[linux-cifs-client] Re: set last write time = fsync ?
Jeff Layton
jlayton at redhat.com
Fri Mar 14 23:19:08 GMT 2008
On Fri, 14 Mar 2008 16:38:27 -0500
"Steve French" <smfrench at gmail.com> wrote:
> On Fri, Mar 14, 2008 at 3:35 PM, Jeff Layton <jlayton at redhat.com> wrote:
> > On Fri, 14 Mar 2008 14:19:06 -0500
> >
> > "Steve French" <smfrench at gmail.com> wrote:
> >
> > > On Fri, Mar 14, 2008 at 11:55 AM, Jeff Layton <jlayton at redhat.com> wrote:
> > > > On Fri, 14 Mar 2008 11:16:41 -0500
> > > >
> > > > "Steve French" <smfrench at gmail.com> wrote:
> > > >
> > > >
> > > > > I don't worry about flushing atime (anyone crazy enough to do that
> > > > > would pay a huge performance penalty).
> > > > > Access is usually checked on open right ... so once a file is open
> > > > > even if the file becomes read-only, the writes, even cached writes
> > > > > continue.
> > > > >
> > > >
> > > > Ahh, you're correct. I've been doing a lot of NFS work lately and was
> > > > thinking stateless... :-)
> > > >
> > > > That patch should be OK then, though I think if someone is purposefully
> > > > setting the atime we should take care not to clobber it. We're not
> > > > going to be going through this codepath on every atime update, are we?
> > > > Just on utimes() type calls, correct? If so, doing a flush on atime
> > > > updates might be reasonable as well...
> > > >
> > > > Jeff Layton <jlayton at redhat.com>
> > > >
> > >
> > > I don't think we need to flush before setting (just) atime.
> > > If the problem with timestamps is delayed writes getting written out
> > > on close ... won't close update the atime anyway?
> > >
> > >
> > Consider that an app like tar might do something like this:
> >
> > open()
> > write()
> > write()
> > write()
> > close()
> > utimes()
> >
> > The app would likely set the mtime too, but I'm not sure we should make
> > that assumption. The question is -- should we allow that utimes() call
> > to be clobbered by writes lingering around after the close() returns?
>
> There can't be writes lingering around after the close ... filp_close does
> a flush before calling fput.
>
>
Right, but we don't do filemap_fdatawait() on flush so I suppose we're
not guaranteed to actually have all the writes out on the wire before
the close occurs.
IIRC, the current writepages implementation in cifs I think does
effectively wait until all the writes have completed before returning,
so a filemap_fdatawait wouldn't really do make any difference.
Anyway, after looking back over the original problem, I think I'm
convinced that your original patch is OK.
ACK
Thanks,
--
Jeff Layton <jlayton at redhat.com>
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