From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f71.google.com (mail-pa0-f71.google.com [209.85.220.71]) by kanga.kvack.org (Postfix) with ESMTP id DE4DB6B0263 for ; Wed, 31 Aug 2016 11:44:40 -0400 (EDT) Received: by mail-pa0-f71.google.com with SMTP id ag5so96297120pad.2 for ; Wed, 31 Aug 2016 08:44:40 -0700 (PDT) Received: from mga05.intel.com (mga05.intel.com. [192.55.52.43]) by mx.google.com with ESMTPS id d131si472204pfg.5.2016.08.31.08.44.39 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 31 Aug 2016 08:44:40 -0700 (PDT) From: "Huang\, Ying" Subject: Re: [PATCH -v2] mm: Don't use radix tree writeback tags for pages in swap cache References: <1472578089-5560-1-git-send-email-ying.huang@intel.com> <20160831091459.GY8119@techsingularity.net> <87oa49m0hn.fsf@yhuang-mobile.sh.intel.com> <20160831153908.GA8119@techsingularity.net> Date: Wed, 31 Aug 2016 08:44:39 -0700 In-Reply-To: <20160831153908.GA8119@techsingularity.net> (Mel Gorman's message of "Wed, 31 Aug 2016 16:39:08 +0100") Message-ID: <87r395kkns.fsf@yhuang-mobile.sh.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Sender: owner-linux-mm@kvack.org List-ID: To: Mel Gorman Cc: "Huang, Ying" , Andrew Morton , tim.c.chen@intel.com, dave.hansen@intel.com, andi.kleen@intel.com, aaron.lu@intel.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Hugh Dickins , Shaohua Li , Minchan Kim , Rik van Riel , Tejun Heo , Wu Fengguang Mel Gorman writes: > On Wed, Aug 31, 2016 at 08:17:24AM -0700, Huang, Ying wrote: >> Mel Gorman writes: >> >> > On Tue, Aug 30, 2016 at 10:28:09AM -0700, Huang, Ying wrote: >> >> From: Huang Ying >> >> >> >> File pages use a set of radix tree tags (DIRTY, TOWRITE, WRITEBACK, >> >> etc.) to accelerate finding the pages with a specific tag in the radix >> >> tree during inode writeback. But for anonymous pages in the swap >> >> cache, there is no inode writeback. So there is no need to find the >> >> pages with some writeback tags in the radix tree. It is not necessary >> >> to touch radix tree writeback tags for pages in the swap cache. >> >> >> >> Per Rik van Riel's suggestion, a new flag AS_NO_WRITEBACK_TAGS is >> >> introduced for address spaces which don't need to update the writeback >> >> tags. The flag is set for swap caches. It may be used for DAX file >> >> systems, etc. >> >> >> >> With this patch, the swap out bandwidth improved 22.3% (from ~1.2GB/s to >> >> ~ 1.48GBps) in the vm-scalability swap-w-seq test case with 8 processes. >> >> The test is done on a Xeon E5 v3 system. The swap device used is a RAM >> >> simulated PMEM (persistent memory) device. The improvement comes from >> >> the reduced contention on the swap cache radix tree lock. To test >> >> sequential swapping out, the test case uses 8 processes, which >> >> sequentially allocate and write to the anonymous pages until RAM and >> >> part of the swap device is used up. >> >> >> >> Details of comparison is as follow, >> >> >> >> base base+patch >> >> ---------------- -------------------------- >> >> %stddev %change %stddev >> >> \ | \ >> >> 2506952 A+- 2% +28.1% 3212076 A+- 7% vm-scalability.throughput >> >> 1207402 A+- 7% +22.3% 1476578 A+- 6% vmstat.swap.so >> >> 10.86 A+- 12% -23.4% 8.31 A+- 16% perf-profile.cycles-pp._raw_spin_lock_irq.__add_to_swap_cache.add_to_swap_cache.add_to_swap.shrink_page_list >> >> 10.82 A+- 13% -33.1% 7.24 A+- 14% perf-profile.cycles-pp._raw_spin_lock_irqsave.__remove_mapping.shrink_page_list.shrink_inactive_list.shrink_zone_memcg >> >> 10.36 A+- 11% -100.0% 0.00 A+- -1% perf-profile.cycles-pp._raw_spin_lock_irqsave.__test_set_page_writeback.bdev_write_page.__swap_writepage.swap_writepage >> >> 10.52 A+- 12% -100.0% 0.00 A+- -1% perf-profile.cycles-pp._raw_spin_lock_irqsave.test_clear_page_writeback.end_page_writeback.page_endio.pmem_rw_page >> >> >> > >> > I didn't see anything wrong with the patch but it's worth highlighting >> > that this hunk means we are now out of GFP bits. >> >> Sorry, I don't know whether I understand your words. It is something >> about, >> >> __GFP_BITS_SHIFT == 26 >> >> So remainning bits in mapping_flags is 6. And now the latest bit is >> used for the flag introduced in the patch? >> > > __GFP_BITS_SHIFT + 5 (AS_NO_WRITEBACK_TAGS) = 31 > > mapping->flags is a combination of AS and GFP flags so increasing > __GFP_BITS_SHIFT overflows mapping->flags on 32-bit as gfp_t is an > unsigned int. Got it! Thanks a lot! Best Regards, Huang, Ying -- 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