Re: [PATCH RFC 00/15] mm: memory book keeping and lru_lock splitting

KAMEZAWA Hiroyuki
2012-02-16T08:25:34Z

On Thu, 16 Feb 2012 09:43:52 +0400
Konstantin Khlebnikov <khlebnikov@openvz.org> wrote:

> KAMEZAWA Hiroyuki wrote:
> > On Thu, 16 Feb 2012 02:57:04 +0400
> > Konstantin Khlebnikov<khlebnikov@openvz.org> wrote:

> >> * optimize page to book translations, move it upper in the call stack,
> >> replace some struct zone arguments with struct book pointer.
> >>
> >
> > a page->book transrater from patch 2/15
> >
> > +struct book *page_book(struct page *page)
> > +{
> > + struct mem_cgroup_per_zone *mz;
> > + struct page_cgroup *pc;
> > +
> > + if (mem_cgroup_disabled())
> > + return&page_zone(page)->book;
> > +
> > + pc = lookup_page_cgroup(page);
> > + if (!PageCgroupUsed(pc))
> > + return&page_zone(page)->book;
> > + /* Ensure pc->mem_cgroup is visible after reading PCG_USED. */
> > + smp_rmb();
> > + mz = mem_cgroup_zoneinfo(pc->mem_cgroup,
> > + page_to_nid(page), page_zonenum(page));
> > + return&mz->book;
> > +}
> >
> > What happens when pc->mem_cgroup is rewritten by move_account() ?
> > Where is the guard for lockless access of this ?
>
> Initially this suppose to be protected with lru_lock, in final patch they are protected with rcu.

Hmm, VM_BUG_ON(!PageLRU(page)) ?

move_account() overwrites pc->mem_cgroup with isolating page from LRU.
but it doesn't take lru_lock.

BTW, what amount of perfomance benefit ?

Thanks,
-Kame