Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752216AbcDRPSE (ORCPT ); Mon, 18 Apr 2016 11:18:04 -0400 Received: from smtp.codeaurora.org ([198.145.29.96]:59183 "EHLO smtp.codeaurora.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752169AbcDRPR7 (ORCPT ); Mon, 18 Apr 2016 11:17:59 -0400 From: Vinayak Menon To: linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: akpm@linux-foundation.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, Vinayak Menon Subject: [PATCH] mm: make fault_around_bytes configurable Date: Mon, 18 Apr 2016 20:47:16 +0530 Message-Id: <1460992636-711-1-git-send-email-vinmenon@codeaurora.org> X-Mailer: git-send-email 1.8.2.1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4811 Lines: 116 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). 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. Make fault_around_bytes configurable so that it can be tuned to avoid performance degradation. Signed-off-by: Vinayak Menon --- mm/Kconfig | 10 ++++++++++ mm/memory.c | 2 +- 2 files changed, 11 insertions(+), 1 deletion(-) diff --git a/mm/Kconfig b/mm/Kconfig index f644106..e3476fd 100644 --- a/mm/Kconfig +++ b/mm/Kconfig @@ -681,6 +681,16 @@ config ZONE_DEVICE If FS_DAX is enabled, then say Y. +config FAULT_AROUND_BYTES + int + range 4096 65536 + default 65536 + help + The number of bytes to be mapped around the fault. The default + value of 64 kilobytes effectively disables faultaround on + architectures with page size >= 64k, considering the fact that + the feature is less relevant when page size is bigger than 4k. + config FRAME_VECTOR bool diff --git a/mm/memory.c b/mm/memory.c index 758b0b4..be06714 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -2939,7 +2939,7 @@ void do_set_pte(struct vm_area_struct *vma, unsigned long address, } static unsigned long fault_around_bytes __read_mostly = - rounddown_pow_of_two(65536); + rounddown_pow_of_two(CONFIG_FAULT_AROUND_BYTES); #ifdef CONFIG_DEBUG_FS static int fault_around_bytes_get(void *data, u64 *val) -- QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, hosted by The Linux Foundation