From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail172.messagelabs.com (mail172.messagelabs.com [216.82.254.3]) by kanga.kvack.org (Postfix) with ESMTP id 504D86B00D4 for ; Tue, 19 Oct 2010 01:08:45 -0400 (EDT) Date: Tue, 19 Oct 2010 14:03:38 +0900 From: Daisuke Nishimura Subject: Re: [PATCH v3 04/11] memcg: add lock to synchronize page accounting and migration Message-Id: <20101019140338.9fd664bc.nishimura@mxp.nes.nec.co.jp> In-Reply-To: <1287448784-25684-5-git-send-email-gthelen@google.com> References: <1287448784-25684-1-git-send-email-gthelen@google.com> <1287448784-25684-5-git-send-email-gthelen@google.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: Greg Thelen Cc: Andrew Morton , linux-kernel@vger.kernel.org, linux-mm@kvack.org, containers@lists.osdl.org, Andrea Righi , Balbir Singh , KAMEZAWA Hiroyuki , Minchan Kim , Ciju Rajan K , David Rientjes , Daisuke Nishimura List-ID: On Mon, 18 Oct 2010 17:39:37 -0700 Greg Thelen wrote: > From: KAMEZAWA Hiroyuki > > From: KAMEZAWA Hiroyuki > > Introduce a new bit spin lock, PCG_MOVE_LOCK, to synchronize > the page accounting and migration code. This reworks the > locking scheme of _update_stat() and _move_account() by > adding new lock bit PCG_MOVE_LOCK, which is always taken > under IRQ disable. > > 1. If pages are being migrated from a memcg, then updates to > that memcg page statistics are protected by grabbing > PCG_MOVE_LOCK using move_lock_page_cgroup(). In an > upcoming commit, memcg dirty page accounting will be > updating memcg page accounting (specifically: num > writeback pages) from IRQ context (softirq). Avoid a > deadlocking nested spin lock attempt by disabling irq on > the local processor when grabbing the PCG_MOVE_LOCK. > > 2. lock for update_page_stat is used only for avoiding race > with move_account(). So, IRQ awareness of > lock_page_cgroup() itself is not a problem. The problem > is between mem_cgroup_update_page_stat() and > mem_cgroup_move_account_page(). > > Trade-off: > * Changing lock_page_cgroup() to always disable IRQ (or > local_bh) has some impacts on performance and I think > it's bad to disable IRQ when it's not necessary. > * adding a new lock makes move_account() slower. Score is > here. > > Performance Impact: moving a 8G anon process. > > Before: > real 0m0.792s > user 0m0.000s > sys 0m0.780s > > After: > real 0m0.854s > user 0m0.000s > sys 0m0.842s > > This score is bad but planned patches for optimization can reduce > this impact. > > Signed-off-by: KAMEZAWA Hiroyuki > Signed-off-by: Greg Thelen This approach is more straightforward and easy to understand. Acked-by: Daisuke Nishimura -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org