From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Mon, 28 Jul 2008 16:41:24 -0700 From: Andrew Morton Subject: Re: PERF: performance tests with the split LRU VM in -mm Message-Id: <20080728164124.8240eabe.akpm@linux-foundation.org> In-Reply-To: <20080728105742.50d6514e@cuia.bos.redhat.com> References: <20080724222510.3bbbbedc@bree.surriel.com> <20080728105742.50d6514e@cuia.bos.redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Rik van Riel Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org List-ID: On Mon, 28 Jul 2008 10:57:42 -0400 Rik van Riel wrote: > On Thu, 24 Jul 2008 22:25:10 -0400 > Rik van Riel wrote: > > > TEST 1: dd if=/dev/sda of=/dev/null bs=1M > > > > kernel speed swap used > > > > 2.6.26 111MB/s 500kB > > -mm 110MB/s 59MB (ouch, system noticably slower) > > noforce 111MB/s 128kB > > stream 108MB/s 0 (slight regression, not sure why yet) > > > > This patch shows that the split LRU VM in -mm has a problem > > with large streaming IOs: the working set gets pushed out of > > memory, which makes doing anything else during the big streaming > > IO kind of painful. > > > > However, either of the two patches posted fixes that problem, > > though at a slight performance penalty for the "stream" patch. > > OK, the throughput number with this test turns out not to mean > nearly as much as I thought. > > Switching off CPU frequency scaling, pinning the CPUs at the > highest speed, resulted in a throughput of only 102MB/s. > > My suspicion is that faster running code on the CPU results > in IOs being sent down to the device faster, resulting in > smaller IOs and lower throughput. > > This would be promising for the "stream" patch, which makes > choosing between the two patches harder :) > > Andrew, what is your preference between: > http://lkml.org/lkml/2008/7/15/465 > and > http://marc.info/?l=linux-mm&m=121683855132630&w=2 > Boy. They both seem rather hacky special-cases. But that doesn't mean that they're undesirable hacky special-cases. I guess the second one looks a bit more "algorithmic" and a bit less hacky-special-case. But it all depends on testing.. On a different topic, these: vmscan-give-referenced-active-and-unmapped-pages-a-second-trip-around-the-lru.patch vm-dont-run-touch_buffer-during-buffercache-lookups.patch have been floating about in -mm for ages, awaiting demonstration that they're a net benefit. But all of this new page-reclaim rework was built on top of those two patches and incorporates and retains them. I could toss them out, but that would require some rework and would partially invalidate previous testing and who knows, they _might_ be good patches. Or they might not be. What are your thoughts? -- 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