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 15:17:16 -0400
From:	Christoph Hellwig <hch@...radead.org>
To:	Rik van Riel <riel@...hat.com>
Cc:	Christoph Hellwig <hch@...radead.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Mel Gorman <mel@....ul.ie>, 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>
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 03:13:09PM -0400, Rik van Riel wrote:
> Why?   How about because you know the stack is not big enough
> to have the XFS call path on it twice? :)
> 
> Isn't the whole purpose of this patch series to prevent writepage
> from being called by the VM, when invoked from a deep callstack
> like xfs writepage?

It's not invoked from xfs writepage, but from xfs_file_aio_write via
generic_file_buffered_write.  Which isn't actually an all that deep
callstack, just en example of one that's alread bad enough to overflow
the stack.

> That sounds a lot like simply wanting to not have GFP_FS...

There's no point in sprinkling random GFP_NOFS flags.  It's not just
the filesystem code that uses a lot of stack.

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