Date: Tue, 3 Jan 2012 12:26:07 +0200 From: Kostik Belousov <kostikbel@gmail.com> To: Don Lewis <truckman@freebsd.org> Cc: attilio@freebsd.org, flo@freebsd.org, current@freebsd.org, mckusick@mckusick.com, phk@phk.freebsd.dk, seanbru@yahoo-inc.com Subject: Re: dogfooding over in clusteradm land Message-ID: <20120103102607.GO50300@deviant.kiev.zoral.com.ua> In-Reply-To: <201201030945.q039jQ4j007027@gw.catspoiler.org> References: <20120103091819.GN50300@deviant.kiev.zoral.com.ua> <201201030945.q039jQ4j007027@gw.catspoiler.org>
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On Tue, Jan 03, 2012 at 01:45:26AM -0800, Don Lewis wrote:
> On 3 Jan, Kostik Belousov wrote:
>
> > This sounds very plausible. I think that there is no sense in restarting
> > the scan if it is requested in async mode at all. See below.
> >
> > Would be thrilled if this finally solves the svn2cvs issues.
> >
> > commit 41aaafe5e3be5387949f303b8766da64ee4a521f
> > Author: Kostik Belousov <kostik@sirion>
> > Date: Tue Jan 3 11:16:30 2012 +0200
> >
> > Do not restart the scan in vm_object_page_clean() if requested
> > mode is async.
> >
> > Proposed by: truckman
> >
> > diff --git a/sys/vm/vm_object.c b/sys/vm/vm_object.c
> > index 716916f..52fc08b 100644
> > --- a/sys/vm/vm_object.c
> > +++ b/sys/vm/vm_object.c
> > @@ -841,7 +841,8 @@ rescan:
> > if (p->valid == 0)
> > continue;
> > if (vm_page_sleep_if_busy(p, TRUE, "vpcwai")) {
> > - if (object->generation != curgeneration)
> > + if ((flags & OBJPC_SYNC) != 0 &&
> > + object->generation != curgeneration)
> > goto rescan;
> > np = vm_page_find_least(object, pi);
> > continue;
>
> I wonder if it would make more sense to just skip the busy pages in
> async mode instead of sleeping ...
>
It would be too much weakening the guarantee of the vfs_msync(MNT_NOWAIT)
to not write such pages, IMO. Busy state indeed means that the page most
likely undergoing the i/o, but in case it is not, we would not write it
at all.
Lets see whether the change alone helps. Do you agree ?
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