Currently, every list_lru has a per-node lock that protects adding,
deletion, isolation, and reparenting of all list_lru_one instances
belonging to this list_lru on this node. This lock contention is heavy
when multiple cgroups modify the same list_lru.
This lock can be split into per-cgroup scope to reduce contention.
To achieve this, we need a stable list_lru_one for every cgroup. This
commit adds a lock to each list_lru_one and introduced a helper function
lock_list_lru_of_memcg, making it possible to pin the list_lru of a memcg.
Then reworked the reparenting process.
Reparenting will switch the list_lru_one instances one by one. By locking
each instance and marking it dead using the nr_items counter, reparenting
ensures that all items in the corresponding cgroup (on-list or not,
because items have a stable cgroup, see below) will see the list_lru_one
switch synchronously.
Objcg reparent is also moved after list_lru reparent so items will have a
stable mem cgroup until all list_lru_one instances are drained.
The only caller that doesn't work the *_obj interfaces are direct calls to
list_lru_{add,del}. But it's only used by zswap and that's also based on
objcg, so it's fine.
This also changes the bahaviour of the isolation function when LRU_RETRY
or LRU_REMOVED_RETRY is returned, because now releasing the lock could
unblock reparenting and free the list_lru_one, isolation function will
have to return withoug re-lock the lru.
prepare() {
mkdir /tmp/test-fs
modprobe brd rd_nr=1 rd_size=33554432
mkfs.xfs -f /dev/ram0
mount -t xfs /dev/ram0 /tmp/test-fs
for i in $(seq 1 512); do
mkdir "/tmp/test-fs/$i"
for j in $(seq 1 10240); do
echo TEST-CONTENT > "/tmp/test-fs/$i/$j"
done &
done; wait
}
do_test() {
read_worker() {
sleep 1
tar -cv "$1" &>/dev/null
}
read_in_all() {
cd "/tmp/test-fs" && ls
for i in $(seq 1 512); do
(exec sh -c 'echo "$PPID"') > "/sys/fs/cgroup/benchmark/$i/cgroup.procs"
read_worker "$i" &
done; wait
}
for i in $(seq 1 512); do
mkdir -p "/sys/fs/cgroup/benchmark/$i"
done
echo +memory > /sys/fs/cgroup/benchmark/cgroup.subtree_control
echo 512M > /sys/fs/cgroup/benchmark/memory.max
echo 3 > /proc/sys/vm/drop_caches
time read_in_all
}
Above script simulates compression of small files in multiple cgroups
with memory pressure. Run prepare() then do_test for 6 times:
Before:
real 0m7.762s user 0m11.340s sys 3m11.224s
real 0m8.123s user 0m11.548s sys 3m2.549s
real 0m7.736s user 0m11.515s sys 3m11.171s
real 0m8.539s user 0m11.508s sys 3m7.618s
real 0m7.928s user 0m11.349s sys 3m13.063s
real 0m8.105s user 0m11.128s sys 3m14.313s
After this commit (about ~15% faster):
real 0m6.953s user 0m11.327s sys 2m42.912s
real 0m7.453s user 0m11.343s sys 2m51.942s
real 0m6.916s user 0m11.269s sys 2m43.957s
real 0m6.894s user 0m11.528s sys 2m45.346s
real 0m6.911s user 0m11.095s sys 2m43.168s
real 0m6.773s user 0m11.518s sys 2m40.774s
Link: https://lkml.kernel.org/r/20241104175257.60853-6-ryncsn@gmail.com
Signed-off-by: Kairui Song <kasong@tencent.com>
Cc: Chengming Zhou <zhouchengming@bytedance.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Qi Zheng <zhengqi.arch@bytedance.com>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Waiman Long <longman@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
fb56fdf8b9