On Mon, Mar 21, 2022 at 7:01 AM Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxx> wrote: > > Yu Zhao <yuzhao@xxxxxxxxxx> 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? No, because MGLRU has a different set of assumptions than the active/inactive LRU does [1]. It provides mmapped pages with equal opportunities, and the tradeoff was discussed here [2]. Note that even with this preferential treatment of executable pages, plus other heuristics added since then, executable pages are still underprotected for at least desktop workloads [3]. And I can confirm the problem reported is genuine -- we recently accidentally removed our private patch that works around the problem for the last 12 years, and observed immediate consequences on a small portion of devices not using MGLRU [4]. [1] https://lore.kernel.org/linux-mm/20220309021230.721028-15-yuzhao@xxxxxxxxxx/ [2] https://lore.kernel.org/linux-mm/20220208081902.3550911-5-yuzhao@xxxxxxxxxx/ [3] https://lore.kernel.org/linux-mm/2dc51fc8-f14e-17ed-a8c6-0ec70423bf54@xxxxxxxxxxxxxxx/ [4] https://chromium-review.googlesource.com/c/chromiumos/third_party/kernel/+/3429559
