From: Linus Torvalds <torvalds@linux-foundation.org> To: Dave Chinner <david@fromorbit.com>, Mel Gorman <mgorman@techsingularity.net>, Johannes Weiner <hannes@cmpxchg.org>, Vlastimil Babka <vbabka@suse.cz>, Andrew Morton <akpm@linux-foundation.org> Cc: Bob Peterson <rpeterso@redhat.com>, "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>, "Huang, Ying" <ying.huang@intel.com>, Christoph Hellwig <hch@lst.de>, Wu Fengguang <fengguang.wu@intel.com>, LKP <lkp@01.org>, Tejun Heo <tj@kernel.org>, LKML <linux-kernel@vger.kernel.org> Subject: Re: [LKP] [lkp] [xfs] 68a9f5e700: aim7.jobs-per-min -13.6% regression Date: Mon, 15 Aug 2016 16:48:36 -0700 [thread overview] Message-ID: <CA+55aFwp-Aeu-6j2MfMgEDoUwq+1vThL4nBdMj-p5TqDMA5RrA@mail.gmail.com> (raw) In-Reply-To: <CA+55aFzOAorMxCsv3uyyyhS8c5xteVnZVEm+bGyBjkjWVT5Zag@mail.gmail.com> On Mon, Aug 15, 2016 at 4:20 PM, Linus Torvalds <torvalds@linux-foundation.org> wrote: > > None of this code is all that new, which is annoying. This must have > gone on forever, ... ooh. Wait, I take that back. We actually have some very recent changes that I didn't even think about that went into this very merge window. In particular, I wonder if it's all (or at least partly) due to the new per-node LRU lists. So in shrink_page_list(), when kswapd is encountering a page that is under page writeback due to page reclaim, it does: if (current_is_kswapd() && PageReclaim(page) && test_bit(PGDAT_WRITEBACK, &pgdat->flags)) { nr_immediate++; goto keep_locked; which basically ignores that page and puts it back on the LRU list. But that "is this node under writeback" is new - it now does that per node, and it *used* to do it per zone (so it _used_ to test "is this zone under writeback"). All the mapping pages used to be in the same zone, so I think it effectively single-threaded the kswapd reclaim for one mapping under reclaim writeback. But in your cases, you have multiple nodes... Ok, that's a lot of hand-wavy new-age crystal healing thinking. Really, I haven't looked at it more than "this is one thing that has changed recently, I wonder if it changes the patterns and could explain much higher spin_lock contention on the mapping->tree_lock". I'm adding Mel Gorman and his band of miscreants to the cc, so that they can tell me that I'm full of shit, and completely missed on what that zone->node change actually ends up meaning. Mel? The issue is that Dave Chinner is seeing some nasty spinlock contention on "mapping->tree_lock": > 31.18% [kernel] [k] __pv_queued_spin_lock_slowpath and one of the main paths is this: > - 30.29% kswapd > - 30.23% shrink_node > - 30.07% shrink_node_memcg.isra.75 > - 30.15% shrink_inactive_list > - 29.49% shrink_page_list > - 22.79% __remove_mapping > - 22.27% _raw_spin_lock_irqsave > __pv_queued_spin_lock_slowpath so there's something ridiculously bad going on with a fairly simple benchmark. Dave's benchmark is literally just a "write a new 48GB file in single-page chunks on a 4-node machine". Nothing odd - not rewriting files, not seeking around, no nothing. You can probably recreate it with a silly dd bs=4096 count=$((12*1024*1024)) if=/dev/zero of=bigfile although Dave actually had something rather fancier, I think. Linus
WARNING: multiple messages have this Message-ID (diff)
From: Linus Torvalds <torvalds@linux-foundation.org> To: lkp@lists.01.org Subject: Re: [xfs] 68a9f5e700: aim7.jobs-per-min -13.6% regression Date: Mon, 15 Aug 2016 16:48:36 -0700 [thread overview] Message-ID: <CA+55aFwp-Aeu-6j2MfMgEDoUwq+1vThL4nBdMj-p5TqDMA5RrA@mail.gmail.com> (raw) In-Reply-To: <CA+55aFzOAorMxCsv3uyyyhS8c5xteVnZVEm+bGyBjkjWVT5Zag@mail.gmail.com> [-- Attachment #1: Type: text/plain, Size: 2756 bytes --] On Mon, Aug 15, 2016 at 4:20 PM, Linus Torvalds <torvalds@linux-foundation.org> wrote: > > None of this code is all that new, which is annoying. This must have > gone on forever, ... ooh. Wait, I take that back. We actually have some very recent changes that I didn't even think about that went into this very merge window. In particular, I wonder if it's all (or at least partly) due to the new per-node LRU lists. So in shrink_page_list(), when kswapd is encountering a page that is under page writeback due to page reclaim, it does: if (current_is_kswapd() && PageReclaim(page) && test_bit(PGDAT_WRITEBACK, &pgdat->flags)) { nr_immediate++; goto keep_locked; which basically ignores that page and puts it back on the LRU list. But that "is this node under writeback" is new - it now does that per node, and it *used* to do it per zone (so it _used_ to test "is this zone under writeback"). All the mapping pages used to be in the same zone, so I think it effectively single-threaded the kswapd reclaim for one mapping under reclaim writeback. But in your cases, you have multiple nodes... Ok, that's a lot of hand-wavy new-age crystal healing thinking. Really, I haven't looked at it more than "this is one thing that has changed recently, I wonder if it changes the patterns and could explain much higher spin_lock contention on the mapping->tree_lock". I'm adding Mel Gorman and his band of miscreants to the cc, so that they can tell me that I'm full of shit, and completely missed on what that zone->node change actually ends up meaning. Mel? The issue is that Dave Chinner is seeing some nasty spinlock contention on "mapping->tree_lock": > 31.18% [kernel] [k] __pv_queued_spin_lock_slowpath and one of the main paths is this: > - 30.29% kswapd > - 30.23% shrink_node > - 30.07% shrink_node_memcg.isra.75 > - 30.15% shrink_inactive_list > - 29.49% shrink_page_list > - 22.79% __remove_mapping > - 22.27% _raw_spin_lock_irqsave > __pv_queued_spin_lock_slowpath so there's something ridiculously bad going on with a fairly simple benchmark. Dave's benchmark is literally just a "write a new 48GB file in single-page chunks on a 4-node machine". Nothing odd - not rewriting files, not seeking around, no nothing. You can probably recreate it with a silly dd bs=4096 count=$((12*1024*1024)) if=/dev/zero of=bigfile although Dave actually had something rather fancier, I think. Linus
next prev parent reply other threads:[~2016-08-15 23:48 UTC|newest] Thread overview: 219+ messages / expand[flat|nested] mbox.gz Atom feed top 2016-08-09 14:33 [lkp] [xfs] 68a9f5e700: aim7.jobs-per-min -13.6% regression kernel test robot 2016-08-09 14:33 ` kernel test robot 2016-08-10 18:24 ` [lkp] " Linus Torvalds 2016-08-10 18:24 ` Linus Torvalds 2016-08-10 23:08 ` [lkp] " Dave Chinner 2016-08-10 23:08 ` Dave Chinner 2016-08-10 23:51 ` [lkp] " Linus Torvalds 2016-08-10 23:51 ` Linus Torvalds 2016-08-10 23:58 ` [LKP] [lkp] " Huang, Ying 2016-08-10 23:58 ` Huang, Ying 2016-08-11 0:11 ` [LKP] [lkp] " Huang, Ying 2016-08-11 0:11 ` Huang, Ying 2016-08-11 0:23 ` [LKP] [lkp] " Linus Torvalds 2016-08-11 0:23 ` Linus Torvalds 2016-08-11 0:33 ` [LKP] [lkp] " Huang, Ying 2016-08-11 0:33 ` Huang, Ying 2016-08-11 1:00 ` [LKP] [lkp] " Linus Torvalds 2016-08-11 1:00 ` Linus Torvalds 2016-08-11 4:46 ` [LKP] [lkp] " Dave Chinner 2016-08-11 4:46 ` Dave Chinner 2016-08-15 17:22 ` [LKP] [lkp] " Huang, Ying 2016-08-15 17:22 ` Huang, Ying 2016-08-16 0:08 ` [LKP] [lkp] " Dave Chinner 2016-08-16 0:08 ` Dave Chinner 2016-08-11 15:57 ` [LKP] [lkp] " Christoph Hellwig 2016-08-11 15:57 ` Christoph Hellwig 2016-08-11 16:55 ` [LKP] [lkp] " Linus Torvalds 2016-08-11 16:55 ` Linus Torvalds 2016-08-11 17:51 ` [LKP] [lkp] " Huang, Ying 2016-08-11 17:51 ` Huang, Ying 2016-08-11 19:51 ` [LKP] [lkp] " Linus Torvalds 2016-08-11 19:51 ` Linus Torvalds 2016-08-11 20:00 ` [LKP] [lkp] " Christoph Hellwig 2016-08-11 20:00 ` Christoph Hellwig 2016-08-11 20:35 ` [LKP] [lkp] " Linus Torvalds 2016-08-11 20:35 ` Linus Torvalds 2016-08-11 22:16 ` [LKP] [lkp] " Al Viro 2016-08-11 22:16 ` Al Viro 2016-08-11 22:30 ` [LKP] [lkp] " Linus Torvalds 2016-08-11 22:30 ` Linus Torvalds 2016-08-11 21:16 ` [LKP] [lkp] " Huang, Ying 2016-08-11 21:16 ` Huang, Ying 2016-08-11 21:40 ` [LKP] [lkp] " Linus Torvalds 2016-08-11 21:40 ` Linus Torvalds 2016-08-11 22:08 ` [LKP] [lkp] " Christoph Hellwig 2016-08-11 22:08 ` Christoph Hellwig 2016-08-12 0:54 ` [LKP] [lkp] " Dave Chinner 2016-08-12 0:54 ` Dave Chinner 2016-08-12 2:23 ` [LKP] [lkp] " Dave Chinner 2016-08-12 2:23 ` Dave Chinner 2016-08-12 2:32 ` [LKP] [lkp] " Linus Torvalds 2016-08-12 2:32 ` Linus Torvalds 2016-08-12 2:52 ` [LKP] [lkp] " Christoph Hellwig 2016-08-12 2:52 ` Christoph Hellwig 2016-08-12 3:20 ` [LKP] [lkp] " Linus Torvalds 2016-08-12 3:20 ` Linus Torvalds 2016-08-12 4:16 ` [LKP] [lkp] " Dave Chinner 2016-08-12 4:16 ` Dave Chinner 2016-08-12 5:02 ` [LKP] [lkp] " Linus Torvalds 2016-08-12 5:02 ` Linus Torvalds 2016-08-12 6:04 ` [LKP] [lkp] " Dave Chinner 2016-08-12 6:04 ` Dave Chinner 2016-08-12 6:29 ` [LKP] [lkp] " Ye Xiaolong 2016-08-12 6:29 ` Ye Xiaolong 2016-08-12 8:51 ` [LKP] [lkp] " Ye Xiaolong 2016-08-12 8:51 ` Ye Xiaolong 2016-08-12 10:02 ` [LKP] [lkp] " Dave Chinner 2016-08-12 10:02 ` Dave Chinner 2016-08-12 10:43 ` Fengguang Wu 2016-08-12 10:43 ` Fengguang Wu 2016-08-13 0:30 ` [LKP] [lkp] " Christoph Hellwig 2016-08-13 0:30 ` Christoph Hellwig 2016-08-13 21:48 ` [LKP] [lkp] " Christoph Hellwig 2016-08-13 21:48 ` Christoph Hellwig 2016-08-13 22:07 ` [LKP] [lkp] " Fengguang Wu 2016-08-13 22:07 ` Fengguang Wu 2016-08-13 22:15 ` [LKP] [lkp] " Christoph Hellwig 2016-08-13 22:15 ` Christoph Hellwig 2016-08-13 22:51 ` [LKP] [lkp] " Fengguang Wu 2016-08-13 22:51 ` Fengguang Wu 2016-08-14 14:50 ` [LKP] [lkp] " Fengguang Wu 2016-08-14 14:50 ` Fengguang Wu 2016-08-14 16:17 ` [LKP] [lkp] " Christoph Hellwig 2016-08-14 16:17 ` Christoph Hellwig 2016-08-14 23:46 ` [LKP] [lkp] " Dave Chinner 2016-08-14 23:46 ` Dave Chinner 2016-08-14 23:57 ` [LKP] [lkp] " Fengguang Wu 2016-08-14 23:57 ` Fengguang Wu 2016-08-15 14:14 ` [LKP] [lkp] " Fengguang Wu 2016-08-15 14:14 ` Fengguang Wu 2016-08-15 21:22 ` [LKP] [lkp] " Dave Chinner 2016-08-15 21:22 ` Dave Chinner 2016-08-16 12:20 ` [LKP] [lkp] " Fengguang Wu 2016-08-16 12:20 ` Fengguang Wu 2016-08-15 20:30 ` [LKP] [lkp] " Huang, Ying 2016-08-15 20:30 ` Huang, Ying 2016-08-22 22:09 ` [LKP] [lkp] " Huang, Ying 2016-08-22 22:09 ` Huang, Ying 2016-09-26 6:25 ` [LKP] [lkp] " Huang, Ying 2016-09-26 6:25 ` Huang, Ying 2016-09-26 14:55 ` [LKP] [lkp] " Christoph Hellwig 2016-09-26 14:55 ` Christoph Hellwig 2016-09-27 0:52 ` [LKP] [lkp] " Huang, Ying 2016-09-27 0:52 ` Huang, Ying 2016-08-16 13:25 ` [LKP] [lkp] " Fengguang Wu 2016-08-16 13:25 ` Fengguang Wu 2016-08-13 23:32 ` [LKP] [lkp] " Dave Chinner 2016-08-13 23:32 ` Dave Chinner 2016-08-12 2:27 ` [LKP] [lkp] " Linus Torvalds 2016-08-12 2:27 ` Linus Torvalds 2016-08-12 3:56 ` [LKP] [lkp] " Dave Chinner 2016-08-12 3:56 ` Dave Chinner 2016-08-12 18:03 ` [LKP] [lkp] " Linus Torvalds 2016-08-12 18:03 ` Linus Torvalds 2016-08-13 23:58 ` [LKP] [lkp] " Fengguang Wu 2016-08-13 23:58 ` Fengguang Wu 2016-08-15 0:48 ` [LKP] [lkp] " Dave Chinner 2016-08-15 0:48 ` Dave Chinner 2016-08-15 1:37 ` [LKP] [lkp] " Linus Torvalds 2016-08-15 1:37 ` Linus Torvalds 2016-08-15 2:28 ` [LKP] [lkp] " Dave Chinner 2016-08-15 2:28 ` Dave Chinner 2016-08-15 2:53 ` [LKP] [lkp] " Linus Torvalds 2016-08-15 2:53 ` Linus Torvalds 2016-08-15 5:00 ` [LKP] [lkp] " Dave Chinner 2016-08-15 5:00 ` Dave Chinner [not found] ` <CA+55aFwva2Xffai+Eqv1Jn_NGryk3YJ2i5JoHOQnbQv6qVPAsw@mail.gmail.com> [not found] ` <CA+55aFy14nUnJQ_GdF=j8Fa9xiH70c6fY2G3q5HQ01+8z1z3qQ@mail.gmail.com> 2016-08-15 5:12 ` Linus Torvalds 2016-08-15 22:22 ` [LKP] [lkp] " Dave Chinner 2016-08-15 22:22 ` Dave Chinner 2016-08-15 22:42 ` [LKP] [lkp] " Dave Chinner 2016-08-15 22:42 ` Dave Chinner 2016-08-15 23:20 ` [LKP] [lkp] " Linus Torvalds 2016-08-15 23:20 ` Linus Torvalds 2016-08-15 23:48 ` Linus Torvalds [this message] 2016-08-15 23:48 ` Linus Torvalds 2016-08-16 0:44 ` [LKP] [lkp] " Dave Chinner 2016-08-16 0:44 ` Dave Chinner 2016-08-16 15:05 ` [LKP] [lkp] " Mel Gorman 2016-08-16 15:05 ` Mel Gorman 2016-08-16 17:47 ` [LKP] [lkp] " Linus Torvalds 2016-08-16 17:47 ` Linus Torvalds 2016-08-17 15:48 ` [LKP] [lkp] " Michal Hocko 2016-08-17 15:48 ` Michal Hocko 2016-08-17 16:42 ` [LKP] [lkp] " Michal Hocko 2016-08-17 16:42 ` Michal Hocko 2016-08-17 15:49 ` [LKP] [lkp] " Mel Gorman 2016-08-17 15:49 ` Mel Gorman 2016-08-18 0:45 ` [LKP] [lkp] " Mel Gorman 2016-08-18 0:45 ` Mel Gorman 2016-08-18 7:11 ` [LKP] [lkp] " Dave Chinner 2016-08-18 7:11 ` Dave Chinner 2016-08-18 13:24 ` [LKP] [lkp] " Mel Gorman 2016-08-18 13:24 ` Mel Gorman 2016-08-18 17:55 ` [LKP] [lkp] " Linus Torvalds 2016-08-18 17:55 ` Linus Torvalds 2016-08-18 21:19 ` [LKP] [lkp] " Dave Chinner 2016-08-18 21:19 ` Dave Chinner 2016-08-18 22:25 ` [LKP] [lkp] " Linus Torvalds 2016-08-18 22:25 ` Linus Torvalds 2016-08-19 9:00 ` [LKP] [lkp] " Michal Hocko 2016-08-19 9:00 ` Michal Hocko 2016-08-19 10:49 ` [LKP] [lkp] " Mel Gorman 2016-08-19 10:49 ` Mel Gorman 2016-08-19 23:48 ` [LKP] [lkp] " Dave Chinner 2016-08-19 23:48 ` Dave Chinner 2016-08-20 1:08 ` [LKP] [lkp] " Linus Torvalds 2016-08-20 1:08 ` Linus Torvalds 2016-08-20 12:16 ` [LKP] [lkp] " Mel Gorman 2016-08-20 12:16 ` Mel Gorman 2016-08-19 15:08 ` [LKP] [lkp] " Mel Gorman 2016-08-19 15:08 ` Mel Gorman 2016-09-01 23:32 ` [LKP] [lkp] " Dave Chinner 2016-09-01 23:32 ` Dave Chinner 2016-09-06 15:37 ` [LKP] [lkp] " Mel Gorman 2016-09-06 15:37 ` Mel Gorman 2016-09-06 15:52 ` [LKP] [lkp] " Huang, Ying 2016-09-06 15:52 ` Huang, Ying 2016-08-24 15:40 ` [LKP] [lkp] " Huang, Ying 2016-08-24 15:40 ` Huang, Ying 2016-08-25 9:37 ` [LKP] [lkp] " Mel Gorman 2016-08-25 9:37 ` Mel Gorman 2016-08-18 2:44 ` [LKP] [lkp] " Dave Chinner 2016-08-18 2:44 ` Dave Chinner 2016-08-16 0:15 ` [LKP] [lkp] " Linus Torvalds 2016-08-16 0:15 ` Linus Torvalds 2016-08-16 0:38 ` [LKP] [lkp] " Dave Chinner 2016-08-16 0:38 ` Dave Chinner 2016-08-16 0:50 ` [LKP] [lkp] " Linus Torvalds 2016-08-16 0:50 ` Linus Torvalds 2016-08-16 0:19 ` [LKP] [lkp] " Dave Chinner 2016-08-16 0:19 ` Dave Chinner 2016-08-16 1:51 ` [LKP] [lkp] " Linus Torvalds 2016-08-16 1:51 ` Linus Torvalds 2016-08-16 22:02 ` [LKP] [lkp] " Dave Chinner 2016-08-16 22:02 ` Dave Chinner 2016-08-16 23:23 ` [LKP] [lkp] " Linus Torvalds 2016-08-16 23:23 ` Linus Torvalds 2016-08-15 23:01 ` [LKP] [lkp] " Linus Torvalds 2016-08-15 23:01 ` Linus Torvalds 2016-08-16 0:17 ` [LKP] [lkp] " Dave Chinner 2016-08-16 0:17 ` Dave Chinner 2016-08-16 0:45 ` [LKP] [lkp] " Linus Torvalds 2016-08-16 0:45 ` Linus Torvalds 2016-08-15 5:03 ` [LKP] [lkp] " Ingo Molnar 2016-08-15 5:03 ` Ingo Molnar 2016-08-17 16:24 ` [LKP] [lkp] " Peter Zijlstra 2016-08-17 16:24 ` Peter Zijlstra 2016-08-15 12:58 ` [LKP] [lkp] " Fengguang Wu 2016-08-15 12:58 ` Fengguang Wu 2016-08-11 1:16 ` [LKP] [lkp] " Dave Chinner 2016-08-11 1:16 ` Dave Chinner 2016-08-11 1:32 ` [LKP] [lkp] " Dave Chinner 2016-08-11 1:32 ` Dave Chinner 2016-08-11 2:36 ` [LKP] [lkp] " Ye Xiaolong 2016-08-11 2:36 ` Ye Xiaolong 2016-08-11 3:05 ` [LKP] [lkp] " Dave Chinner 2016-08-11 3:05 ` Dave Chinner 2016-08-12 1:26 ` [LKP] [lkp] " Dave Chinner 2016-08-12 1:26 ` Dave Chinner
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