From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756115AbcH2Trs (ORCPT ); Mon, 29 Aug 2016 15:47:48 -0400 Received: from mga05.intel.com ([192.55.52.43]:60424 "EHLO mga05.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752043AbcH2Trq (ORCPT ); Mon, 29 Aug 2016 15:47:46 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.30,252,1470726000"; d="scan'208";a="1043042466" From: "Huang\, Ying" To: Rik van Riel Cc: Dan Williams , Ross Zwisler , "Huang\, Ying" , Andrew Morton , , , , , , , Hugh Dickins , Shaohua Li , Minchan Kim , Mel Gorman , Tejun Heo , Wu Fengguang Subject: Re: [PATCH] mm: Don't use radix tree writeback tags for pages in swap cache References: <1472153230-14766-1-git-send-email-ying.huang@intel.com> <1472154243.2751.44.camel@redhat.com> Date: Mon, 29 Aug 2016 12:47:45 -0700 In-Reply-To: <1472154243.2751.44.camel@redhat.com> (Rik van Riel's message of "Thu, 25 Aug 2016 15:44:03 -0400") Message-ID: <87shtnxspq.fsf@yhuang-mobile.sh.intel.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.5 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, Rik, Thanks for comments! Rik van Riel writes: > On Thu, 2016-08-25 at 12:27 -0700, Huang, Ying wrote: >> File pages use a set of radix 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. >> >> 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 >>              \          |                \ >>    1207402 ±  7%     +22.3%    1476578 ±  6%  vmstat.swap.so >>    2506952 ±  2%     +28.1%    3212076 ±  7%  vm- >> scalability.throughput >>      10.86 ± 12%     -23.4%       8.31 ± 16%  perf-profile.cycles- >> pp._raw_spin_lock_irq.__add_to_swap_cache.add_to_swap_cache.add_to_sw >> ap.shrink_page_list >>      10.82 ± 13%     -33.1%       7.24 ± 14%  perf-profile.cycles- >> pp._raw_spin_lock_irqsave.__remove_mapping.shrink_page_list.shrink_in >> active_list.shrink_zone_memcg >>      10.36 ± 11%    -100.0%       0.00 ± -1%  perf-profile.cycles- >> pp._raw_spin_lock_irqsave.__test_set_page_writeback.bdev_write_page._ >> _swap_writepage.swap_writepage >>      10.52 ± 12%    -100.0%       0.00 ± -1%  perf-profile.cycles- >> pp._raw_spin_lock_irqsave.test_clear_page_writeback.end_page_writebac >> k.page_endio.pmem_rw_page >> >> Cc: Hugh Dickins >> Cc: Shaohua Li >> Cc: Minchan Kim >> Cc: Rik van Riel >> Cc: Mel Gorman >> Cc: Tejun Heo >> Cc: Wu Fengguang >> Cc: Dave Hansen >> Signed-off-by: "Huang, Ying" >> --- >>  mm/page-writeback.c | 6 ++++-- >>  1 file changed, 4 insertions(+), 2 deletions(-) >> >> diff --git a/mm/page-writeback.c b/mm/page-writeback.c >> index 82e7252..599d2f9 100644 >> --- a/mm/page-writeback.c >> +++ b/mm/page-writeback.c >> @@ -2728,7 +2728,8 @@ int test_clear_page_writeback(struct page >> *page) >>   int ret; >>   >>   lock_page_memcg(page); >> - if (mapping) { >> + /* Pages in swap cache don't use writeback tags */ >> + if (mapping && !PageSwapCache(page)) { > > I wonder if that should be a mapping_uses_tags(mapping) > macro or similar, and a per-mapping flag? > > I suspect there will be another case coming up soon > where we have a page cache radix tree, but no need > for dirty/writeback/... tags. > > That use case would be DAX filesystems, where we do > use a struct page, but that struct page points at > persistent storage, and the tags are not necessary. Asked Dan and Ross for DAX usage of writeback tags. The DAX uses these tags to flush the cache, etc. >>From Dan: " DAX uses them to track PMEM ranges that have taken a write fault so that we can flush/write-back those dirty ranges at fsync()/msync() time. " But I still think that it may be a good idea to use some function or flags for this. Because it is more flexible and readable. Best Regards, Huang, Ying