linux-kernel - Re: [PATCH v3 5/7] swap: Use bdev_read_page() / bdev_write

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Message-ID: <20140424185740.GE5886@linux.intel.com>
Date:	Thu, 24 Apr 2014 14:57:40 -0400
From:	Matthew Wilcox <willy@...ux.intel.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Matthew Wilcox <matthew.r.wilcox@...el.com>,
	linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Hugh Dickins <hughd@...gle.com>
Subject: Re: [PATCH v3 5/7] swap: Use bdev_read_page() / bdev_write_page()

On Thu, Apr 24, 2014 at 11:18:17AM -0700, Andrew Morton wrote:
> On Sun, 13 Apr 2014 18:59:54 -0400 Matthew Wilcox <matthew.r.wilcox@...el.com> wrote:
> 
> >  mm/page_io.c | 23 +++++++++++++++++++++--
> >  1 file changed, 21 insertions(+), 2 deletions(-)
> 
> Some changelog here would be nice.  What were the reasons for the
> change?  Any observable performance changes?

Whoops ... I could swear I wrote one.  Wonder what happened to it.  Here
was all I had:

We can avoid allocating a BIO if we use the writepage path instead of
the Direct I/O path.

But that's kind of lame.  I don't have any performance numbers right now,
so how about we go with:

By calling the device driver to write the page directly, we avoid
allocating a BIO, which allows us to free memory without allocating
memory.
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