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Subject: Re: [PATCH] remove throttle_vm_writeout()
From: Trond Myklebust <trond.myklebust@fys.uio.no>
To: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Miklos Szeredi <miklos@szeredi.hu>, akpm@linux-foundation.org,
       wfg@mail.ustc.edu.cn, linux-mm@kvack.org, linux-kernel@vger.kernel.org
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Date: Fri, 05 Oct 2007 15:20:43 -0400
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On Fri, 2007-10-05 at 20:32 +0200, Peter Zijlstra wrote:
> Well, the thing is, we throttle pageout in throttle_vm_writeout(). As it
> stand we can deadlock there because it just waits for the numbers to
> drop, and unstable pages don't automagically dissapear. Only
> write_inodes() - normally called from balance_dirty_pages() will call
> COMMIT.
> 
> So my thought was that calling pageout() on an unstable page would do
> the COMMIT - we're low on memory, otherwise we would not be paging, so
> getting rid of unstable pages seems to make sense to me.

Why not rather track which mappings have large numbers of outstanding
unstable writes at the VM level, and then add some form of callback to
allow it to notify the filesystem when it needs to flush them out?

Cheers
  Trond