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

[Andrew Morton <akpm@linux-foundation.org>]

On Sun, 25 Mar 2007 23:10:21 +0200
Miklos Szeredi <miklos@szeredi.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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