linux-kernel - Re: [patch]mm: add more blk plug

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Date:	Mon, 26 Sep 2011 05:45:54 -0400
From:	Christoph Hellwig <hch@...radead.org>
To:	Shaohua Li <shaohua.li@...el.com>
Cc:	Christoph Hellwig <hch@...radead.org>,
	Jens Axboe <axboe@...nel.dk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: [patch]mm: add more blk plug

On Mon, Sep 26, 2011 at 03:38:47PM +0800, Shaohua Li wrote:
> On Mon, 2011-09-26 at 15:30 +0800, Christoph Hellwig wrote:
> > On Mon, Sep 26, 2011 at 10:30:26AM +0800, Shaohua Li wrote:
> > > Some filesystems implement .writepages. We don't have blk plug
> > > in such filesystems for .writepages.
> > 
> > Please add the plugging in the actual ->writepages instances.
> there are several filesystems have ->writepages. Can you share an hint
> why we don't add plugging in the do_writepages?

Because do_writepages is completely generic code with no knowledge of
block I/O.  I really don't want to have block plugging be intimately
tied into core VM/writeback code all over.  We've been there with
->sync_page, and it was a major pain - nevermind the additional (small)
overhead for the not block based filesystems.

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