From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail143.messagelabs.com (mail143.messagelabs.com [216.82.254.35]) by kanga.kvack.org (Postfix) with ESMTP id 2C8146B003D for ; Thu, 26 Feb 2009 12:15:56 -0500 (EST) Date: Thu, 26 Feb 2009 17:15:49 +0000 From: Mel Gorman Subject: Re: [PATCH 20/20] Get rid of the concept of hot/cold page freeing Message-ID: <20090226171549.GH32756@csn.ul.ie> References: <1235344649-18265-21-git-send-email-mel@csn.ul.ie> <20090223013723.1d8f11c1.akpm@linux-foundation.org> <20090223233030.GA26562@csn.ul.ie> <20090223155313.abd41881.akpm@linux-foundation.org> <20090224115126.GB25151@csn.ul.ie> <20090224160103.df238662.akpm@linux-foundation.org> <20090225160124.GA31915@csn.ul.ie> <20090225081954.8776ba9b.akpm@linux-foundation.org> <20090226163751.GG32756@csn.ul.ie> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org To: Christoph Lameter Cc: Andrew Morton , linux-mm@kvack.org, penberg@cs.helsinki.fi, riel@redhat.com, kosaki.motohiro@jp.fujitsu.com, hannes@cmpxchg.org, npiggin@suse.de, linux-kernel@vger.kernel.org, ming.m.lin@intel.com, yanmin_zhang@linux.intel.com List-ID: On Thu, Feb 26, 2009 at 12:00:22PM -0500, Christoph Lameter wrote: > On Thu, 26 Feb 2009, Mel Gorman wrote: > > > The known-to-be-zeroed pages is interesting and something I tried but didn't > > get far enough with. One patch I did but didn't release would zero pages on > > the free path if the was process exiting or if it was kswapd. It tracked if > > the page was zero using page->index to record the order of the zerod page. On > > allocation, it would check index and if a matching order, would not zero a > > second time. I got this working for order-0 pages reliably but it didn't gain > > anything because we were zeroing even more than we had to in the free path. > > I tried the general use of a pool of zeroed pages back in 2005. Zeroing > made sense only if the code allocating the page did not immediately touch > the cachelines of the page. Any feeling as to how often this was the case? > The more cachelines were touched the less the > benefit. If the page is written to immediately afterwards then the zeroing > simply warms up the caches. > > page table pages are different. We may only write to a few cachelines in > the page. There it makes sense and that is why we have the special > quicklists there. > > > If pagetable pages were known to be zero and handed back to the allocator > > that remember zerod pages, I bet we'd get a win. > > We have quicklists that do this on various platforms. > Indeed, any gain if it existed would be avoiding zeroing the pages used by userspace. The cleanup would be reducing the amount of architecture-specific code. I reckon it's worth an investigate but there is still other lower-lying fruit. -- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab -- 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