From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail202.messagelabs.com (mail202.messagelabs.com [216.82.254.227]) by kanga.kvack.org (Postfix) with SMTP id 348256B003D for ; Thu, 26 Mar 2009 04:06:08 -0400 (EDT) Date: Thu, 26 Mar 2009 17:56:52 +0900 (JST) From: KOSAKI Motohiro Subject: Re: [patch 3/3] mm: keep pages from unevictable mappings off the LRU lists In-Reply-To: <20090326000100.GA5404@cmpxchg.org> References: <12135.1237805607@redhat.com> <20090326000100.GA5404@cmpxchg.org> Message-Id: <20090326175314.68F7.A69D9226@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: Johannes Weiner Cc: kosaki.motohiro@jp.fujitsu.com, David Howells , Andrew Morton , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Nick Piggin , Rik van Riel , Peter Zijlstra , MinChan Kim , Lee Schermerhorn List-ID: > On Mon, Mar 23, 2009 at 10:53:27AM +0000, David Howells wrote: > > Johannes Weiner wrote: > > > > > - if (page_is_file_cache(page)) > > > + if (mapping_unevictable(mapping)) > > > + add_page_to_unevictable_list(page); > > > + else if (page_is_file_cache(page)) > > > > It would be nice to avoid adding an extra test and branch in here. This > > function is used a lot, and quite often we know the answer to the first test > > before we even get here. > > Yes, I thought about that too. So I mounted a tmpfs and dd'd > /dev/zero to a file on it until it ran out of space (around 900M, > without swapping), deleted the file again. I did this in a tight loop > and profiled it. > > I couldn't think of a way that would excercise add_to_page_cache_lru() > more, I hope I didn't overlook anything, please correct if I am wrong. > > If I was not, than the extra checking for unevictable mappings doesn't > make a measurable difference. The function on the vanilla kernel had > a share of 0.2033%, on the patched kernel 0.1953%. May I ask the number of the cpu of your test box. In general, lock contention possibility depend on #ofCPUs. So, I and lee mainly talked about large box. -- 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