linux-kernel - Re: [PATCH RFC 00/15] mm: memory book keeping and lru

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Message-Id: <20120216110408.f35c3448.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Thu, 16 Feb 2012 11:04:08 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Konstantin Khlebnikov <khlebnikov@...nvz.org>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Hugh Dickins <hughd@...gle.com>,
	"hannes@...xchg.org" <hannes@...xchg.org>
Subject: Re: [PATCH RFC 00/15] mm: memory book keeping and lru_lock
 splitting

On Thu, 16 Feb 2012 02:57:04 +0400
Konstantin Khlebnikov <khlebnikov@...nvz.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

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