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Date: Mon, 21 Mar 2022 18:31:36 +0530
From: "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>
To: Yu Zhao <yuzhao@...gle.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Andi Kleen <ak@...ux.intel.com>,
Catalin Marinas <catalin.marinas@....com>,
Dave Hansen <dave.hansen@...ux.intel.com>,
Hillf Danton <hdanton@...a.com>, Jens Axboe <axboe@...nel.dk>,
Jesse Barnes <jsbarnes@...gle.com>,
Johannes Weiner <hannes@...xchg.org>,
Jonathan Corbet <corbet@....net>,
Matthew Wilcox <willy@...radead.org>,
Mel Gorman <mgorman@...e.de>,
Michael Larabel <Michael@...haellarabel.com>,
Michal Hocko <mhocko@...nel.org>,
Mike Rapoport <rppt@...nel.org>,
Rik van Riel <riel@...riel.com>,
Vlastimil Babka <vbabka@...e.cz>,
Will Deacon <will@...nel.org>,
Ying Huang <ying.huang@...el.com>,
linux-arm-kernel@...ts.infradead.org, linux-doc@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-mm@...ck.org,
page-reclaim@...gle.com, x86@...nel.org,
Yu Zhao <yuzhao@...gle.com>, Brian Geffon <bgeffon@...gle.com>,
Jan Alexander Steffens <heftig@...hlinux.org>,
Oleksandr Natalenko <oleksandr@...alenko.name>,
Steven Barrett <steven@...uorix.net>,
Suleiman Souhlal <suleiman@...gle.com>,
Daniel Byrne <djbyrne@....edu>,
Donald Carr <d@...os-reins.com>,
Holger Hoffstätte
<holger@...lied-asynchrony.com>,
Konstantin Kharlamov <Hi-Angel@...dex.ru>,
Shuang Zhai <szhai2@...rochester.edu>,
Sofia Trinh <sofia.trinh@....works>,
Vaibhav Jain <vaibhav@...ux.ibm.com>
Subject: Re: [PATCH v9 06/14] mm: multi-gen LRU: minimal implementation
Yu Zhao <yuzhao@...gle.com> writes:
> To avoid confusion, the terms "promotion" and "demotion" will be
> applied to the multi-gen LRU, as a new convention; the terms
> "activation" and "deactivation" will be applied to the active/inactive
> LRU, as usual.
>
> The aging produces young generations. Given an lruvec, it increments
> max_seq when max_seq-min_seq+1 approaches MIN_NR_GENS. The aging
> promotes hot pages to the youngest generation when it finds them
> accessed through page tables; the demotion of cold pages happens
> consequently when it increments max_seq. The aging has the complexity
> O(nr_hot_pages), since it is only interested in hot pages. Promotion
> in the aging path does not require any LRU list operations, only the
> updates of the gen counter and lrugen->nr_pages[]; demotion, unless as
> the result of the increment of max_seq, requires LRU list operations,
> e.g., lru_deactivate_fn().
>
> The eviction consumes old generations. Given an lruvec, it increments
> min_seq when the lists indexed by min_seq%MAX_NR_GENS become empty. A
> feedback loop modeled after the PID controller monitors refaults over
> anon and file types and decides which type to evict when both types
> are available from the same generation.
>
> Each generation is divided into multiple tiers. Tiers represent
> different ranges of numbers of accesses through file descriptors. A
> page accessed N times through file descriptors is in tier
> order_base_2(N). Tiers do not have dedicated lrugen->lists[], only
> bits in folio->flags. In contrast to moving across generations, which
> requires the LRU lock, moving across tiers only involves operations on
> folio->flags. The feedback loop also monitors refaults over all tiers
> and decides when to protect pages in which tiers (N>1), using the
> first tier (N=0,1) as a baseline. The first tier contains single-use
> unmapped clean pages, which are most likely the best choices. The
> eviction moves a page to the next generation, i.e., min_seq+1, if the
> feedback loop decides so. This approach has the following advantages:
> 1. It removes the cost of activation in the buffered access path by
> inferring whether pages accessed multiple times through file
> descriptors are statistically hot and thus worth protecting in the
> eviction path.
> 2. It takes pages accessed through page tables into account and avoids
> overprotecting pages accessed multiple times through file
> descriptors. (Pages accessed through page tables are in the first
> tier, since N=0.)
> 3. More tiers provide better protection for pages accessed more than
> twice through file descriptors, when under heavy buffered I/O
> workloads.
>
> Server benchmark results:
> Single workload:
> fio (buffered I/O): +[47, 49]%
> IOPS BW
> 5.17-rc2: 2242k 8759MiB/s
> patch1-5: 3321k 12.7GiB/s
>
> Single workload:
> memcached (anon): +[101, 105]%
> Ops/sec KB/sec
> 5.17-rc2: 476771.79 18544.31
> patch1-5: 972526.07 37826.95
>
> Configurations:
> CPU: two Xeon 6154
> Mem: total 256G
>
> Node 1 was only used as a ram disk to reduce the variance in the
> results.
>
> patch drivers/block/brd.c <<EOF
> 99,100c99,100
> < gfp_flags = GFP_NOIO | __GFP_ZERO | __GFP_HIGHMEM;
> < page = alloc_page(gfp_flags);
> ---
> > gfp_flags = GFP_NOIO | __GFP_ZERO | __GFP_HIGHMEM | __GFP_THISNODE;
> > page = alloc_pages_node(1, gfp_flags, 0);
> EOF
>
> cat >>/etc/systemd/system.conf <<EOF
> CPUAffinity=numa
> NUMAPolicy=bind
> NUMAMask=0
> EOF
>
> cat >>/etc/memcached.conf <<EOF
> -m 184320
> -s /var/run/memcached/memcached.sock
> -a 0766
> -t 36
> -B binary
> EOF
>
> cat fio.sh
> modprobe brd rd_nr=1 rd_size=113246208
> mkfs.ext4 /dev/ram0
> mount -t ext4 /dev/ram0 /mnt
>
> mkdir /sys/fs/cgroup/user.slice/test
> echo 38654705664 >/sys/fs/cgroup/user.slice/test/memory.max
> echo $$ >/sys/fs/cgroup/user.slice/test/cgroup.procs
> fio -name=mglru --numjobs=72 --directory=/mnt --size=1408m \
> --buffered=1 --ioengine=io_uring --iodepth=128 \
> --iodepth_batch_submit=32 --iodepth_batch_complete=32 \
> --rw=randread --random_distribution=random --norandommap \
> --time_based --ramp_time=10m --runtime=5m --group_reporting
>
> cat memcached.sh
> modprobe brd rd_nr=1 rd_size=113246208
> swapoff -a
> mkswap /dev/ram0
> swapon /dev/ram0
>
> memtier_benchmark -S /var/run/memcached/memcached.sock \
> -P memcache_binary -n allkeys --key-minimum=1 \
> --key-maximum=65000000 --key-pattern=P:P -c 1 -t 36 \
> --ratio 1:0 --pipeline 8 -d 2000
>
> memtier_benchmark -S /var/run/memcached/memcached.sock \
> -P memcache_binary -n allkeys --key-minimum=1 \
> --key-maximum=65000000 --key-pattern=R:R -c 1 -t 36 \
> --ratio 0:1 --pipeline 8 --randomize --distinct-client-seed
>
> Client benchmark results:
> kswapd profiles:
> 5.17-rc2
> 38.05% page_vma_mapped_walk
> 20.86% lzo1x_1_do_compress (real work)
> 6.16% do_raw_spin_lock
> 4.61% _raw_spin_unlock_irq
> 2.20% vma_interval_tree_iter_next
> 2.19% vma_interval_tree_subtree_search
> 2.15% page_referenced_one
> 1.93% anon_vma_interval_tree_iter_first
> 1.65% ptep_clear_flush
> 1.00% __zram_bvec_write
>
> patch1-5
> 39.73% lzo1x_1_do_compress (real work)
> 14.96% page_vma_mapped_walk
> 6.97% _raw_spin_unlock_irq
> 3.07% do_raw_spin_lock
> 2.53% anon_vma_interval_tree_iter_first
> 2.04% ptep_clear_flush
> 1.82% __zram_bvec_write
> 1.76% __anon_vma_interval_tree_subtree_search
> 1.57% memmove
> 1.45% free_unref_page_list
>
> Configurations:
> CPU: single Snapdragon 7c
> Mem: total 4G
>
> Chrome OS MemoryPressure [1]
>
> [1] https://chromium.googlesource.com/chromiumos/platform/tast-tests/
>
In shrink_active_list we do preferential treatment of VM_EXEC pages.
Do we do similar thing with MGLRU? if not why is that not needed?
if (page_referenced(page, 0, sc->target_mem_cgroup,
&vm_flags)) {
/*
* Identify referenced, file-backed active pages and
* give them one more trip around the active list. So
* that executable code get better chances to stay in
* memory under moderate memory pressure. Anon pages
* are not likely to be evicted by use-once streaming
* IO, plus JVM can create lots of anon VM_EXEC pages,
* so we ignore them here.
*/
if ((vm_flags & VM_EXEC) && page_is_file_lru(page)) {
nr_rotated += thp_nr_pages(page);
list_add(&page->lru, &l_active);
continue;
}
}
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