From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-it0-f71.google.com (mail-it0-f71.google.com [209.85.214.71]) by kanga.kvack.org (Postfix) with ESMTP id E124A83093 for ; Thu, 25 Aug 2016 15:44:28 -0400 (EDT) Received: by mail-it0-f71.google.com with SMTP id e63so4130125ith.2 for ; Thu, 25 Aug 2016 12:44:28 -0700 (PDT) Received: from mx1.redhat.com (mx1.redhat.com. [209.132.183.28]) by mx.google.com with ESMTPS id c84si19963202iod.42.2016.08.25.12.44.21 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 25 Aug 2016 12:44:21 -0700 (PDT) Message-ID: <1472154243.2751.44.camel@redhat.com> Subject: Re: [PATCH] mm: Don't use radix tree writeback tags for pages in swap cache From: Rik van Riel Date: Thu, 25 Aug 2016 15:44:03 -0400 In-Reply-To: <1472153230-14766-1-git-send-email-ying.huang@intel.com> References: <1472153230-14766-1-git-send-email-ying.huang@intel.com> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: owner-linux-mm@kvack.org List-ID: To: "Huang, Ying" , Andrew Morton Cc: 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 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. -- 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