From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f69.google.com (mail-pa0-f69.google.com [209.85.220.69]) by kanga.kvack.org (Postfix) with ESMTP id B55496B02CD for ; Mon, 29 Aug 2016 15:47:46 -0400 (EDT) Received: by mail-pa0-f69.google.com with SMTP id ag5so285131431pad.2 for ; Mon, 29 Aug 2016 12:47:46 -0700 (PDT) Received: from mga09.intel.com (mga09.intel.com. [134.134.136.24]) by mx.google.com with ESMTPS id 27si40595546pfn.124.2016.08.29.12.47.45 for (version=TLS1 cipher=AES128-SHA bits=128/128); Mon, 29 Aug 2016 12:47:45 -0700 (PDT) From: "Huang\, Ying" 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> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Sender: owner-linux-mm@kvack.org List-ID: To: Rik van Riel Cc: Dan Williams , Ross Zwisler , "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 , Mel Gorman , Tejun Heo , Wu Fengguang 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.A A But for anonymous pages in the swap cache, >> there is no inode writeback.A A So there is no need to find the >> pages with some writeback tags in the radix tree.A A 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.A A The swap device used is a >> RAM >> simulated PMEM (persistent memory) device.A A The improvement comes >> from >> the reduced contention on the swap cache radix tree lock.A A 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, >> >> baseA A A A A A A A A A A A A base+patch >> ---------------- -------------------------- >> A A A A A A A A A %stddevA A A A A %changeA A A A A A A A A %stddev >> A A A A A A A A A A A A A \A A A A A A A A A A |A A A A A A A A A A A A A A A A \ >> A A A 1207402 A+-A A 7%A A A A A +22.3%A A A A 1476578 A+-A A 6%A A vmstat.swap.so >> A A A 2506952 A+-A A 2%A A A A A +28.1%A A A A 3212076 A+-A A 7%A A vm- >> scalability.throughput >> A A A A A 10.86 A+- 12%A A A A A -23.4%A A A A A A A 8.31 A+- 16%A A perf-profile.cycles- >> pp._raw_spin_lock_irq.__add_to_swap_cache.add_to_swap_cache.add_to_sw >> ap.shrink_page_list >> A A A A A 10.82 A+- 13%A A A A A -33.1%A A A A A A A 7.24 A+- 14%A A perf-profile.cycles- >> pp._raw_spin_lock_irqsave.__remove_mapping.shrink_page_list.shrink_in >> active_list.shrink_zone_memcg >> A A A A A 10.36 A+- 11%A A A A -100.0%A A A A A A A 0.00 A+- -1%A A perf-profile.cycles- >> pp._raw_spin_lock_irqsave.__test_set_page_writeback.bdev_write_page._ >> _swap_writepage.swap_writepage >> A A A A A 10.52 A+- 12%A A A A -100.0%A A A A A A A 0.00 A+- -1%A A 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" >> --- >> A mm/page-writeback.c | 6 ++++-- >> A 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) >> A int ret; >> A >> A 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 -- 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