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 35BE16B0085 for ; Fri, 8 Oct 2010 00:55:22 -0400 (EDT) Date: Thu, 7 Oct 2010 21:55:56 -0700 From: Andrew Morton Subject: Re: [PATCH v2] memcg: reduce lock time at move charge (Was Re: [PATCH 04/10] memcg: disable local interrupts in lock_page_cgroup() Message-Id: <20101007215556.21412ae6.akpm@linux-foundation.org> In-Reply-To: <20101008133712.2a836331.kamezawa.hiroyu@jp.fujitsu.com> References: <1286175485-30643-1-git-send-email-gthelen@google.com> <1286175485-30643-5-git-send-email-gthelen@google.com> <20101005160332.GB9515@barrios-desktop> <20101007093545.429fe04a.kamezawa.hiroyu@jp.fujitsu.com> <20101007105456.d86d8092.nishimura@mxp.nes.nec.co.jp> <20101007111743.322c3993.kamezawa.hiroyu@jp.fujitsu.com> <20101007152111.df687a62.kamezawa.hiroyu@jp.fujitsu.com> <20101007162811.c3a35be9.nishimura@mxp.nes.nec.co.jp> <20101007164204.83b207c6.kamezawa.hiroyu@jp.fujitsu.com> <20101007170405.27ed964c.kamezawa.hiroyu@jp.fujitsu.com> <20101007161454.84570cf9.akpm@linux-foundation.org> <20101008133712.2a836331.kamezawa.hiroyu@jp.fujitsu.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: KAMEZAWA Hiroyuki Cc: Daisuke Nishimura , Minchan Kim , Greg Thelen , linux-kernel@vger.kernel.org, linux-mm@kvack.org, containers@lists.osdl.org, Andrea Righi , Balbir Singh List-ID: On Fri, 8 Oct 2010 13:37:12 +0900 KAMEZAWA Hiroyuki wrote: > On Thu, 7 Oct 2010 16:14:54 -0700 > Andrew Morton wrote: > > > On Thu, 7 Oct 2010 17:04:05 +0900 > > KAMEZAWA Hiroyuki wrote: > > > > > Now, at task migration among cgroup, memory cgroup scans page table and moving > > > account if flags are properly set. > > > > > > The core code, mem_cgroup_move_charge_pte_range() does > > > > > > pte_offset_map_lock(); > > > for all ptes in a page table: > > > 1. look into page table, find_and_get a page > > > 2. remove it from LRU. > > > 3. move charge. > > > 4. putback to LRU. put_page() > > > pte_offset_map_unlock(); > > > > > > for pte entries on a 3rd level? page table. > > > > > > This pte_offset_map_lock seems a bit long. This patch modifies a rountine as > > > > > > for 32 pages: pte_offset_map_lock() > > > find_and_get a page > > > record it > > > pte_offset_map_unlock() > > > for all recorded pages > > > isolate it from LRU. > > > move charge > > > putback to LRU > > > for all recorded pages > > > put_page() > > > > The patch makes the code larger, more complex and slower! > > > > Slower ? Sure. It walks the same data three times, potentially causing thrashing in the L1 cache. It takes and releases locks at a higher frequency. It increases the text size. -- 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