This lock is only needed to synchronize updating pool->next_shrink, right? Can we just use atomic operations instead? (e.g. cmpxchg()).
I'm not entirely sure. I think in the pool destroy path, we have to also put the next_shrink memcg, so there's that.
We can use xchg() to replace it with NULL, then put the memcg ref, no?
We can also just hold zswap_pools_lock while shrinking the memcg perhaps? It's not a contended lock anyway. It just feels weird to add a spinlock to protect one pointer.
if (pool->next_shrink == memcg)pool->next_shrink =mem_cgroup_iter(NULL, pool->next_shrink, NULL, true);spin_unlock(&pool->next_shrink_lock);}spin_unlock(&zswap_pools_lock);+}
/*********************************
- zswap entry functions
**********************************/ static struct kmem_cache *zswap_entry_cache;
-static struct zswap_entry *zswap_entry_cache_alloc(gfp_t gfp) +static struct zswap_entry *zswap_entry_cache_alloc(gfp_t gfp, int nid) { struct zswap_entry *entry;
entry = kmem_cache_alloc(zswap_entry_cache, gfp);
entry = kmem_cache_alloc_node(zswap_entry_cache, gfp, nid); if (!entry) return NULL; entry->refcount = 1;[..]
@@ -1233,15 +1369,15 @@ bool zswap_store(struct folio *folio) zswap_invalidate_entry(tree, dupentry); } spin_unlock(&tree->lock);
/** XXX: zswap reclaim does not work with cgroups yet. Without a* cgroup-aware entry LRU, we will push out entries system-wide based on* local cgroup limits.*/ objcg = get_obj_cgroup_from_folio(folio);if (objcg && !obj_cgroup_may_zswap(objcg))goto reject;
if (objcg && !obj_cgroup_may_zswap(objcg)) {memcg = get_mem_cgroup_from_objcg(objcg);if (shrink_memcg(memcg)) {mem_cgroup_put(memcg);goto reject;}mem_cgroup_put(memcg);Can we just use RCU here as well? (same around memcg_list_lru_alloc() call below).
For memcg_list_lru_alloc(): there's potentially sleeping in that piece of code I believe? I believe at the very least we'll have to use this gfp_t flag for it to be rcu-safe:
GFP_KERNEL | __GFP_NORETRY | __GFP_NOMEMALLOC | __GFP_NOWARN not sure the
Same go for this particular place IIRC - there's some sleeping done in zswap_writeback_entry(), correct?
Ah right, I missed this. My bad.