linux-kernel - Re: [PATCH] VM: Fix the gfp_mask in invalidate_complete

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Date:	Fri, 6 Oct 2006 19:33:11 -0700
From:	Andrew Morton <akpm@...l.org>
To:	Steve Dickson <SteveD@...hat.com>
Cc:	Trond Myklebust <Trond.Myklebust@...app.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] VM: Fix the gfp_mask in invalidate_complete_page2

On Fri, 06 Oct 2006 19:09:29 -0400
Steve Dickson <SteveD@...hat.com> wrote:

> > 
> > It's not 100% clear what the gfp_t _means_ in the try_to_release_page()
> > context.  Callees will rarely want to allocate memory (true?).  So it
> > conveys two concepts: 
> > 
> > a) can sleep. (__GFP_WAIT).  That's fairly straightforward
> > 
> > b) can take fs locks (__GFP_FS).  This is less clear.  By passing down
> >    __GFP_FS we're telling the callee that it's OK to take i_mutex, even
> >    lock_page().  That sounds pretty unsafe in this context, particularly
> >    the latter, as we're already holding a page lock.
> > 
> > So perhaps the safer and more appropriate solution here is to pass in a
> > bare __GFP_WAIT.
> I agree... __GFP_WAIT does seem to be a bit more straightforward...
> either way is find.. as long as it cause NFS to flush its pages...

Except NFS looks at __GFP_FS, so __GFP_WAIT won't help.

Oh well.  Passing __GFP_FS in here sort-of implies that it's OK to run
lock_page(), but if a ->releasepage() impementation tries to lock the page
it's passed then it needs its head read.

I made it GFP_KERNEL.
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