linux-kernel - Re: [PATCH 2/2] fuse: wait for writeback in fuse_file

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Message-ID: <CAJfpeguOTuZQFVpKQ5aDVxEPDrmzt_bKwXpiNrXv5yVegoA0QA@mail.gmail.com>
Date:	Wed, 11 Sep 2013 12:12:31 +0200
From:	Miklos Szeredi <miklos@...redi.hu>
To:	Maxim Patlasov <mpatlasov@...allels.com>
Cc:	fuse-devel <fuse-devel@...ts.sourceforge.net>,
	Brian Foster <bfoster@...hat.com>,
	Pavel Emelianov <xemul@...allels.com>,
	Kernel Mailing List <linux-kernel@...r.kernel.org>,
	devel@...nvz.org
Subject: Re: [PATCH 2/2] fuse: wait for writeback in fuse_file_fallocate() -v2

On Fri, Aug 30, 2013 at 1:33 PM, Maxim Patlasov <mpatlasov@...allels.com> wrote:
> 08/30/2013 01:13 PM, Miklos Szeredi пишет:
>
>> On Thu, Aug 29, 2013 at 6:41 PM, Miklos Szeredi <miklos@...redi.hu> wrote:
>>>
>>> BTW, isn't it enough to do the filemap_write_and_wait() *plus* the
>>> fuse_set_nowrite()?
>>
>> Thought about it a bit and I think this should do fine.
>>
>> Any writes before the fallocate will go trough before the fallocate.
>> i_mutex guarantees that only one instance of fuse_set_nowrite() is
>> running.  Any mmaped writes during the fallocate() will go after the
>> fallocate request and the page cache truncation and that's fine too.
>> Page cache is consistent since it doens't contain pages for those
>> writes to the hole.  Subsequent reads to that area will fill them in.
>>
>> Any other concerns?
>
>
> No. What you suggest looks as a neat and correct solution. I'll resend the
> updated patch after some testing (since now till Monday).
>
> As for proof-of-correctness, all you wrote above is correct, but the first
> point had been boiling my mind for a while. I came to the following
> reasoning (hopefully it is what you meant):
>
> The fact that filemap_write_and_wait() returned infers that
> end_page_writeback() was called for all relevant pages. And fuse doesn't
> call it before adding request to fi->queued_writes and calling
> fuse_flush_writepages(). And the latter, in turn, guarantees proper
> accounting of request in fi->writectr. Here, of course, it's crucial that we
> can't have concurrent fuse_set_nowrite(), as you explained. Hence, so far as
> fi->writectr was bumped, fuse_set_nowrite() we call after
> filemap_write_and_wait() would wait until all changes have gone to the
> server.

Any news about this?

Thanks,
Miklos
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