On Fri, 6 Sep 2013 15:00:56 +0000 "Myklebust, Trond" <Trond.Myklebust@xxxxxxxxxx> wrote: > On Fri, 2013-09-06 at 09:36 -0400, Jeff Layton wrote: > > On Thu, 5 Sep 2013 17:34:20 -0500 > > Quentin Barnes <qbarnes@xxxxxxxxx> wrote: > > > > > On Thu, Sep 05, 2013 at 09:57:24PM +0000, Myklebust, Trond wrote: > > > > On Thu, 2013-09-05 at 16:36 -0500, Quentin Barnes wrote: > > > > > On Thu, Sep 05, 2013 at 08:02:01PM +0000, Myklebust, Trond wrote: > > > > > > On Thu, 2013-09-05 at 14:11 -0500, Quentin Barnes wrote: > > > > > > > On Thu, Sep 05, 2013 at 12:03:03PM -0500, Malahal Naineni wrote: > > > > > > > > Neil Brown posted a patch couple days ago for this! > > > > > > > > > > > > > > > > http://thread.gmane.org/gmane.linux.nfs/58473 > > > > > > > > > > > > > > I tried Neil's patch on a v3.11 kernel. The rebuilt kernel still > > > > > > > exhibited the same 1000s of WRITEs/sec problem. > > > > > > > > > > > > > > Any other ideas? > > > > > > > > > > > > Yes. Please try the attached patch. > > > > > > > > > > Great! That did the trick! > > > > > > > > > > Do you feel this patch could be worthy of pushing it upstream in its > > > > > current state or was it just to verify a theory? > > > > > > > > > > > > > > > In comparing the nfs_flush_incompatible() implementations between > > > > > RHEL5 and v3.11 (without your patch), the guts of the algorithm seem > > > > > more or less logically equivalent to me on whether or not to flush > > > > > the page. Also, when and where nfs_flush_incompatible() is invoked > > > > > seems the same. Would you provide a very brief pointer to clue me > > > > > in as to why this problem didn't also manifest circa 2.6.18 days? > > > > > > > > There was no nfs_vm_page_mkwrite() to handle page faults in the 2.6.18 > > > > days, and so the risk was that your mmapped writes could end up being > > > > sent with the wrong credentials. > > > > > > Ah! You're right that nfs_vm_page_mkwrite() was missing from > > > the original 2.6.18, so that makes sense, however, Red Hat had > > > backported that function starting with their RHEL5.9(*) kernels, > > > yet the problem doesn't manifest on RHEL5.9. Maybe the answer lies > > > somewhere in RHEL5.9's do_wp_page(), or up that call path, but > > > glancing through it, it all looks pretty close though. > > > > > > > > > (*) That was the source I using when comparing with the 3.11 source > > > when studying your patch since it was the last kernel known to me > > > without the problem. > > > > > > > I'm pretty sure RHEL5 has a similar problem, but it's unclear to me why > > you're not seeing it there. I have a RHBZ open vs. RHEL5 but it's marked > > private at the moment (I'll see about opening it up). I brought this up > > upstream about a year ago with this strawman patch: > > > > http://article.gmane.org/gmane.linux.nfs/51240 > > > > ...at the time Trond said he was working on a set of patches to track > > the open/lock stateid on a per-req basis. Did that approach not pan > > out? > > We've achieved what we wanted to do (Neil's lock recovery patch) without > that machinery, so for now, we're dropping that. > > > Also, do you need to do a similar fix to nfs_can_coalesce_requests? > > Yes. Good point! > Cool. FWIW, here's the original bug that was opened against RHEL5: https://bugzilla.redhat.com/show_bug.cgi?id=736578 ...the reproducer that Max cooked up is not doing mmapped I/O so there may be a difference there, but I haven't looked closely at why that is. -- Jeff Layton <jlayton@xxxxxxxxxx> -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
