From: Yu Zhao <yuzhao@google.com>
To: "Huang, Ying" <ying.huang@intel.com>
Cc: Dave Hansen <dave.hansen@intel.com>,
Linux-MM <linux-mm@kvack.org>,
Alex Shi <alex.shi@linux.alibaba.com>,
Andrew Morton <akpm@linux-foundation.org>,
Dave Hansen <dave.hansen@linux.intel.com>,
Hillf Danton <hdanton@sina.com>,
Johannes Weiner <hannes@cmpxchg.org>,
Joonsoo Kim <iamjoonsoo.kim@lge.com>,
Matthew Wilcox <willy@infradead.org>,
Mel Gorman <mgorman@suse.de>, Michal Hocko <mhocko@suse.com>,
Roman Gushchin <guro@fb.com>, Vlastimil Babka <vbabka@suse.cz>,
Wei Yang <richard.weiyang@linux.alibaba.com>,
Yang Shi <shy828301@gmail.com>,
linux-kernel <linux-kernel@vger.kernel.org>,
Kernel Page Reclaim v2 <page-reclaim@google.com>
Subject: Re: [PATCH v1 00/14] Multigenerational LRU
Date: Tue, 13 Apr 2021 17:00:24 -0600 [thread overview]
Message-ID: <CAOUHufbTCwPP5KtOMmrYPJ-4RpHWJHJQx7k4S95_vQCHm+zXtg@mail.gmail.com> (raw)
In-Reply-To: <87zgy2ubtd.fsf@yhuang6-desk1.ccr.corp.intel.com>
On Mon, Apr 12, 2021 at 9:02 PM Huang, Ying <ying.huang@intel.com> wrote:
>
> Yu Zhao <yuzhao@google.com> writes:
>
> > On Tue, Mar 16, 2021 at 02:14:43PM -0700, Dave Hansen wrote:
> >> On 3/16/21 1:30 PM, Yu Zhao wrote:
> >> > On Tue, Mar 16, 2021 at 07:50:23AM -0700, Dave Hansen wrote:
> >> >> I think it would also be very worthwhile to include some research in
> >> >> this series about why the kernel moved away from page table scanning.
> >> >> What has changed? Are the workloads we were concerned about way back
> >> >> then not around any more? Has faster I/O or larger memory sizes with a
> >> >> stagnating page size changed something?
> >> >
> >> > Sure. Hugh also suggested this too but I personally found that ancient
> >> > pre-2.4 history too irrelevant (and uninteresting) to the modern age
> >> > and decided to spare audience of the boredom.
> >>
> >> IIRC, rmap chains showed up in the 2.5 era and the VM was quite bumpy
> >> until anon_vmas came around, which was early-ish in the 2.6 era.
> >>
> >> But, either way, I think there is a sufficient population of nostalgic
> >> crusty old folks around to warrant a bit of a history lesson. We'll
> >> enjoy the trip down memory lane, fondly remembering the old days in
> >> Ottawa...
> >>
> >> >>> nr_vmscan_write 24900719
> >> >>> nr_vmscan_immediate_reclaim 115535
> >> >>> pgscan_kswapd 320831544
> >> >>> pgscan_direct 23396383
> >> >>> pgscan_direct_throttle 0
> >> >>> pgscan_anon 127491077
> >> >>> pgscan_file 216736850
> >> >>> slabs_scanned 400469680
> >> >>> compact_migrate_scanned 1092813949
> >> >>> compact_free_scanned 4919523035
> >> >>> compact_daemon_migrate_scanned 2372223
> >> >>> compact_daemon_free_scanned 20989310
> >> >>> unevictable_pgs_scanned 307388545
> >> >
> >> > 10G swap + 8G anon rss + 6G file rss, hmm... an interesting workload.
> >> > The file rss does seem a bit high to me, my wild speculation is there
> >> > have been git/make activities in addition to a VM?
> >>
> >> I wish I was doing more git/make activities. It's been an annoying
> >> amount of email and web browsers for 12 days. If anything, I'd suspect
> >> that Thunderbird is at fault for keeping a bunch of mail in the page
> >> cache. There are a couple of VM's running though.
> >
> > Hi Dave,
> >
> > Sorry for the late reply. Here is the benchmark result from the worst
> > case scenario.
> >
> > As you suggested, we create a lot of processes sharing one large
> > sparse shmem, and they access the shmem at random 2MB-aligned offsets.
> > So there will be at most one valid PTE entry per PTE table, hence the
> > worst case scenario for the multigenerational LRU, since it is based
> > on page table scanning.
> >
> > TL;DR: the multigenerational LRU did not perform worse than the rmap.
> >
> > My test configurations:
> >
> > The size of the shmem: 256GB
> > The number of processes: 450
> > Total memory size: 200GB
> > The number of CPUs: 64
> > The number of nodes: 2
> >
> > There is no clear winner in the background reclaim path (kswapd).
> >
> > kswapd (5.12.0-rc6):
> > 43.99% kswapd1 page_vma_mapped_walk
> > 34.86% kswapd0 page_vma_mapped_walk
> > 2.43% kswapd0 count_shadow_nodes
> > 1.17% kswapd1 page_referenced_one
> > 1.15% kswapd0 _find_next_bit.constprop.0
> > 0.95% kswapd0 page_referenced_one
> > 0.87% kswapd1 try_to_unmap_one
> > 0.75% kswapd0 cpumask_next
> > 0.67% kswapd0 shrink_slab
> > 0.66% kswapd0 down_read_trylock
> >
> > kswapd (the multigenerational LRU):
> > 33.39% kswapd0 walk_pud_range
> > 10.93% kswapd1 walk_pud_range
> > 9.36% kswapd0 page_vma_mapped_walk
> > 7.15% kswapd1 page_vma_mapped_walk
> > 3.83% kswapd0 count_shadow_nodes
> > 2.60% kswapd1 shrink_slab
> > 2.47% kswapd1 down_read_trylock
> > 2.03% kswapd0 _raw_spin_lock
> > 1.87% kswapd0 shrink_slab
> > 1.67% kswapd1 count_shadow_nodes
> >
> > The multigenerational LRU is somewhat winning in the direct reclaim
> > path (sparse is the test binary name):
> >
> > The test process context (5.12.0-rc6):
> > 65.02% sparse page_vma_mapped_walk
> > 5.49% sparse page_counter_try_charge
> > 3.60% sparse propagate_protected_usage
> > 2.31% sparse page_counter_uncharge
> > 2.06% sparse count_shadow_nodes
> > 1.81% sparse native_queued_spin_lock_slowpath
> > 1.79% sparse down_read_trylock
> > 1.67% sparse page_referenced_one
> > 1.42% sparse shrink_slab
> > 0.87% sparse try_to_unmap_one
> >
> > CPU % (direct reclaim vs the rest): 71% vs 29%
> > # grep oom_kill /proc/vmstat
> > oom_kill 81
> >
> > The test process context (the multigenerational LRU):
> > 33.12% sparse page_vma_mapped_walk
> > 10.70% sparse walk_pud_range
> > 9.64% sparse page_counter_try_charge
> > 6.63% sparse propagate_protected_usage
> > 4.43% sparse native_queued_spin_lock_slowpath
> > 3.85% sparse page_counter_uncharge
> > 3.71% sparse irqentry_exit_to_user_mode
> > 2.16% sparse _raw_spin_lock
> > 1.83% sparse unmap_page_range
> > 1.82% sparse shrink_slab
> >
> > CPU % (direct reclaim vs the rest): 47% vs 53%
> > # grep oom_kill /proc/vmstat
> > oom_kill 80
> >
> > I also compared other numbers from /proc/vmstat. They do not provide
> > any additional insight than the profiles, so I will just omit them
> > here.
> >
> > The following optimizations and the stats measuring their efficacies
> > explain why the multigenerational LRU did not perform worse:
> >
> > Optimization 1: take advantage of the scheduling information.
> > # of active processes 270
> > # of inactive processes 105
> >
> > Optimization 2: take the advantage of the accessed bit on non-leaf
> > PMD entries.
> > # of old non-leaf PMD entries 30523335
> > # of young non-leaf PMD entries 1358400
> >
> > These stats are not currently included. But I will add them to the
> > debugfs interface in the next version coming soon. And I will also add
> > another optimization for Android. It reduces zigzags when there are
> > many single-page VMAs, i.e., not returning to the PGD table for each
> > of such VMAs. Just a heads-up.
> >
> > The rmap, on the other hand, had to
> > 1) lock each (shmem) page it scans
> > 2) go through five levels of page tables for each page, even though
> > some of them have the same LCAs
> > during the test. The second part is worse given that I have 5 levels
> > of page tables configured.
> >
> > Any additional benchmarks you would suggest? Thanks.
>
> Hi, Yu,
>
> Thanks for your data.
>
> In addition to the data your measured above, is it possible for you to
> measure some raw data? For example, how many CPU cycles does it take to
> scan all pages in the system? For the page table scanning, the page
> tables of all processes will be scanned. For the rmap scanning, all
> pages in LRU will be scanned. And we can do that with difference
> parameters, for example, shared vs. non-shared, sparse vs. dense. Then
> we can get an idea about how fast the page table scanning can be.
SGTM. I'll get back to you later.
next prev parent reply other threads:[~2021-04-13 23:00 UTC|newest]
Thread overview: 55+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-13 7:57 [PATCH v1 00/14] Multigenerational LRU Yu Zhao
2021-03-13 7:57 ` [PATCH v1 01/14] include/linux/memcontrol.h: do not warn in page_memcg_rcu() if !CONFIG_MEMCG Yu Zhao
2021-03-13 15:09 ` Matthew Wilcox
2021-03-14 7:45 ` Yu Zhao
2021-03-13 7:57 ` [PATCH v1 02/14] include/linux/nodemask.h: define next_memory_node() if !CONFIG_NUMA Yu Zhao
2021-03-13 7:57 ` [PATCH v1 03/14] include/linux/huge_mm.h: define is_huge_zero_pmd() if !CONFIG_TRANSPARENT_HUGEPAGE Yu Zhao
2021-03-13 7:57 ` [PATCH v1 04/14] include/linux/cgroup.h: export cgroup_mutex Yu Zhao
2021-03-13 7:57 ` [PATCH v1 05/14] mm/swap.c: export activate_page() Yu Zhao
2021-03-13 7:57 ` [PATCH v1 06/14] mm, x86: support the access bit on non-leaf PMD entries Yu Zhao
2021-03-14 22:12 ` Zi Yan
2021-03-14 22:51 ` Matthew Wilcox
2021-03-15 0:03 ` Yu Zhao
2021-03-15 0:27 ` Zi Yan
2021-03-15 1:04 ` Yu Zhao
2021-03-14 23:22 ` Dave Hansen
2021-03-15 3:16 ` Yu Zhao
2021-03-13 7:57 ` [PATCH v1 07/14] mm/pagewalk.c: add pud_entry_post() for post-order traversals Yu Zhao
2021-03-13 7:57 ` [PATCH v1 08/14] mm/vmscan.c: refactor shrink_node() Yu Zhao
2021-03-13 7:57 ` [PATCH v1 09/14] mm: multigenerational lru: mm_struct list Yu Zhao
2021-03-15 19:40 ` Rik van Riel
2021-03-16 2:07 ` Huang, Ying
2021-03-16 3:57 ` Yu Zhao
2021-03-16 6:44 ` Huang, Ying
2021-03-16 7:56 ` Yu Zhao
2021-03-17 3:37 ` Huang, Ying
2021-03-17 10:46 ` Yu Zhao
2021-03-22 3:13 ` Huang, Ying
2021-03-22 8:08 ` Yu Zhao
2021-03-24 6:58 ` Huang, Ying
2021-04-10 18:48 ` Yu Zhao
2021-04-13 3:06 ` Huang, Ying
2021-03-13 7:57 ` [PATCH v1 10/14] mm: multigenerational lru: core Yu Zhao
2021-03-15 2:02 ` Andi Kleen
2021-03-15 3:37 ` Yu Zhao
2021-03-13 7:57 ` [PATCH v1 11/14] mm: multigenerational lru: page activation Yu Zhao
2021-03-16 16:34 ` Matthew Wilcox
2021-03-16 21:29 ` Yu Zhao
2021-03-13 7:57 ` [PATCH v1 12/14] mm: multigenerational lru: user space interface Yu Zhao
2021-03-13 7:57 ` [PATCH v1 13/14] mm: multigenerational lru: Kconfig Yu Zhao
2021-03-13 7:57 ` [PATCH v1 14/14] mm: multigenerational lru: documentation Yu Zhao
2021-03-19 9:31 ` Alex Shi
2021-03-22 6:09 ` Yu Zhao
2021-03-14 22:48 ` [PATCH v1 00/14] Multigenerational LRU Zi Yan
2021-03-15 0:52 ` Yu Zhao
[not found] ` <20210315011350.3648-1-hdanton@sina.com>
2021-03-15 6:49 ` Yu Zhao
2021-03-15 18:00 ` Dave Hansen
2021-03-16 2:24 ` Yu Zhao
2021-03-16 14:50 ` Dave Hansen
2021-03-16 20:30 ` Yu Zhao
2021-03-16 21:14 ` Dave Hansen
2021-04-10 9:21 ` Yu Zhao
2021-04-13 3:02 ` Huang, Ying
2021-04-13 23:00 ` Yu Zhao [this message]
2021-03-15 18:38 ` Yang Shi
2021-03-16 3:38 ` Yu Zhao
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