Re: [RFC] [PATCH 3/7 v2] memcg: remove PCG_MOVE_LOCK flag from pc->flags

["Kirill A. Shutemov" <kirill@shutemov.name>]

On Fri, Jan 13, 2012 at 05:40:19PM +0900, KAMEZAWA Hiroyuki wrote:
> 
> From 1008e84d94245b1e7c4d237802ff68ff00757736 Mon Sep 17 00:00:00 2001
> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> Date: Thu, 12 Jan 2012 15:53:24 +0900
> Subject: [PATCH 3/7] memcg: remove PCG_MOVE_LOCK flag from pc->flags.
> 
> PCG_MOVE_LOCK bit is used for bit spinlock for avoiding race between
> memcg's account moving and page state statistics updates.
> 
> Considering page-statistics update, very hot path, this lock is
> taken only when someone is moving account (or PageTransHuge())
> And, now, all moving-account between memcgroups (by task-move)
> are serialized.
> 
> So, it seems too costly to have 1bit per page for this purpose.
> 
> This patch removes PCG_MOVE_LOCK and add hashed rwlock array
> instead of it. This works well enough. Even when we need to
> take the lock, we don't need to disable IRQ in hot path because
> of using rwlock.
> 
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

...

> +#define NR_MOVE_ACCOUNT_LOCKS	(NR_CPUS)
> +#define move_account_hash(page) ((page_to_pfn(page) % NR_MOVE_ACCOUNT_LOCKS))

You still tend to add too many parentheses into macros ;)

-- 
 Kirill A. Shutemov

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