick grep so I might be wrong). I suspect
> ext4_write_inode is the case I just mentioned about slab shrink, not
> ->writepage ;).
> 
> inodes are small, it's no big deal to keep an inode pinned and not
> slab-reclaimable because dirty, while skipping real writepage in
> memory pressure could really open a regression in oom false positives!
> One pagecache much bigger than one inode and there can be plenty more
> dirty pagecache than inodes.

Btw, those comments in ext3/ext4 don't make much sense.  The only
time iput_final ever calls into ->write_inode is when the filesystem
is beeing unmounted, which never happens with PF_MEMALLOC set.

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