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

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Message-Id: <20070326140036.f3352f81.akpm@linux-foundation.org>
Date:	Mon, 26 Mar 2007 14:00:36 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Miklos Szeredi <miklos@...redi.hu>
Cc:	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 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.  
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