To: Linus Torvalds <torvalds@linux-foundation.org>
CC: Trond.Myklebust@netapp.com, nbowler@elliptictech.com,
        linux-kernel@vger.kernel.org, linux-nfs@vger.kernel.org,
        akpm@linux-foundation.org, hughd@google.com, riel@redhat.com,
        hch@lst.de, viro@zeniv.linux.org.uk
In-reply-to: <AANLkTi=C8UtWwctEgBY2584d8fDV3OHpf+mGNnQO8ZJt@mail.gmail.com>
	(message from Linus Torvalds on Wed, 1 Dec 2010 08:17:38 -0800)
Subject: Re: [PATCH v2 3/3] NFS: Fix a memory leak in nfs_readdir
References: <1291217804-11257-1-git-send-email-Trond.Myklebust@netapp.com>
 <1291217804-11257-2-git-send-email-Trond.Myklebust@netapp.com>
 <20101201150428.GA2879@elliptictech.com> <1291217804-11257-3-git-send-email-Trond.Myklebust@netapp.com>
 <1291217804-11257-4-git-send-email-Trond.Myklebust@netapp.com> <AANLkTi=C8UtWwctEgBY2584d8fDV3OHpf+mGNnQO8ZJt@mail.gmail.com>
Message-Id: <E1PNrQc-0005zr-7B@pomaz-ex.szeredi.hu>
From: Miklos Szeredi <miklos@szeredi.hu>
Date: Wed, 01 Dec 2010 19:29:18 +0100
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 4077
Lines: 81

On Wed, 1 Dec 2010, Linus Torvalds wrote:
> --00032557542a0c5e6004965ba615
> Content-Type: text/plain; charset=ISO-8859-1
> 
> On Wed, Dec 1, 2010 at 7:36 AM, Trond Myklebust
> <Trond.Myklebust@netapp.com> wrote:
> >
> > We need to ensure that the entries in the nfs_cache_array get cleared
> > when the page is removed from the page cache. To do so, we use the
> > releasepage address_space operation (which also requires us to set
> > the Pg_private flag).
> 
> So I really think that the whole "releasepage" use in NFS is simply
> overly complicated and was obviously too subtle.
> 
> The whole need for odd return values, for the page lock, and for the
> addition of clearing the up-to-date bit comes from the fact that this
> wasn't really what releasepage was designed for.
> 
> 'releasepage' was really designed for the filesystem having its own
> version of 'try_to_free_buffers()', which is just an optimistic "ok,
> we may be releasing this page, so try to get rid of any IO structures
> you have cached". It wasn't really a memory management thing.
> 
> And the thing is, it looks trivial to do the memory management
> approach by adding a new callback that gets called after the page is
> actually removed from the page cache. If we do that, then there are no
> races with any other users, since we remove things from the page cache
> atomically wrt page cache lookup. So the need for playing games with
> page locking and 'uptodate' simply goes away. As does the PG_private
> thing or the interaction with invalidatepage() etc.
> 
> So this is a TOTALLY UNTESTED trivial patch that just adds another
> callback. Does this work? I dunno. But I get the feeling that instead
> of having NFS work around the odd semantics that don't actually match
> what NFS wants, introducing a new callback with much simpler semantics
> would be simpler for everybody, and avoid the need for subtle code.
> 
> Hmm?
> 
>                    Linus
> 
> --00032557542a0c5e6004965ba615
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> --00032557542a0c5e6004965ba615--

This violates the "Really. Don't send patches as attachments."
lkml-faq set forth by yourself ;)

Am I the only one who still uses a mail reader that doesn't decode
mime by default?  Maybe it's time to move on...

Thanks,
Miklos
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