From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758745AbZE0B2T (ORCPT ); Tue, 26 May 2009 21:28:19 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756673AbZE0B2D (ORCPT ); Tue, 26 May 2009 21:28:03 -0400 Received: from cmpxchg.org ([85.214.51.133]:44205 "EHLO cmpxchg.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754600AbZE0B2B (ORCPT ); Tue, 26 May 2009 21:28:01 -0400 Date: Wed, 27 May 2009 03:26:58 +0200 From: Johannes Weiner To: KAMEZAWA Hiroyuki Cc: "linux-mm@kvack.org" , "balbir@linux.vnet.ibm.com" , "nishimura@mxp.nes.nec.co.jp" , "hugh.dickins@tiscali.co.uk" , "linux-kernel@vger.kernel.org" Subject: Re: [RFC][PATCH 5/5] (experimental) chase and free cache only swap Message-ID: <20090527012658.GA9692@cmpxchg.org> References: <20090526121259.b91b3e9d.kamezawa.hiroyu@jp.fujitsu.com> <20090526121834.dd9a4193.kamezawa.hiroyu@jp.fujitsu.com> <20090526181359.GB2843@cmpxchg.org> <20090527090813.a0e436f8.kamezawa.hiroyu@jp.fujitsu.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090527090813.a0e436f8.kamezawa.hiroyu@jp.fujitsu.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, May 27, 2009 at 09:08:13AM +0900, KAMEZAWA Hiroyuki wrote: > On Tue, 26 May 2009 20:14:00 +0200 > Johannes Weiner wrote: > > > On Tue, May 26, 2009 at 12:18:34PM +0900, KAMEZAWA Hiroyuki wrote: > > > > > > From: KAMEZAWA Hiroyuki > > > > > > Just a trial/example patch. > > > I'd like to consider more. Better implementation idea is welcome. > > > > > > When the system does swap-in/swap-out repeatedly, there are > > > cache-only swaps in general. > > > Typically, > > > - swapped out in past but on memory now while vm_swap_full() returns true > > > pages are cache-only swaps. (swap_map has no references.) > > > > > > This cache-only swaps can be an obstacles for smooth page reclaiming. > > > Current implemantation is very naive, just scan & free. > > > > I think we can just remove that vm_swap_full() check in do_swap_page() > > and try to remove the page from swap cache unconditionally. > > > I'm not sure why reclaim swap entry only at write fault. How do you come to that conclusion? Do you mean the current code does that? Did you understand that I suggested that? > > If it's still mapped someplace else, we let it cached. If not, there > > is not much use for keeping it around and we free it. > > > yes. > > > When I removed it and did benchmarks, I couldn't spot any difference > > in the timings, though. Did you measure the benefits of your patch > > somehow? > My patche has no "performance benefit". (My patch description may be bad.) > I just checked that cache-only-swap can be big.(by sysrq-m) > > Even when we remove vm_swap_full() in do_swap_page(), > swapin-readahead + trylock-at-zap + vmscan makes "unused" swap caches easily. > It reaches 1M in 2hours test of heavy swap program. Ouch. > > According to the git history tree, vm_swap_full() was initially only > > used to aggressively drop cache entries even when they are mapped. > > > > Rik put it into vmscan to reclaim swap cache _at all_ for activated > > pages. But I think unconditionally dropping the cache entry makes > > sense if the page gets shuffled around on the LRU list. Better to > > re-allocate a swap slot close to the new LRU buddies on the next scan. > > > > And having this all covered, the need for the scanning your patch does > > should be gone, unless I missed something. > > > Considering memcg, global lru scanning is no help ;( > And I'm writing this patch for memcg. Oh, sorry. That makes sense of course. 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 ESMTP id 02E986B004F for ; Tue, 26 May 2009 21:27:32 -0400 (EDT) Date: Wed, 27 May 2009 03:26:58 +0200 From: Johannes Weiner Subject: Re: [RFC][PATCH 5/5] (experimental) chase and free cache only swap Message-ID: <20090527012658.GA9692@cmpxchg.org> References: <20090526121259.b91b3e9d.kamezawa.hiroyu@jp.fujitsu.com> <20090526121834.dd9a4193.kamezawa.hiroyu@jp.fujitsu.com> <20090526181359.GB2843@cmpxchg.org> <20090527090813.a0e436f8.kamezawa.hiroyu@jp.fujitsu.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090527090813.a0e436f8.kamezawa.hiroyu@jp.fujitsu.com> Sender: owner-linux-mm@kvack.org To: KAMEZAWA Hiroyuki Cc: "linux-mm@kvack.org" , "balbir@linux.vnet.ibm.com" , "nishimura@mxp.nes.nec.co.jp" , "hugh.dickins@tiscali.co.uk" , "linux-kernel@vger.kernel.org" List-ID: On Wed, May 27, 2009 at 09:08:13AM +0900, KAMEZAWA Hiroyuki wrote: > On Tue, 26 May 2009 20:14:00 +0200 > Johannes Weiner wrote: > > > On Tue, May 26, 2009 at 12:18:34PM +0900, KAMEZAWA Hiroyuki wrote: > > > > > > From: KAMEZAWA Hiroyuki > > > > > > Just a trial/example patch. > > > I'd like to consider more. Better implementation idea is welcome. > > > > > > When the system does swap-in/swap-out repeatedly, there are > > > cache-only swaps in general. > > > Typically, > > > - swapped out in past but on memory now while vm_swap_full() returns true > > > pages are cache-only swaps. (swap_map has no references.) > > > > > > This cache-only swaps can be an obstacles for smooth page reclaiming. > > > Current implemantation is very naive, just scan & free. > > > > I think we can just remove that vm_swap_full() check in do_swap_page() > > and try to remove the page from swap cache unconditionally. > > > I'm not sure why reclaim swap entry only at write fault. How do you come to that conclusion? Do you mean the current code does that? Did you understand that I suggested that? > > If it's still mapped someplace else, we let it cached. If not, there > > is not much use for keeping it around and we free it. > > > yes. > > > When I removed it and did benchmarks, I couldn't spot any difference > > in the timings, though. Did you measure the benefits of your patch > > somehow? > My patche has no "performance benefit". (My patch description may be bad.) > I just checked that cache-only-swap can be big.(by sysrq-m) > > Even when we remove vm_swap_full() in do_swap_page(), > swapin-readahead + trylock-at-zap + vmscan makes "unused" swap caches easily. > It reaches 1M in 2hours test of heavy swap program. Ouch. > > According to the git history tree, vm_swap_full() was initially only > > used to aggressively drop cache entries even when they are mapped. > > > > Rik put it into vmscan to reclaim swap cache _at all_ for activated > > pages. But I think unconditionally dropping the cache entry makes > > sense if the page gets shuffled around on the LRU list. Better to > > re-allocate a swap slot close to the new LRU buddies on the next scan. > > > > And having this all covered, the need for the scanning your patch does > > should be gone, unless I missed something. > > > Considering memcg, global lru scanning is no help ;( > And I'm writing this patch for memcg. Oh, sorry. That makes sense of course. -- 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