From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758082AbYFGBGU (ORCPT ); Fri, 6 Jun 2008 21:06:20 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754017AbYFGBFY (ORCPT ); Fri, 6 Jun 2008 21:05:24 -0400 Received: from smtp1.linux-foundation.org ([140.211.169.13]:37832 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754279AbYFGBFI (ORCPT ); Fri, 6 Jun 2008 21:05:08 -0400 Date: Fri, 6 Jun 2008 18:04:30 -0700 From: Andrew Morton To: Rik van Riel Cc: linux-kernel@vger.kernel.org, lee.schermerhorn@hp.com, kosaki.motohiro@jp.fujitsu.com, minchan.kim@gmail.com, Lee.Schermerhorn@hp.com, Hugh Dickins Subject: Re: [PATCH -mm 04/25] free swap space on swap-in/activation Message-Id: <20080606180430.38bf1d82.akpm@linux-foundation.org> In-Reply-To: <20080606202858.570020389@redhat.com> References: <20080606202838.390050172@redhat.com> <20080606202858.570020389@redhat.com> X-Mailer: Sylpheed version 2.2.4 (GTK+ 2.8.20; i486-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 06 Jun 2008 16:28:42 -0400 Rik van Riel wrote: > From: Rik van Riel > > Free swap cache entries when swapping in pages if vm_swap_full() > [swap space > 1/2 used]. Uses new pagevec to reduce pressure > on locks. > > Signed-off-by: Rik van Riel > Signed-off-by: Lee Schermerhorn > Signed-off-by: MinChan Kim > > --- > include/linux/pagevec.h | 1 + > include/linux/swap.h | 6 ++++++ > mm/swap.c | 18 ++++++++++++++++++ > mm/swapfile.c | 25 ++++++++++++++++++++++--- > mm/vmscan.c | 7 +++++++ > 5 files changed, 54 insertions(+), 3 deletions(-) > > Index: linux-2.6.26-rc2-mm1/mm/vmscan.c > =================================================================== > --- linux-2.6.26-rc2-mm1.orig/mm/vmscan.c 2008-05-23 14:21:33.000000000 -0400 > +++ linux-2.6.26-rc2-mm1/mm/vmscan.c 2008-05-23 14:21:33.000000000 -0400 > @@ -619,6 +619,9 @@ free_it: > continue; > > activate_locked: > + /* Not a candidate for swapping, so reclaim swap space. */ > + if (PageSwapCache(page) && vm_swap_full()) The patch puts rather a lot of pressure onto vm_swap_full(). We might want to look into optimising that. - Is the 50% thing optimum? Could go higher and perhaps should be based on amount-of-memory. - Can precalculate the fraction rather than doing it inline all the time. - Can make total_swap_pages __read_mostly and have a think about nr_swap_pages too. - Can completely optimise the thing away if !CONFIG_SWAP. Has all this code been tested with CONFIG_SWAP=n? > Index: linux-2.6.26-rc2-mm1/mm/swap.c > =================================================================== > --- linux-2.6.26-rc2-mm1.orig/mm/swap.c 2008-05-23 14:21:33.000000000 -0400 > +++ linux-2.6.26-rc2-mm1/mm/swap.c 2008-05-23 14:21:33.000000000 -0400 > @@ -443,6 +443,24 @@ void pagevec_strip(struct pagevec *pvec) > } > } > > +/* > + * Try to free swap space from the pages in a pagevec > + */ > +void pagevec_swap_free(struct pagevec *pvec) > +{ > + int i; > + > + for (i = 0; i < pagevec_count(pvec); i++) { > + struct page *page = pvec->pages[i]; > + > + if (PageSwapCache(page) && !TestSetPageLocked(page)) { > + if (PageSwapCache(page)) > + remove_exclusive_swap_page_ref(page); > + unlock_page(page); > + } > + } > +} What's going on here. Normally we'll bump a page's refcount to account for its presence in a pagevec. This code doesn't do that. Is it safe? If so, how come? Suitable code comments should be added which explain this unusual and dangerous optimisation. Or fix the bug :)