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Re: [PATCH 0/2] Improve writeout pattern from xfs_flush_pages()

To: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Subject: Re: [PATCH 0/2] Improve writeout pattern from xfs_flush_pages()
From: Jan Kara <jack@xxxxxxx>
Date: Thu, 4 Aug 2011 14:37:22 +0200
Cc: Jan Kara <jack@xxxxxxx>, xfs@xxxxxxxxxxx, linux-fsdevel@xxxxxxxxxxxxxxx
In-reply-to: <20110804121916.GA17783@xxxxxxxxxxxxx>
References: <1312404545-15400-1-git-send-email-jack@xxxxxxx> <20110803214206.GA20477@xxxxxxxxxxxxx> <20110804103616.GF17196@xxxxxxxxxxxxx> <20110804104210.GA30823@xxxxxxxxxxxxx> <20110804120724.GA20800@xxxxxxxxxxxxx> <20110804121916.GA17783@xxxxxxxxxxxxx>
User-agent: Mutt/1.5.20 (2009-06-14)
On Thu 04-08-11 08:19:16, Christoph Hellwig wrote:
> On Thu, Aug 04, 2011 at 02:07:24PM +0200, Jan Kara wrote:
> >   Hmm, BTW, shouldn't the call to xfs_flush_pages() in
> > xfs_file_buffered_aio_write() be converted to an asynchronous one? I don't
> > quite see a point in waiting for io completion... Generally, flushing of
> > the inode there seems of limited usefulness to me since that inode could be
> > just a tiny victim not holding much delayallocated blocks.
> 
> This comes from commit
> 
>       xfs: make inode flush at ENOSPC synchronous
> 
> from Dave - before that it was asynchronous and in weird context, so
> it seems we defintively need it to be synchronous.
  From the changelog it seems it needs to be synchronous in the sense that
we don't offload flushing to a different thread as we used to. Also the
reason why previously flushing didn't work was that we held page locks and
IO lock but it's not the case in xfs_file_buffered_aio_write() anymore. So
filemap_flush() still looks like an appropriate thing to me.

> I agree that just flushing this inode seems like a rather odd handling
> for ENOSPC.  It's even more odd as we already use the big hammer before
> in when we git ENOSPC in ->write_begin.  The only thing I can imagine is
> that this is the last attempt to get anything freed.
  OK, I'll leave it there then. I just wonder whether I should convert it
to filemap_flush() or to filemap_write_and_wait()...

                                                                Honza
-- 
Jan Kara <jack@xxxxxxx>
SUSE Labs, CR

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