linux-kernel - Re: [PATCH] zero_user_page uses in fs/buffer.c and fs/libfs.c

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Date:	Tue, 1 May 2007 19:27:16 -0700
From:	"Nate Diller" <nate.diller@...il.com>
To:	"Christoph Lameter" <clameter@....com>
Cc:	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Satyam Sharma" <satyam.sharma@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] zero_user_page uses in fs/buffer.c and fs/libfs.c

On 5/1/07, Nate Diller <nate.diller@...il.com> wrote:
> On 5/1/07, Christoph Lameter <clameter@....com> wrote:
> > On Tue, 1 May 2007, Andrew Morton wrote:
> >
> > > As Satyam said, this will sometimes cause us to map and unmap the page
> > > twice, and to run flush_dcache_page() twice.  In not-terribly-uncommon
> > > circumstances in very frequently called functions.
> > >
> > > Doesn't seem worth it to me.
> >
> > Ok but we have that code three times. Should I add a variant of
> > zero_user_page that zeroes everything but the section specified?
> >
> > zero_user_page_allbut() ?
>
> the function already exists, it's called simple_prepare_write(), and i
> thought there were patches to convert those callsites in -mm ...
> although it looks like i let a review comment on that slide by.  I
> need to redo a bunch of patches for re-submission anyway, so i guess
> i'll deal with that tomorrow.
>
> NATE
>

well, leave it to me to reply too quickly, sorry.  i think we should
leave simple_prepare_write() the way it is, since it's a library
function itself.  the other two callsites in your patch are buffers,
which may themselves be smaller than a page so you would need a
special function for just those two uses, there's no other way to
avoid making two calls to flush_dcache_page().  if it's tremendously
important to you to eliminate open coding of these, maybe make a
'static int buffer_prepare_write()' or some such in fs/buffer.c

NATE
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