From: David Howells <dhowells@redhat.com>
To: Andrew Morton <akpm@osdl.org>
Cc: David Howells <dhowells@redhat.com>,
torvalds@osdl.org, steved@redhat.com, trond.myklebust@fys.uio.no,
aviro@redhat.com, linux-fsdevel@vger.kernel.org,
linux-cachefs@redhat.com, nfsv4@linux-nfs.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 13/14] FS-Cache: Release page->private in failed readahead [try #8]
Date: Fri, 12 May 2006 17:23:18 +0100 [thread overview]
Message-ID: <1976.1147450998@warthog.cambridge.redhat.com> (raw)
In-Reply-To: <20060512071100.5c5d52e9.akpm@osdl.org>
Andrew Morton <akpm@osdl.org> wrote:
> > SetPageLocked(page);
>
> if (TestSetPagLocked(page))
> BUG();
>
> would make me more comfortable..
That shouldn't be necessary if add_to_page_cache() also doesn't do that, but
if you wish, I can do that - it's the error handling path, so it doesn't
matter too much performancewise.
> > > For the second hunk, is it not possible to do this cleanup in the callback
> > > function?
> >
> > Which callback function?
>
> I was referring to the filler_t thingy. Is it not possible to get control
> of that?
Well, the filler_t thing is generally a_ops->readpage from the caller fs, but
we don't want to call that if add_to_page_cache() failed, and we don't want to
call it if we're just discarding a bunch of pages we've now no intention of
actually reading.
I suppose we could add another callback for ditching pages we don't want to
keep. This has the potential to be called quite a lot because of the way
readahead works on Linux.
> So please, can we have some comments in there which describe the new
> behaviour in a manner sufficient for a maintainer to follow so people don't
> break your stuff?
Okay... I'll add more comments. I should probably also extend the
documentation on releasepage(). It won't be till Monday though.
> > Out of interest, why do we need PG_private to say there's something in
> > page->private? Can't it just be assumed either that if page->private is
> > non-zero or that if a_ops->releasepage() is non-NULL, then we need to
> > "release" the page?
>
> page->private is an unsigned long, not a pointer. The core kernel hence
> cannot determine from its value whether or not it is live. For example, the
> fs might choose to treat it as a bitmap of which-blocks-are-uptodate and
> which-blocks-are-dirty.
Then the second option is still possible (calling releasepage()
unconditionally).
David
next prev parent reply other threads:[~2006-05-12 16:23 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-05-10 16:01 [PATCH 00/14] Permit filesystem local caching and NFS superblock sharing [try #8] David Howells
2006-05-10 16:01 ` [PATCH 01/14] NFS: Permit filesystem to override root dentry on mount " David Howells
2006-05-10 16:01 ` [PATCH 02/14] NFS: Permit filesystem to perform statfs with a known root dentry " David Howells
2006-05-10 16:01 ` [PATCH 03/14] NFS: Abstract out namespace initialisation " David Howells
2006-05-10 16:01 ` [PATCH 04/14] NFS: Add dentry materialisation op " David Howells
2006-05-10 16:01 ` [PATCH 07/14] FS-Cache: Provide a filesystem-specific sync'able page bit " David Howells
2006-05-10 16:01 ` [PATCH 08/14] FS-Cache: Add notification of page becoming writable to VMA ops " David Howells
2006-05-10 16:01 ` [PATCH 09/14] FS-Cache: Avoid ENFILE checking for kernel-specific open files " David Howells
2006-05-10 16:01 ` [PATCH 11/14] FS-Cache: Make kAFS use FS-Cache " David Howells
2006-05-10 16:01 ` [PATCH 13/14] FS-Cache: Release page->private in failed readahead " David Howells
2006-05-11 17:40 ` Andrew Morton
2006-05-12 12:34 ` David Howells
2006-05-12 14:11 ` Andrew Morton
2006-05-12 16:23 ` David Howells [this message]
2006-05-10 16:01 ` [PATCH 14/14] NFS: Use local caching " David Howells
[not found] ` <20060510160132.9058.35796.stgit@warthog.cambridge.redhat.com>
2006-05-10 16:23 ` [PATCH 06/14] NFS: Share NFS superblocks per-protocol per-server per-FSID " Christoph Hellwig
2006-05-10 16:44 ` David Howells
2006-05-12 10:51 ` [PATCH 02/14] NFS: Permit filesystem to perform statfs with a known root dentry [try #9] David Howells
2006-05-15 5:46 ` Nathan Scott
2006-05-12 12:49 ` [PATCH 13/14] FS-Cache: Release page->private in failed readahead " David Howells
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