Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753976AbcDVORV (ORCPT ); Fri, 22 Apr 2016 10:17:21 -0400 Received: from mail-lf0-f42.google.com ([209.85.215.42]:33784 "EHLO mail-lf0-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753539AbcDVORU (ORCPT ); Fri, 22 Apr 2016 10:17:20 -0400 Date: Fri, 22 Apr 2016 17:17:16 +0300 From: "Kirill A. Shutemov" To: Minchan Kim Cc: Vinayak Menon , Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, dan.j.williams@intel.com, mgorman@suse.de, vbabka@suse.cz, kirill.shutemov@linux.intel.com, dave.hansen@linux.intel.com, hughd@google.com Subject: Re: [PATCH] mm: make fault_around_bytes configurable Message-ID: <20160422141716.GD7336@node.shutemov.name> References: <1460992636-711-1-git-send-email-vinmenon@codeaurora.org> <20160421170150.b492ffe35d073270b53f0e4d@linux-foundation.org> <5719E494.20302@codeaurora.org> <20160422140153.GA2840@blaptop> <20160422141141.GC7336@node.shutemov.name> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160422141141.GC7336@node.shutemov.name> User-Agent: Mutt/1.5.23.1 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 6280 Lines: 119 On Fri, Apr 22, 2016 at 05:11:41PM +0300, Kirill A. Shutemov wrote: > On Fri, Apr 22, 2016 at 11:02:16PM +0900, Minchan Kim wrote: > > On Fri, Apr 22, 2016 at 02:15:08PM +0530, Vinayak Menon wrote: > > > On 04/22/2016 05:31 AM, Andrew Morton wrote: > > > >On Mon, 18 Apr 2016 20:47:16 +0530 Vinayak Menon wrote: > > > > > > > >>Mapping pages around fault is found to cause performance degradation > > > >>in certain use cases. The test performed here is launch of 10 apps > > > >>one by one, doing something with the app each time, and then repeating > > > >>the same sequence once more, on an ARM 64-bit Android device with 2GB > > > >>of RAM. The time taken to launch the apps is found to be better when > > > >>fault around feature is disabled by setting fault_around_bytes to page > > > >>size (4096 in this case). > > > > > > > >Well that's one workload, and a somewhat strange one. What is the > > > >effect on other workloads (of which there are a lot!). > > > > > > > This workload emulates the way a user would use his mobile device, opening > > > an application, using it for some time, switching to next, and then coming > > > back to the same application later. Another stat which shows significant > > > degradation on Android with fault_around is device boot up time. I have not > > > tried any other workload other than these. > > > > > > >>The tests were done on 3.18 kernel. 4 extra vmstat counters were added > > > >>for debugging. pgpgoutclean accounts the clean pages reclaimed via > > > >>__delete_from_page_cache. pageref_activate, pageref_activate_vm_exec, > > > >>and pageref_keep accounts the mapped file pages activated and retained > > > >>by page_check_references. > > > >> > > > >>=== Without swap === > > > >> 3.18 3.18-fault_around_bytes=4096 > > > >>----------------------------------------------------------------------- > > > >>workingset_refault 691100 664339 > > > >>workingset_activate 210379 179139 > > > >>pgpgin 4676096 4492780 > > > >>pgpgout 163967 96711 > > > >>pgpgoutclean 1090664 990659 > > > >>pgalloc_dma 3463111 3328299 > > > >>pgfree 3502365 3363866 > > > >>pgactivate 568134 238570 > > > >>pgdeactivate 752260 392138 > > > >>pageref_activate 315078 121705 > > > >>pageref_activate_vm_exec 162940 55815 > > > >>pageref_keep 141354 51011 > > > >>pgmajfault 24863 23633 > > > >>pgrefill_dma 1116370 544042 > > > >>pgscan_kswapd_dma 1735186 1234622 > > > >>pgsteal_kswapd_dma 1121769 1005725 > > > >>pgscan_direct_dma 12966 1090 > > > >>pgsteal_direct_dma 6209 967 > > > >>slabs_scanned 1539849 977351 > > > >>pageoutrun 1260 1333 > > > >>allocstall 47 7 > > > >> > > > >>=== With swap === > > > >> 3.18 3.18-fault_around_bytes=4096 > > > >>----------------------------------------------------------------------- > > > >>workingset_refault 597687 878109 > > > >>workingset_activate 167169 254037 > > > >>pgpgin 4035424 5157348 > > > >>pgpgout 162151 85231 > > > >>pgpgoutclean 928587 1225029 > > > >>pswpin 46033 17100 > > > >>pswpout 237952 127686 > > > >>pgalloc_dma 3305034 3542614 > > > >>pgfree 3354989 3592132 > > > >>pgactivate 626468 355275 > > > >>pgdeactivate 990205 771902 > > > >>pageref_activate 294780 157106 > > > >>pageref_activate_vm_exec 141722 63469 > > > >>pageref_keep 121931 63028 > > > >>pgmajfault 67818 45643 > > > >>pgrefill_dma 1324023 977192 > > > >>pgscan_kswapd_dma 1825267 1720322 > > > >>pgsteal_kswapd_dma 1181882 1365500 > > > >>pgscan_direct_dma 41957 9622 > > > >>pgsteal_direct_dma 25136 6759 > > > >>slabs_scanned 689575 542705 > > > >>pageoutrun 1234 1538 > > > >>allocstall 110 26 > > > >> > > > >>Looks like with fault_around, there is more pressure on reclaim because > > > >>of the presence of more mapped pages, resulting in more IO activity, > > > >>more faults, more swapping, and allocstalls. > > > > > > > >A few of those things did get a bit worse? > > > I think some numbers (like workingset, pgpgin, pgpgoutclean etc) looks > > > better with fault_around because, increased number of mapped pages is > > > resulting in less number of file pages being reclaimed (pageref_activate, > > > pageref_activate_vm_exec, pageref_keep above), but increased swapping. > > > Latency numbers are far bad with fault_around_bytes + swap, possibly because > > > of increased swapping, decrease in kswapd efficiency and increase in > > > allocstalls. > > > So the problem looks to be that unwanted pages are mapped around the fault > > > and page_check_references is unaware of this. > > > > The page_check_references makes difference only when pte has marked access_bit. > > > > enum page_references page_check_references(struct page *page) > > { > > referenced_ptes = page_referenced(page); > > if (referenced_ptes) { > > ... > > return PAGEREF_ACTIVATE > > } > > } > > > > But map_pages doesn't mark ahead pages as pte_mkyoung. IOW, ptes are already > > pte_mkold. So, I think page_check_reference shouldn't make any difference. > > Actually, I've checked and mk_pte() produces young ptes for me. Not sure > why. Ah. Okay, _PAGE_ACCESSED included into pgprot mask, which is reasonable to have if you handle page fault for the address. But it should be adjusted for faultaround. -- Kirill A. Shutemov