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Message-ID: <CAKEwX=NXzpDbonY2K7O-bWJm60OE_FUGvyArpqyK9dLxhyvWAQ@mail.gmail.com>
Date:   Tue, 5 Dec 2023 10:49:29 -0800
From:   Nhat Pham <nphamcs@...il.com>
To:     Yosry Ahmed <yosryahmed@...gle.com>
Cc:     akpm@...ux-foundation.org, hannes@...xchg.org,
        cerasuolodomenico@...il.com, sjenning@...hat.com,
        ddstreet@...e.org, vitaly.wool@...sulko.com, mhocko@...nel.org,
        roman.gushchin@...ux.dev, shakeelb@...gle.com,
        muchun.song@...ux.dev, chrisl@...nel.org, linux-mm@...ck.org,
        kernel-team@...a.com, linux-kernel@...r.kernel.org,
        cgroups@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-kselftest@...r.kernel.org, shuah@...nel.org
Subject: Re: [PATCH v8 3/6] zswap: make shrinking memcg-aware

On Tue, Dec 5, 2023 at 10:21 AM Yosry Ahmed <yosryahmed@...gle.com> wrote:
>
> On Thu, Nov 30, 2023 at 11:40 AM Nhat Pham <nphamcs@...il.com> wrote:
> >
> > From: Domenico Cerasuolo <cerasuolodomenico@...il.com>
> >
> > Currently, we only have a single global LRU for zswap. This makes it
> > impossible to perform worload-specific shrinking - an memcg cannot
> > determine which pages in the pool it owns, and often ends up writing
> > pages from other memcgs. This issue has been previously observed in
> > practice and mitigated by simply disabling memcg-initiated shrinking:
> >
> > https://lore.kernel.org/all/20230530232435.3097106-1-nphamcs@gmail.com/T/#u
> >
> > This patch fully resolves the issue by replacing the global zswap LRU
> > with memcg- and NUMA-specific LRUs, and modify the reclaim logic:
> >
> > a) When a store attempt hits an memcg limit, it now triggers a
> >    synchronous reclaim attempt that, if successful, allows the new
> >    hotter page to be accepted by zswap.
> > b) If the store attempt instead hits the global zswap limit, it will
> >    trigger an asynchronous reclaim attempt, in which an memcg is
> >    selected for reclaim in a round-robin-like fashion.
> >
> > Signed-off-by: Domenico Cerasuolo <cerasuolodomenico@...il.com>
> > Co-developed-by: Nhat Pham <nphamcs@...il.com>
> > Signed-off-by: Nhat Pham <nphamcs@...il.com>
> > ---
> >  include/linux/memcontrol.h |   5 +
> >  include/linux/zswap.h      |   2 +
> >  mm/memcontrol.c            |   2 +
> >  mm/swap.h                  |   3 +-
> >  mm/swap_state.c            |  24 +++-
> >  mm/zswap.c                 | 269 +++++++++++++++++++++++++++++--------
> >  6 files changed, 245 insertions(+), 60 deletions(-)
> >
> > diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> > index 2bd7d14ace78..a308c8eacf20 100644
> > --- a/include/linux/memcontrol.h
> > +++ b/include/linux/memcontrol.h
> > @@ -1192,6 +1192,11 @@ static inline struct mem_cgroup *page_memcg_check(struct page *page)
> >         return NULL;
> >  }
> >
> > +static inline struct mem_cgroup *get_mem_cgroup_from_objcg(struct obj_cgroup *objcg)
> > +{
> > +       return NULL;
> > +}
> > +
> >  static inline bool folio_memcg_kmem(struct folio *folio)
> >  {
> >         return false;
> > diff --git a/include/linux/zswap.h b/include/linux/zswap.h
> > index 2a60ce39cfde..e571e393669b 100644
> > --- a/include/linux/zswap.h
> > +++ b/include/linux/zswap.h
> > @@ -15,6 +15,7 @@ bool zswap_load(struct folio *folio);
> >  void zswap_invalidate(int type, pgoff_t offset);
> >  void zswap_swapon(int type);
> >  void zswap_swapoff(int type);
> > +void zswap_memcg_offline_cleanup(struct mem_cgroup *memcg);
> >
> >  #else
> >
> > @@ -31,6 +32,7 @@ static inline bool zswap_load(struct folio *folio)
> >  static inline void zswap_invalidate(int type, pgoff_t offset) {}
> >  static inline void zswap_swapon(int type) {}
> >  static inline void zswap_swapoff(int type) {}
> > +static inline void zswap_memcg_offline_cleanup(struct mem_cgroup *memcg) {}
> >
> >  #endif
> >
> > diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> > index 470821d1ba1a..792ca21c5815 100644
> > --- a/mm/memcontrol.c
> > +++ b/mm/memcontrol.c
> > @@ -5614,6 +5614,8 @@ static void mem_cgroup_css_offline(struct cgroup_subsys_state *css)
> >         page_counter_set_min(&memcg->memory, 0);
> >         page_counter_set_low(&memcg->memory, 0);
> >
> > +       zswap_memcg_offline_cleanup(memcg);
> > +
> >         memcg_offline_kmem(memcg);
> >         reparent_shrinker_deferred(memcg);
> >         wb_memcg_offline(memcg);
> > diff --git a/mm/swap.h b/mm/swap.h
> > index 73c332ee4d91..c0dc73e10e91 100644
> > --- a/mm/swap.h
> > +++ b/mm/swap.h
> > @@ -51,7 +51,8 @@ struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
> >                                    struct swap_iocb **plug);
> >  struct page *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
> >                                      struct mempolicy *mpol, pgoff_t ilx,
> > -                                    bool *new_page_allocated);
> > +                                    bool *new_page_allocated,
> > +                                    bool skip_if_exists);
> >  struct page *swap_cluster_readahead(swp_entry_t entry, gfp_t flag,
> >                                     struct mempolicy *mpol, pgoff_t ilx);
> >  struct page *swapin_readahead(swp_entry_t entry, gfp_t flag,
> > diff --git a/mm/swap_state.c b/mm/swap_state.c
> > index 85d9e5806a6a..6c84236382f3 100644
> > --- a/mm/swap_state.c
> > +++ b/mm/swap_state.c
> > @@ -412,7 +412,8 @@ struct folio *filemap_get_incore_folio(struct address_space *mapping,
> >
> >  struct page *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
> >                                      struct mempolicy *mpol, pgoff_t ilx,
> > -                                    bool *new_page_allocated)
> > +                                    bool *new_page_allocated,
> > +                                    bool skip_if_exists)
> >  {
> >         struct swap_info_struct *si;
> >         struct folio *folio;
> > @@ -470,6 +471,17 @@ struct page *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
> >                 if (err != -EEXIST)
> >                         goto fail_put_swap;
> >
> > +               /*
> > +                * Protect against a recursive call to __read_swap_cache_async()
> > +                * on the same entry waiting forever here because SWAP_HAS_CACHE
> > +                * is set but the folio is not the swap cache yet. This can
> > +                * happen today if mem_cgroup_swapin_charge_folio() below
> > +                * triggers reclaim through zswap, which may call
> > +                * __read_swap_cache_async() in the writeback path.
> > +                */
> > +               if (skip_if_exists)
> > +                       goto fail_put_swap;
> > +
> >                 /*
> >                  * We might race against __delete_from_swap_cache(), and
> >                  * stumble across a swap_map entry whose SWAP_HAS_CACHE
> > @@ -537,7 +549,7 @@ struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
> >
> >         mpol = get_vma_policy(vma, addr, 0, &ilx);
> >         page = __read_swap_cache_async(entry, gfp_mask, mpol, ilx,
> > -                                       &page_allocated);
> > +                                       &page_allocated, false);
> >         mpol_cond_put(mpol);
> >
> >         if (page_allocated)
> > @@ -654,7 +666,7 @@ struct page *swap_cluster_readahead(swp_entry_t entry, gfp_t gfp_mask,
> >                 /* Ok, do the async read-ahead now */
> >                 page = __read_swap_cache_async(
> >                                 swp_entry(swp_type(entry), offset),
> > -                               gfp_mask, mpol, ilx, &page_allocated);
> > +                               gfp_mask, mpol, ilx, &page_allocated, false);
> >                 if (!page)
> >                         continue;
> >                 if (page_allocated) {
> > @@ -672,7 +684,7 @@ struct page *swap_cluster_readahead(swp_entry_t entry, gfp_t gfp_mask,
> >  skip:
> >         /* The page was likely read above, so no need for plugging here */
> >         page = __read_swap_cache_async(entry, gfp_mask, mpol, ilx,
> > -                                       &page_allocated);
> > +                                       &page_allocated, false);
> >         if (unlikely(page_allocated))
> >                 swap_readpage(page, false, NULL);
> >         return page;
> > @@ -827,7 +839,7 @@ static struct page *swap_vma_readahead(swp_entry_t targ_entry, gfp_t gfp_mask,
> >                 pte_unmap(pte);
> >                 pte = NULL;
> >                 page = __read_swap_cache_async(entry, gfp_mask, mpol, ilx,
> > -                                               &page_allocated);
> > +                                               &page_allocated, false);
> >                 if (!page)
> >                         continue;
> >                 if (page_allocated) {
> > @@ -847,7 +859,7 @@ static struct page *swap_vma_readahead(swp_entry_t targ_entry, gfp_t gfp_mask,
> >  skip:
> >         /* The page was likely read above, so no need for plugging here */
> >         page = __read_swap_cache_async(targ_entry, gfp_mask, mpol, targ_ilx,
> > -                                       &page_allocated);
> > +                                       &page_allocated, false);
> >         if (unlikely(page_allocated))
> >                 swap_readpage(page, false, NULL);
> >         return page;
> > diff --git a/mm/zswap.c b/mm/zswap.c
> > index 4bdb2d83bb0d..f323e45cbdc7 100644
> > --- a/mm/zswap.c
> > +++ b/mm/zswap.c
> > @@ -35,6 +35,7 @@
> >  #include <linux/writeback.h>
> >  #include <linux/pagemap.h>
> >  #include <linux/workqueue.h>
> > +#include <linux/list_lru.h>
> >
> >  #include "swap.h"
> >  #include "internal.h"
> > @@ -174,8 +175,8 @@ struct zswap_pool {
> >         struct work_struct shrink_work;
> >         struct hlist_node node;
> >         char tfm_name[CRYPTO_MAX_ALG_NAME];
> > -       struct list_head lru;
> > -       spinlock_t lru_lock;
> > +       struct list_lru list_lru;
> > +       struct mem_cgroup *next_shrink;
> >  };
> >
> >  /*
> > @@ -291,15 +292,46 @@ static void zswap_update_total_size(void)
> >         zswap_pool_total_size = total;
> >  }
> >
> > +/* should be called under RCU */
>
> nit: probably WARN_ON_ONCE(!rcu_read_lock_held()) or
> RCU_LOCKDEP_WARN(!rcu_read_lock_held()) in the function body is
> better?
>
> > +#ifdef CONFIG_MEMCG
> > +static inline struct mem_cgroup *mem_cgroup_from_entry(struct zswap_entry *entry)
> > +{
> > +       return entry->objcg ? obj_cgroup_memcg(entry->objcg) : NULL;
> > +}
> > +#else
> > +static inline struct mem_cgroup *mem_cgroup_from_entry(struct zswap_entry *entry)
> > +{
> > +       return NULL;
> > +}
> > +#endif
> > +
> > +static inline int entry_to_nid(struct zswap_entry *entry)
> > +{
> > +       return page_to_nid(virt_to_page(entry));
> > +}
> > +
> > +void zswap_memcg_offline_cleanup(struct mem_cgroup *memcg)
> > +{
> > +       struct zswap_pool *pool;
> > +
> > +       /* lock out zswap pools list modification */
> > +       spin_lock(&zswap_pools_lock);
> > +       list_for_each_entry(pool, &zswap_pools, list) {
> > +               if (pool->next_shrink == memcg)
> > +                       pool->next_shrink = mem_cgroup_iter(NULL, pool->next_shrink, NULL);
> > +       }
> > +       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;
> > @@ -312,6 +344,61 @@ static void zswap_entry_cache_free(struct zswap_entry *entry)
> >         kmem_cache_free(zswap_entry_cache, entry);
> >  }
> >
> > +/*********************************
> > +* lru functions
> > +**********************************/
> > +static void zswap_lru_add(struct list_lru *list_lru, struct zswap_entry *entry)
> > +{
> > +       int nid = entry_to_nid(entry);
> > +       struct mem_cgroup *memcg;
> > +
> > +       /*
> > +        * Note that it is safe to use rcu_read_lock() here, even in the face of
> > +        * concurrent memcg offlining. Thanks to the memcg->kmemcg_id indirection
> > +        * used in list_lru lookup, only two scenarios are possible:
> > +        *
> > +        * 1. list_lru_add() is called before memcg->kmemcg_id is updated. The
> > +        *    new entry will be reparented to memcg's parent's list_lru.
> > +        * 2. list_lru_add() is called after memcg->kmemcg_id is updated. The
> > +        *    new entry will be added directly to memcg's parent's list_lru.
> > +        *
> > +        * Similar reasoning holds for list_lru_del() and list_lru_putback().
> > +        */
> > +       rcu_read_lock();
> > +       memcg = mem_cgroup_from_entry(entry);
> > +       /* will always succeed */
> > +       list_lru_add(list_lru, &entry->lru, nid, memcg);
> > +       rcu_read_unlock();
> > +}
> > +
> > +static void zswap_lru_del(struct list_lru *list_lru, struct zswap_entry *entry)
> > +{
> > +       int nid = entry_to_nid(entry);
> > +       struct mem_cgroup *memcg;
> > +
> > +       rcu_read_lock();
> > +       memcg = mem_cgroup_from_entry(entry);
> > +       /* will always succeed */
> > +       list_lru_del(list_lru, &entry->lru, nid, memcg);
> > +       rcu_read_unlock();
> > +}
> > +
> > +static void zswap_lru_putback(struct list_lru *list_lru,
> > +               struct zswap_entry *entry)
> > +{
> > +       int nid = entry_to_nid(entry);
> > +       spinlock_t *lock = &list_lru->node[nid].lock;
> > +       struct mem_cgroup *memcg;
> > +
> > +       rcu_read_lock();
> > +       memcg = mem_cgroup_from_entry(entry);
> > +       spin_lock(lock);
> > +       /* we cannot use list_lru_add here, because it increments node's lru count */
> > +       list_lru_putback(list_lru, &entry->lru, nid, memcg);
> > +       spin_unlock(lock);
> > +       rcu_read_unlock();
> > +}
> > +
> >  /*********************************
> >  * rbtree functions
> >  **********************************/
> > @@ -396,9 +483,7 @@ static void zswap_free_entry(struct zswap_entry *entry)
> >         if (!entry->length)
> >                 atomic_dec(&zswap_same_filled_pages);
> >         else {
> > -               spin_lock(&entry->pool->lru_lock);
> > -               list_del(&entry->lru);
> > -               spin_unlock(&entry->pool->lru_lock);
> > +               zswap_lru_del(&entry->pool->list_lru, entry);
> >                 zpool_free(zswap_find_zpool(entry), entry->handle);
> >                 zswap_pool_put(entry->pool);
> >         }
> > @@ -632,21 +717,15 @@ static void zswap_invalidate_entry(struct zswap_tree *tree,
> >                 zswap_entry_put(tree, entry);
> >  }
> >
> > -static int zswap_reclaim_entry(struct zswap_pool *pool)
> > +static enum lru_status shrink_memcg_cb(struct list_head *item, struct list_lru_one *l,
> > +                                      spinlock_t *lock, void *arg)
> >  {
> > -       struct zswap_entry *entry;
> > +       struct zswap_entry *entry = container_of(item, struct zswap_entry, lru);
> >         struct zswap_tree *tree;
> >         pgoff_t swpoffset;
> > -       int ret;
> > +       enum lru_status ret = LRU_REMOVED_RETRY;
> > +       int writeback_result;
> >
> > -       /* Get an entry off the LRU */
> > -       spin_lock(&pool->lru_lock);
> > -       if (list_empty(&pool->lru)) {
> > -               spin_unlock(&pool->lru_lock);
> > -               return -EINVAL;
> > -       }
> > -       entry = list_last_entry(&pool->lru, struct zswap_entry, lru);
> > -       list_del_init(&entry->lru);
> >         /*
> >          * Once the lru lock is dropped, the entry might get freed. The
> >          * swpoffset is copied to the stack, and entry isn't deref'd again
> > @@ -654,28 +733,32 @@ static int zswap_reclaim_entry(struct zswap_pool *pool)
> >          */
> >         swpoffset = swp_offset(entry->swpentry);
> >         tree = zswap_trees[swp_type(entry->swpentry)];
> > -       spin_unlock(&pool->lru_lock);
> > +       list_lru_isolate(l, item);
> > +       /*
> > +        * It's safe to drop the lock here because we return either
> > +        * LRU_REMOVED_RETRY or LRU_RETRY.
> > +        */
> > +       spin_unlock(lock);
> >
> >         /* Check for invalidate() race */
> >         spin_lock(&tree->lock);
> > -       if (entry != zswap_rb_search(&tree->rbroot, swpoffset)) {
> > -               ret = -EAGAIN;
> > +       if (entry != zswap_rb_search(&tree->rbroot, swpoffset))
> >                 goto unlock;
> > -       }
> > +
> >         /* Hold a reference to prevent a free during writeback */
> >         zswap_entry_get(entry);
> >         spin_unlock(&tree->lock);
> >
> > -       ret = zswap_writeback_entry(entry, tree);
> > +       writeback_result = zswap_writeback_entry(entry, tree);
> >
> >         spin_lock(&tree->lock);
> > -       if (ret) {
> > -               /* Writeback failed, put entry back on LRU */
> > -               spin_lock(&pool->lru_lock);
> > -               list_move(&entry->lru, &pool->lru);
> > -               spin_unlock(&pool->lru_lock);
> > +       if (writeback_result) {
> > +               zswap_reject_reclaim_fail++;
> > +               zswap_lru_putback(&entry->pool->list_lru, entry);
> > +               ret = LRU_RETRY;
> >                 goto put_unlock;
> >         }
> > +       zswap_written_back_pages++;
> >
> >         /*
> >          * Writeback started successfully, the page now belongs to the
> > @@ -689,27 +772,93 @@ static int zswap_reclaim_entry(struct zswap_pool *pool)
> >         zswap_entry_put(tree, entry);
> >  unlock:
> >         spin_unlock(&tree->lock);
> > -       return ret ? -EAGAIN : 0;
> > +       spin_lock(lock);
> > +       return ret;
> > +}
> > +
> > +static int shrink_memcg(struct mem_cgroup *memcg)
> > +{
> > +       struct zswap_pool *pool;
> > +       int nid, shrunk = 0;
> > +
> > +       /*
> > +        * Skip zombies because their LRUs are reparented and we would be
> > +        * reclaiming from the parent instead of the dead memcg.
> > +        */
> > +       if (memcg && !mem_cgroup_online(memcg))
> > +               return -ENOENT;
> > +
> > +       pool = zswap_pool_current_get();
> > +       if (!pool)
> > +               return -EINVAL;
> > +
> > +       for_each_node_state(nid, N_NORMAL_MEMORY) {
> > +               unsigned long nr_to_walk = 1;
> > +
> > +               shrunk += list_lru_walk_one(&pool->list_lru, nid, memcg,
> > +                                           &shrink_memcg_cb, NULL, &nr_to_walk);
> > +       }
> > +       zswap_pool_put(pool);
> > +       return shrunk ? 0 : -EAGAIN;
> >  }
> >
> >  static void shrink_worker(struct work_struct *w)
> >  {
> >         struct zswap_pool *pool = container_of(w, typeof(*pool),
> >                                                 shrink_work);
> > +       struct mem_cgroup *memcg;
> >         int ret, failures = 0;
> >
> > +       /* global reclaim will select cgroup in a round-robin fashion. */
> >         do {
> > -               ret = zswap_reclaim_entry(pool);
> > -               if (ret) {
> > -                       zswap_reject_reclaim_fail++;
> > -                       if (ret != -EAGAIN)
> > +               spin_lock(&zswap_pools_lock);
> > +               pool->next_shrink = mem_cgroup_iter(NULL, pool->next_shrink, NULL);
> > +               memcg = pool->next_shrink;
> > +
> > +               /*
> > +                * We need to retry if we have gone through a full round trip, or if we
> > +                * got an offline memcg (or else we risk undoing the effect of the
> > +                * zswap memcg offlining cleanup callback). This is not catastrophic
> > +                * per se, but it will keep the now offlined memcg hostage for a while.
> > +                *
> > +                * Note that if we got an online memcg, we will keep the extra
> > +                * reference in case the original reference obtained by mem_cgroup_iter
> > +                * is dropped by the zswap memcg offlining callback, ensuring that the
> > +                * memcg is not killed when we are reclaiming.
> > +                */
> > +               if (!memcg) {
> > +                       spin_unlock(&zswap_pools_lock);
> > +                       if (++failures == MAX_RECLAIM_RETRIES)
> >                                 break;
> > +
> > +                       goto resched;
> > +               }
> > +
> > +               if (!mem_cgroup_online(memcg)) {
> > +                       /* drop the reference from mem_cgroup_iter() */
> > +                       mem_cgroup_put(memcg);
>
> Probably better to use mem_cgroup_iter_break() here?

mem_cgroup_iter_break(NULL, memcg) seems to perform the same thing, right?

>
> Also, I don't see mem_cgroup_tryget_online() being used here (where I
> expected it to be used), did I miss it?

Oh shoot yeah that was a typo - it should be
mem_cgroup_tryget_online(). Let me send a fix to that.

>
> > +                       pool->next_shrink = NULL;
> > +                       spin_unlock(&zswap_pools_lock);
> > +
> >                         if (++failures == MAX_RECLAIM_RETRIES)
> >                                 break;
> > +
> > +                       goto resched;
> >                 }
> > +               spin_unlock(&zswap_pools_lock);
> > +
> > +               ret = shrink_memcg(memcg);
>
> We just checked for online-ness above, and then shrink_memcg() checks
> it again. Is this intentional?

Hmm these two checks are for two different purposes. The check above
is mainly to prevent accidentally undoing the offline cleanup callback
during memcg selection step. Inside shrink_memcg(), we check
onlineness again to prevent reclaiming from offlined memcgs - which in
effect will trigger the reclaim of the parent's memcg.

>
> > +               /* drop the extra reference */
>
> Where does the extra reference come from?

The extra reference is from mem_cgroup_tryget_online(). We get two
references in the dance above - one from mem_cgroup_iter() (which can
be dropped) and one extra from mem_cgroup_tryget_online(). I kept the
second one in case the first one was dropped by the zswap memcg
offlining callback, but after reclaiming it is safe to just drop it.

>
> > +               mem_cgroup_put(memcg);
> > +
> > +               if (ret == -EINVAL)
> > +                       break;
> > +               if (ret && ++failures == MAX_RECLAIM_RETRIES)
> > +                       break;
> > +
> > +resched:
> >                 cond_resched();
> >         } while (!zswap_can_accept());
> > -       zswap_pool_put(pool);
> >  }
> >
> >  static struct zswap_pool *zswap_pool_create(char *type, char *compressor)
> > @@ -767,8 +916,7 @@ static struct zswap_pool *zswap_pool_create(char *type, char *compressor)
> >          */
> >         kref_init(&pool->kref);
> >         INIT_LIST_HEAD(&pool->list);
> > -       INIT_LIST_HEAD(&pool->lru);
> > -       spin_lock_init(&pool->lru_lock);
> > +       list_lru_init_memcg(&pool->list_lru, NULL);
> >         INIT_WORK(&pool->shrink_work, shrink_worker);
> >
> >         zswap_pool_debug("created", pool);
> > @@ -834,6 +982,13 @@ static void zswap_pool_destroy(struct zswap_pool *pool)
> >
> >         cpuhp_state_remove_instance(CPUHP_MM_ZSWP_POOL_PREPARE, &pool->node);
> >         free_percpu(pool->acomp_ctx);
> > +       list_lru_destroy(&pool->list_lru);
> > +
> > +       spin_lock(&zswap_pools_lock);
> > +       mem_cgroup_put(pool->next_shrink);
> > +       pool->next_shrink = NULL;
> > +       spin_unlock(&zswap_pools_lock);
> > +
> >         for (i = 0; i < ZSWAP_NR_ZPOOLS; i++)
> >                 zpool_destroy_pool(pool->zpools[i]);
> >         kfree(pool);
> > @@ -1081,7 +1236,7 @@ static int zswap_writeback_entry(struct zswap_entry *entry,
> >         /* try to allocate swap cache page */
> >         mpol = get_task_policy(current);
> >         page = __read_swap_cache_async(swpentry, GFP_KERNEL, mpol,
> > -                               NO_INTERLEAVE_INDEX, &page_was_allocated);
> > +                               NO_INTERLEAVE_INDEX, &page_was_allocated, true);
> >         if (!page) {
> >                 ret = -ENOMEM;
> >                 goto fail;
> > @@ -1152,7 +1307,6 @@ static int zswap_writeback_entry(struct zswap_entry *entry,
> >         /* start writeback */
> >         __swap_writepage(page, &wbc);
> >         put_page(page);
> > -       zswap_written_back_pages++;
> >
> >         return ret;
> >
> > @@ -1209,6 +1363,7 @@ bool zswap_store(struct folio *folio)
> >         struct scatterlist input, output;
> >         struct crypto_acomp_ctx *acomp_ctx;
> >         struct obj_cgroup *objcg = NULL;
> > +       struct mem_cgroup *memcg = NULL;
> >         struct zswap_pool *pool;
> >         struct zpool *zpool;
> >         unsigned int dlen = PAGE_SIZE;
> > @@ -1240,15 +1395,15 @@ 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);
>
> Do we need a reference here? IIUC, this is folio_memcg() and the folio
> is locked, so folio_memcg() should remain stable, no?

Hmmm obj_cgroup_may_zswap() also holds a reference to the objcg's
memcg, so I just followed the patterns to be safe.


>
> Same for the call below.
>
> > +               if (shrink_memcg(memcg)) {
> > +                       mem_cgroup_put(memcg);
> > +                       goto reject;
> > +               }
> > +               mem_cgroup_put(memcg);
> > +       }
> >
> >         /* reclaim space if needed */
> >         if (zswap_is_full()) {
> > @@ -1265,7 +1420,7 @@ bool zswap_store(struct folio *folio)
> >         }
> >
> >         /* allocate entry */
> > -       entry = zswap_entry_cache_alloc(GFP_KERNEL);
> > +       entry = zswap_entry_cache_alloc(GFP_KERNEL, page_to_nid(page));
> >         if (!entry) {
> >                 zswap_reject_kmemcache_fail++;
> >                 goto reject;
> > @@ -1292,6 +1447,15 @@ bool zswap_store(struct folio *folio)
> >         if (!entry->pool)
> >                 goto freepage;
> >
> > +       if (objcg) {
> > +               memcg = get_mem_cgroup_from_objcg(objcg);
> > +               if (memcg_list_lru_alloc(memcg, &entry->pool->list_lru, GFP_KERNEL)) {
> > +                       mem_cgroup_put(memcg);
> > +                       goto put_pool;
> > +               }
> > +               mem_cgroup_put(memcg);
> > +       }
> > +
> >         /* compress */
> >         acomp_ctx = raw_cpu_ptr(entry->pool->acomp_ctx);
> >
> > @@ -1370,9 +1534,8 @@ bool zswap_store(struct folio *folio)
> >                 zswap_invalidate_entry(tree, dupentry);
> >         }
> >         if (entry->length) {
> > -               spin_lock(&entry->pool->lru_lock);
> > -               list_add(&entry->lru, &entry->pool->lru);
> > -               spin_unlock(&entry->pool->lru_lock);
> > +               INIT_LIST_HEAD(&entry->lru);
> > +               zswap_lru_add(&entry->pool->list_lru, entry);
> >         }
> >         spin_unlock(&tree->lock);
> >
> > @@ -1385,6 +1548,7 @@ bool zswap_store(struct folio *folio)
> >
> >  put_dstmem:
> >         mutex_unlock(acomp_ctx->mutex);
> > +put_pool:
> >         zswap_pool_put(entry->pool);
> >  freepage:
> >         zswap_entry_cache_free(entry);
> > @@ -1479,9 +1643,8 @@ bool zswap_load(struct folio *folio)
> >                 zswap_invalidate_entry(tree, entry);
> >                 folio_mark_dirty(folio);
> >         } else if (entry->length) {
> > -               spin_lock(&entry->pool->lru_lock);
> > -               list_move(&entry->lru, &entry->pool->lru);
> > -               spin_unlock(&entry->pool->lru_lock);
> > +               zswap_lru_del(&entry->pool->list_lru, entry);
> > +               zswap_lru_add(&entry->pool->list_lru, entry);
> >         }
> >         zswap_entry_put(tree, entry);
> >         spin_unlock(&tree->lock);
> > --
> > 2.34.1

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