Changes in v3: - Improve the commit messages and comments, per Yosry. - Use percpu_ref_is_zero() for debug purpose, per Yosry. - Collect tag. - Link to v2: https://lore.kernel.org/r/20240210-zswap-global-lru-v2-0-fbee3b11a62e@xxxxxxxxxxxxx Changes in v2: - fix build error when !CONFIG_MEMCG_KMEM. - make zswap struct static and fix some error paths, per Yosry. - add another shrink_lock to protect zswap.next_shrink, per Yosry. - keep "WARN_ON(percpu_ref_tryget(&pool->ref))" in pool release path for debug, per Nhat. - improve the commit messages. - Link to v1: https://lore.kernel.org/r/20240210-zswap-global-lru-v1-0-853473d7b0da@xxxxxxxxxxxxx Dynamic pool creation has been supported for a long time, which maybe not used so much in practice. But with the per-memcg lru merged, the current structure of zswap_pool's lru and shrinker become less optimal. In the current structure, each zswap_pool has its own lru, shrinker and shrink_work, but only the latest zswap_pool will be the current used. 1. When memory has pressure, all shrinkers of zswap_pools will try to shrink its lru list, there is no order between them. 2. When zswap limit hit, only the last zswap_pool's shrink_work will try to shrink its own lru, which is inefficient. A more natural way is to have a global zswap lru shared between all zswap_pools, and so is the shrinker. The code becomes much simpler too. Another optimization is changing zswap_pool kref to percpu_ref, which will be taken reference by every zswap entry. So the scalability is better. Testing kernel build (32 threads) in tmpfs with memory.max=2GB. (zswap shrinker and writeback enabled with one 50GB swapfile, on a 128 CPUs x86-64 machine, below is the average of 5 runs) mm-unstable zswap-global-lru real 63.20 63.12 user 1061.75 1062.95 sys 268.74 264.44 Signed-off-by: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx> --- Chengming Zhou (2): mm/zswap: global lru and shrinker shared by all zswap_pools mm/zswap: change zswap_pool kref to percpu_ref mm/zswap.c | 207 +++++++++++++++++++++++++++---------------------------------- 1 file changed, 93 insertions(+), 114 deletions(-) --- base-commit: 191d97734e41a5c9f90a2f6636fdd335ae1d435d change-id: 20240210-zswap-global-lru-94d49316178b Best regards, -- Chengming Zhou <zhouchengming@xxxxxxxxxxxxx>
