Re: [PATCH v3 00/11] mm: fixup changers of per cpu pageset's ->highand ->batch

[Cody P Schafer]

On 04/10/2013 02:25 PM, Cody P Schafer wrote:
> On 04/10/2013 02:23 PM, Andrew Morton wrote:
> > On Wed, 10 Apr 2013 11:23:28 -0700 Cody P Schafer
> > <cody@xxxxxxxxxxxxxxxxxx> wrote:
> >
> > > "Problems" with the current code:
> > >   1. there is a lack of synchronization in setting ->high and ->batch in
> > >      percpu_pagelist_fraction_sysctl_handler()
> > >   2. stop_machine() in zone_pcp_update() is unnecissary.
> > >   3. zone_pcp_update() does not consider the case where
> > > percpu_pagelist_fraction is non-zero
> > >
> > > To fix:
> > >   1. add memory barriers, a safe ->batch value, an update side mutex
> > > when
> > >      updating ->high and ->batch, and use ACCESS_ONCE() for ->batch
> > > users that
> > >      expect a stable value.
> > >   2. avoid draining pages in zone_pcp_update(), rely upon the memory
> > > barriers added to fix #1
> > >   3. factor out quite a few functions, and then call the appropriate
> > > one.
> > >
> > > Note that it results in a change to the behavior of
> > > zone_pcp_update(), which is
> > > used by memory_hotplug. I'm rather certain that I've diserned (and
> > > preserved)
> > > the essential behavior (changing ->high and ->batch), and only
> > > eliminated
> > > unneeded actions (draining the per cpu pages), but this may not be
> > > the case.
> > >
> > > Further note that the draining of pages that previously took place in
> > > zone_pcp_update() occured after repeated draining when attempting to
> > > offline a
> > > page, and after the offline has "succeeded". It appears that the
> > > draining was
> > > added to zone_pcp_update() to avoid refactoring setup_pageset() into 2
> > > funtions.
> >
> > There hasn't been a ton of review activity for this patchset :(
> >
> > I'm inclined to duck it until after 3.9.  Do the patches fix any
> > noticeably bad userspace behavior?
>
> No, all the bugs are theoretical. Waiting should be fine.

Andrew, do you want me to resend this patch set in the hope of obtaining 
more review? If so, when?

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