linux-kernel - Re: [PATCH 0/3] implement readpages() for block device to optimize sequential read

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Message-Id: <20140821144412.2a97f2a7400590097f3926de@linux-foundation.org>
Date:	Thu, 21 Aug 2014 14:44:12 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Akinobu Mita <akinobu.mita@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>, Jens Axboe <axboe@...nel.dk>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Jeff Moyer <jmoyer@...hat.com>, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 0/3] implement readpages() for block device to optimize
 sequential read

On Sat, 16 Aug 2014 02:09:44 +0900 Akinobu Mita <akinobu.mita@...il.com> wrote:

> 2014-08-15 7:04 GMT+09:00 Andrew Morton <akpm@...ux-foundation.org>:
> > On Tue,  5 Aug 2014 23:38:31 +0900 Akinobu Mita <akinobu.mita@...il.com> wrote:
> >
> >> This patchset implements readpages() operation for block device by
> >> using mpage_readpages() which can create multipage BIOs instead of
> >> BIOs for each page and reduce system CPU time consumption.
> >
> > Patchset is simple and straightforward enough.  But who the
> > heck cares about the performance of buffered reads from /dev/XXX?
> 
> I tend to consider the block device as a baseline when I measure the
> performance of the storage device.  So I was a bit surprised when I saw
> the performance of buffered reads from filesystem is better than the one
> from block device.  That is the reason about this patch for me.

OK.  The lack of readpages for blockdevs has been an outstanding oddity
for a decade or longer - I think it's just that nobody was motivated to
do it because the workload isn't important.

But the implementation looks pretty simple so why not clean it up.

I grabbed the patches.
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