linux-kernel - Re: [patch resend v4] update ctime and mtime for mmaped write

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Message-ID: <20070326211008.GS10459@waste.org>
Date:	Mon, 26 Mar 2007 16:10:09 -0500
From:	Matt Mackall <mpm@...enic.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Miklos Szeredi <miklos@...redi.hu>, a.p.zijlstra@...llo.nl,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [patch resend v4] update ctime and mtime for mmaped write

On Mon, Mar 26, 2007 at 02:00:36PM -0700, Andrew Morton wrote:
> On Sun, 25 Mar 2007 23:10:21 +0200
> Miklos Szeredi <miklos@...redi.hu> wrote:
> 
> > This patch makes writing to shared memory mappings update st_ctime and
> > st_mtime as defined by SUSv3:
> 
> Boy this is complicated.
> 
> Is there a simpler way of doing all this?  Say, we define a new page flag
> PG_dirtiedbywrite and we do SetPageDirtiedByWrite() inside write() and
> ClearPageDirtiedByWrite() whenever we propagate pte-dirtiness into
> page-dirtiness.  Then, when performing writeback we look to see if any of
> the dirty pages are !PageDirtiedByWrite() and, if so, we update [mc]time to
> current-time.
> 
> Or something like that - I'm just thinking out loud and picking holes in
> the above doesn't shut me up ;) We're adding complexity and some overhead
> and we're losing our recent msync() simplifications and this all hurts.  Is
> there some other way?  I think burning a page flag to avoid this additional
> complexity would be worthwhile.  

Aren't we basically out of those?

-- 
Mathematics is the supreme nostalgia of our time.
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