From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755352AbYFGT4z (ORCPT ); Sat, 7 Jun 2008 15:56:55 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751713AbYFGT4s (ORCPT ); Sat, 7 Jun 2008 15:56:48 -0400 Received: from mx1.redhat.com ([66.187.233.31]:55433 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751322AbYFGT4r (ORCPT ); Sat, 7 Jun 2008 15:56:47 -0400 Date: Sat, 7 Jun 2008 15:56:20 -0400 From: Rik van Riel To: Andrew Morton Cc: linux-kernel@vger.kernel.org, lee.schermerhorn@hp.com, kosaki.motohiro@jp.fujitsu.com, minchan.kim@gmail.com, Hugh Dickins Subject: Re: [PATCH -mm 04/25] free swap space on swap-in/activation Message-ID: <20080607155620.733f1b01@bree.surriel.com> In-Reply-To: <20080606180430.38bf1d82.akpm@linux-foundation.org> References: <20080606202838.390050172@redhat.com> <20080606202858.570020389@redhat.com> <20080606180430.38bf1d82.akpm@linux-foundation.org> Organization: Red Hat, Inc. X-Mailer: Claws Mail 3.0.2 (GTK+ 2.10.4; x86_64-redhat-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, 6 Jun 2008 18:04:30 -0700 Andrew Morton wrote: > 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. I do not know if 50% is optimum. It is just what the upstream kernel has had since 2.4.10 or so. Before that it used to be 75%. This same percentage is used to free swap spaces at swapin time. > - Can make total_swap_pages __read_mostly and have a think about > nr_swap_pages too. I wonder if we wouldn't be off best simply placing the two on their own cache line. After all, they are often handled together. I believe that should be a separate patch though, since I am not changing that situation from what is already upstream and this patch series contains more than enough stuff already. > - Can completely optimise the thing away if !CONFIG_SWAP. > > > Has all this code been tested with CONFIG_SWAP=n? With CONFIG_SWAP=n the macro PageSwapCache(page) will always be declared false due to the declarations in page-flags.h. That means that vm_swap_full() will be evaluated and the compiler should leave it out. #ifdef CONFIG_SWAP PAGEFLAG(SwapCache, swapcache) #else PAGEFLAG_FALSE(SwapCache) #endif > > +void pagevec_swap_free(struct pagevec *pvec) > 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? It is safe because the callers already hold an extra reference to each page. I have added a full kerneldoc comment to this function to explain that. -- All rights reversed.