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

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Date:	Fri, 06 Oct 2006 19:09:29 -0400
From:	Steve Dickson <SteveD@...hat.com>
To:	Andrew Morton <akpm@...l.org>
CC:	Trond Myklebust <Trond.Myklebust@...app.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] VM: Fix the gfp_mask in invalidate_complete_page2

Andrew Morton wrote:
> On Fri, 06 Oct 2006 18:19:27 -0400
> Trond Myklebust <Trond.Myklebust@...app.com> wrote:
> 
> 
>>On Fri, 2006-10-06 at 18:16 -0400, Trond Myklebust wrote:
>>
>>>Yeah using mapping_gfp_mask(mapping) sounds like a better option.
>>
>>Revised patch is attached...
> 
> 
> Well, it wasn't attached, but I can simulate it.
> 
> invalidate_complete_page() wants to be called from inside spinlocks by
> drop_pagecache(), so if we wanted to pull the same trick there we'd need to
> pass a new flag into invalidate_inode_pages().
That seems abit broken (wrt performance) that drop_pagecache_sb() holds
the fairly popular inode_lock while it invalidate pages...
Nobody else seem to...

> 
> 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...

steved.

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