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

KAMEZAWA Hiroyuki
2012-02-16T02:05:35Z

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

> There should be no logic changes in this patchset, this is only tossing bits around.
> [ This patchset is on top some memcg cleanup/rework patches,
> which I sent to linux-mm@ today/yesterday ]
>
> Most of things in this patchset are self-descriptive, so here brief plan:
>

AFAIK, Hugh Dickins said he has per-zone-per-lru-lock and is testing it.
So, please CC him and Johannes, at least.

> * Transmute struct lruvec into struct book. Like real book this struct will
> store set of pages for one zone. It will be working unit for reclaimer code.
> [ If memcg is disabled in config there will only one book embedded into struct zone ]
>

Why you need to add new structure rahter than enhancing lruvec ?
"book" means a binder of pages ?

> * move page-lru counters to struct book
> [ this adds extra overhead in add_page_to_lru_list()/del_page_from_lru_list() for
> non-memcg case, but I believe it will be invisible, only one non-atomic add/sub
> in the same cacheline with lru list ]
>

This seems straightforward.

> * unify inactive_list_is_low_global() and cleanup reclaimer code
> * replace struct mem_cgroup_zone with single pointer to struct book

Hm, ok.

> * 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 ?

Thanks,
-Kame