Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753454Ab0A1IJp (ORCPT ); Thu, 28 Jan 2010 03:09:45 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752920Ab0A1IJo (ORCPT ); Thu, 28 Jan 2010 03:09:44 -0500 Received: from mail-pw0-f42.google.com ([209.85.160.42]:59298 "EHLO mail-pw0-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752327Ab0A1IJn convert rfc822-to-8bit (ORCPT ); Thu, 28 Jan 2010 03:09:43 -0500 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type:content-transfer-encoding; b=oG+mJyKAZ7CfkVHT7erXSOl9MhxDjkzO/Xc7G/zUmj5QwH5mjnvhRHKKY44bYpua14 LZ41n36poXYyUtv+EFlLJcU1IaZ90bTCtcNSAK1OmK81FwkjoGemgvoUaPWK6QWpbnpI AVRI2mOe7DsPgPjjwPCalienx2KZYbpgG7mXw= MIME-Version: 1.0 In-Reply-To: References: <20100120215536.GN27212@frostnet.net> <20100121054734.GC24236@localhost> <28c262361001262309x332a895aoa906dda0bc040859@mail.gmail.com> Date: Thu, 28 Jan 2010 17:09:43 +0900 Message-ID: <28c262361001280009u509f169dnc558d013150ca00b@mail.gmail.com> Subject: Re: [PATCH] mm/readahead.c: update the LRU positions of in-core pages, too From: Minchan Kim To: Steve VanDeBogart Cc: Wu Fengguang , Chris Frost , Andrew Morton , Steve Dickson , David Howells , Xu Chenfeng , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3148 Lines: 96 On Thu, Jan 28, 2010 at 4:16 PM, Steve VanDeBogart wrote: > On Wed, 27 Jan 2010, Minchan Kim wrote: > >> This patch effect happens when inactive file list is small, I think. >> It means it's high memory pressure. so if we move ra pages into > > This patch does the same thing regardless of memory pressure - it > doesn't just apply in high memory pressure situations.  Is your concern > that in high memory pressure situations this patch with make things worse? Yes. > >> head of inactive list, other application which require free page urgently >> suffer from latency or are killed. > > I don't think this patch will affect the number of pages reclaimed, only > which pages are reclaimed.  In extreme cases it could increase the time Most likely. But it can affect the number of pages reclaimed at sometime. For example, scanning window size for reclaim = 5. P : hard reclaimable page R : readaheaded page(easily reclaimable page) without this patch HEAD-P - P - P - P ................ - P - R -R -R -R -R- TAIL reclaimed pages : 5 with this patch HEAD-R-R-R-R-R .................... - P -P -P -P -P -P -TAIL reclaimed pages : 0 => might be OOMed. Yes. It's very extreme example. it is just for explanation. :) > needed to reclaim that many pages, but the inactive list would have to be > very short. I think short inactive list means now we are suffering from shortage of free memory. So I think it would be better to discard ra pages rather than OOMed. > >> If VM don't have this patch, of course ra pages are discarded and >> then I/O performance would be bad. but as I mentioned, it's time >> high memory pressure. so I/O performance low makes system >> natural throttling. It can help out of  system memory pressure. > > Even in low memory situations, improving I/O performance can help the > overall system performance.  For example if most of the inactive list is > dirty, needlessly discarding pages, just to refetch them will clog > I/O and increase the time needed to write out the dirty pages. Yes. That's what I said. But my point is that it makes system I/O throttling by clogging I/O naturally. It can prevent fast consumption of memory. Actually I think mm don't have to consider I/O throttling as far as possible. It's role of I/O subsystem. but it's not real. There are some codes for I/O throttling in mm. > >> In summary I think it's good about viewpoint of I/O but I am not sure >> it's good about viewpoint of system. > > In this case, I think what's good for I/O is good for the system. > Please help me understand if I am missing something.  Thanks You didn't missed anything. :) I don't know how this patch affect in low memory situation. What we just need is experiment which is valuable. Wu have a catch in my concern and are making new version. I am looking forward to that. > > -- > Steve > -- Kind regards, Minchan Kim -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/