Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Wed, 25 Jul 2001 01:06:41 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Wed, 25 Jul 2001 01:06:30 -0400 Received: from vasquez.zip.com.au ([203.12.97.41]:59151 "EHLO vasquez.zip.com.au") by vger.kernel.org with ESMTP id ; Wed, 25 Jul 2001 01:06:18 -0400 Message-ID: <3B5E554E.86FDA41F@zip.com.au> Date: Wed, 25 Jul 2001 15:12:46 +1000 From: Andrew Morton X-Mailer: Mozilla 4.76 [en] (X11; U; Linux 2.4.7-pre6 i686) X-Accept-Language: en MIME-Version: 1.0 To: Marcelo Tosatti CC: Rik van Riel , Daniel Phillips , linux-kernel@vger.kernel.org, Ben LaHaise , Mike Galbraith Subject: Re: [RFC] Optimization for use-once pages In-Reply-To:

Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Original-Recipient: rfc822;linux-kernel-outgoing Marcelo Tosatti wrote: > > Daniel's patch adds "drop behind" (that is, adding swapcache > pages to the inactive dirty) behaviour to swapcache pages. In some *brief* testing here, it appears that the use-once changes make an improvement for light-medium workloads. With swap-intensive workloads, the (possibly accidental) changes to swapcache aging in fact improve things a lot, and use-once makes things a little worse. This is a modified Galbraith test: 64 megs of RAM, `make -j12 bzImage', dual CPU: 2.4.7: 6:54 2.4.7+Daniel's patch 6:06 2.4.7+the below patch 5:56 --- mm/swap.c 2001/01/23 08:37:48 1.3 +++ mm/swap.c 2001/07/25 04:08:59 @@ -234,8 +234,8 @@ DEBUG_ADD_PAGE add_page_to_active_list(page); /* This should be relatively rare */ - if (!page->age) - deactivate_page_nolock(page); + deactivate_page_nolock(page); + page->age = 0; spin_unlock(&pagemap_lru_lock); } This change to lru_cache_add() is the only change made to 2.4.7, and it provides the 17% speedup for this swap-intensive load. With the same setup, running a `grep -r /usr/src' in parallel with a `make -j3 bzImage', the `make -j3' takes: 2.4.7: 5:13 2.4.7+Daniel: 5:03 2.4.7+the above patch: 5:16 With the same setup, running a `grep -r /usr/src' in parallel with a `make -j1 bzImage', the `make -j1' takes: 2.4.7: 9:25 2.4.7+Daniel: 8:55 2.4.7+the above patch: 9:35 So with lighter loads, use-once is starting to provide benefit, and the deactivation is too aggressive. > This is a _new_ thing, and I would like to know how that is changing the > whole VM behaviour.. Sure. Daniel's patch radically changes the aging of swapcache and other pages, and with some workloads it appears that it is this change which brings about the performance increase, rather than the intended use-once stuff. I suspect the right balance here is to take use-once, but *not* take its changes to lru_cache_add(). That's a separate thing. Seems that lru_cache_add() is making decisions at a too-low level, and they are sometimes wrong. The decision as to what age to give the page and whether it should be activated needs to be made at a higher level. - - 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/