From: Sergey Senozhatsky senozhatsky@chromium.org
commit d2658f2052c7db6ec0a79977205f8cf1cb9effc2 upstream.
zsmalloc pool can be compacted concurrently by many contexts, e.g.
cc1 handle_mm_fault() do_anonymous_page() __alloc_pages_slowpath() try_to_free_pages() do_try_to_free_pages( lru_gen_shrink_node() shrink_slab() do_shrink_slab() zs_shrinker_scan() zs_compact()
Pool compaction is currently (basically) single-threaded as it is performed under pool->lock. Having multiple compaction threads results in unnecessary contention, as each thread competes for pool->lock. This, in turn, affects all zsmalloc operations such as zs_malloc(), zs_map_object(), zs_free(), etc.
Introduce the pool->compaction_in_progress atomic variable, which ensures that only one compaction context can run at a time. This reduces overall pool->lock contention in (corner) cases when many contexts attempt to shrink zspool simultaneously.
Link: https://lkml.kernel.org/r/20230418074639.1903197-1-senozhatsky@chromium.org Fixes: c0547d0b6a4b ("zsmalloc: consolidate zs_pool's migrate_lock and size_class's locks") Signed-off-by: Sergey Senozhatsky senozhatsky@chromium.org Reviewed-by: Yosry Ahmed yosryahmed@google.com Cc: Minchan Kim minchan@kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- mm/zsmalloc.c | 12 ++++++++++++ 1 file changed, 12 insertions(+)
--- a/mm/zsmalloc.c +++ b/mm/zsmalloc.c @@ -246,6 +246,7 @@ struct zs_pool { struct work_struct free_work; #endif spinlock_t lock; + atomic_t compaction_in_progress; };
struct zspage { @@ -2100,6 +2101,15 @@ unsigned long zs_compact(struct zs_pool struct size_class *class; unsigned long pages_freed = 0;
+ /* + * Pool compaction is performed under pool->lock so it is basically + * single-threaded. Having more than one thread in __zs_compact() + * will increase pool->lock contention, which will impact other + * zsmalloc operations that need pool->lock. + */ + if (atomic_xchg(&pool->compaction_in_progress, 1)) + return 0; + for (i = ZS_SIZE_CLASSES - 1; i >= 0; i--) { class = pool->size_class[i]; if (class->index != i) @@ -2107,6 +2117,7 @@ unsigned long zs_compact(struct zs_pool pages_freed += __zs_compact(pool, class); } atomic_long_add(pages_freed, &pool->stats.pages_compacted); + atomic_set(&pool->compaction_in_progress, 0);
return pages_freed; } @@ -2193,6 +2204,7 @@ struct zs_pool *zs_create_pool(const cha
init_deferred_free(pool); spin_lock_init(&pool->lock); + atomic_set(&pool->compaction_in_progress, 0);
pool->name = kstrdup(name, GFP_KERNEL); if (!pool->name)