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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.

  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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