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? 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; } }
