diff mbox series

[RFC,1/7] mm: zswap: add pool shrinking mechanism

Message ID 20230605085419.44383-2-cerasuolodomenico@gmail.com
State New
Headers
Series mm: zswap: move writeback LRU from zpool to zswap |

Commit Message

Domenico Cerasuolo June 5, 2023, 8:54 a.m. UTC 
  Each zpool driver (zbud, z3fold and zsmalloc) implements its own shrink
function, which is called from zpool_shrink. However, with this commit,
a unified shrink function is added to zswap. The ultimate goal is to
eliminate the need for zpool_shrink once all zpool implementations have
dropped their shrink code.

To ensure the functionality of each commit, this change focuses solely
on adding the mechanism itself. No modifications are made to
the backends, meaning that functionally, there are no immediate changes.
The zswap mechanism will only come into effect once the backends have
removed their shrink code. The subsequent commits will address the
modifications needed in the backends.

Signed-off-by: Domenico Cerasuolo <cerasuolodomenico@gmail.com>
---
 mm/zswap.c | 83 ++++++++++++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 78 insertions(+), 5 deletions(-)

Comments

Johannes Weiner June 5, 2023, 3:29 p.m. UTC | #1 
Hi Domenico,

On Mon, Jun 05, 2023 at 10:54:13AM +0200, Domenico Cerasuolo wrote:
> @@ -364,6 +369,9 @@ static void zswap_free_entry(struct zswap_entry *entry)
>  	if (!entry->length)
>  		atomic_dec(&zswap_same_filled_pages);
>  	else {
> +		spin_lock(&entry->pool->lock);
> +		list_del_init(&entry->lru);
> +		spin_unlock(&entry->pool->lock);

This should be list_del(), as the entry is freed right after this and
the list isn't reused anymore.

The slab memory is recycled, but the allocation site (commented on
below) doesn't need the list initialized.

However, I think it also needs to check !zpool_evictable(). If
alloc/store doesn't do the list_add(), this would be a double delete.

> @@ -584,14 +592,65 @@ static struct zswap_pool *zswap_pool_find_get(char *type, char *compressor)
>  	return NULL;
>  }
>  
> +static int zswap_shrink(struct zswap_pool *pool)
> +{
> +	struct zswap_entry *lru_entry, *tree_entry = NULL;
> +	struct zswap_header *zhdr;
> +	struct zswap_tree *tree;
> +	swp_entry_t swpentry;
> +	int ret;
> +
> +	/* get a reclaimable entry from LRU */
> +	spin_lock(&pool->lock);
> +	if (list_empty(&pool->lru)) {
> +		spin_unlock(&pool->lock);
> +		return -EINVAL;
> +	}
> +	lru_entry = list_last_entry(&pool->lru, struct zswap_entry, lru);
> +	list_del_init(&lru_entry->lru);
> +	zhdr = zpool_map_handle(pool->zpool, lru_entry->handle, ZPOOL_MM_RO);
> +	tree = zswap_trees[swp_type(zhdr->swpentry)];
> +	zpool_unmap_handle(pool->zpool, lru_entry->handle);
> +	swpentry = zhdr->swpentry;
> +	spin_unlock(&pool->lock);

Once the pool lock is dropped, the lru_entry might get freed. But the
swpentry is copied to the stack, and lru_entry isn't deref'd again
until the entry is verified to still be alive in the tree.

This could use a comment.

> +	/* hold a reference from tree so it won't be freed during writeback */
> +	spin_lock(&tree->lock);
> +	tree_entry = zswap_entry_find_get(&tree->rbroot, swp_offset(swpentry));
> +	if (tree_entry != lru_entry) {
> +		if (tree_entry)
> +			zswap_entry_put(tree, tree_entry);
> +		spin_unlock(&tree->lock);
> +		return -EAGAIN;
> +	}
> +	spin_unlock(&tree->lock);

It's pretty outrageous how much simpler this is compared to the
<backend>_reclaim_page() functions! The backends have to jump through
a lot of hoops to serialize against freeing, whereas zswap can simply
hold a reference. This is clearly a much better design.

> +	ret = zswap_writeback_entry(pool->zpool, lru_entry->handle);
> +
> +	spin_lock(&tree->lock);
> +	if (ret) {
> +		spin_lock(&pool->lock);
> +		list_move(&lru_entry->lru, &pool->lru);
> +		spin_unlock(&pool->lock);
> +	}
> +	zswap_entry_put(tree, tree_entry);
> +	spin_unlock(&tree->lock);
> +
> +	return ret ? -EAGAIN : 0;
> +}
> +
>  static void shrink_worker(struct work_struct *w)
>  {
>  	struct zswap_pool *pool = container_of(w, typeof(*pool),
>  						shrink_work);
>  	int ret, failures = 0;
>  
> +	/* zpool_evictable will be removed once all 3 backends have migrated*/

Missing space between text and */

>  	do {
> -		ret = zpool_shrink(pool->zpool, 1, NULL);
> +		if (zpool_evictable(pool->zpool))
> +			ret = zpool_shrink(pool->zpool, 1, NULL);
> +		else
> +			ret = zswap_shrink(pool);
>  		if (ret) {
>  			zswap_reject_reclaim_fail++;
>  			if (ret != -EAGAIN)
> @@ -655,6 +714,8 @@ 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->lock);
>  	INIT_WORK(&pool->shrink_work, shrink_worker);
>  
>  	zswap_pool_debug("created", pool);
> @@ -1270,7 +1331,7 @@ static int zswap_frontswap_store(unsigned type, pgoff_t offset,
>  	}
>  
>  	/* store */
> -	hlen = zpool_evictable(entry->pool->zpool) ? sizeof(zhdr) : 0;
> +	hlen = sizeof(zhdr);
>  	gfp = __GFP_NORETRY | __GFP_NOWARN | __GFP_KSWAPD_RECLAIM;
>  	if (zpool_malloc_support_movable(entry->pool->zpool))
>  		gfp |= __GFP_HIGHMEM | __GFP_MOVABLE;
> @@ -1313,6 +1374,13 @@ static int zswap_frontswap_store(unsigned type, pgoff_t offset,
>  			zswap_entry_put(tree, dupentry);
>  		}
>  	} while (ret == -EEXIST);
> +	INIT_LIST_HEAD(&entry->lru);

The list_add() below initializes the entry, so this shouldn't be
needed.

> +	/* zpool_evictable will be removed once all 3 backends have migrated*/
> +	if (entry->length && !zpool_evictable(entry->pool->zpool)) {
> +		spin_lock(&entry->pool->lock);
> +		list_add(&entry->lru, &entry->pool->lru);
> +		spin_unlock(&entry->pool->lock);
> +	}
>  	spin_unlock(&tree->lock);
>  
>  	/* update stats */
Yosry Ahmed June 6, 2023, 2:18 a.m. UTC | #2 
Hi Domenico,

On Mon, Jun 5, 2023 at 1:54 AM Domenico Cerasuolo
<cerasuolodomenico@gmail.com> wrote:
>
> Each zpool driver (zbud, z3fold and zsmalloc) implements its own shrink
> function, which is called from zpool_shrink. However, with this commit,
> a unified shrink function is added to zswap. The ultimate goal is to
> eliminate the need for zpool_shrink once all zpool implementations have
> dropped their shrink code.
>
> To ensure the functionality of each commit, this change focuses solely
> on adding the mechanism itself. No modifications are made to
> the backends, meaning that functionally, there are no immediate changes.
> The zswap mechanism will only come into effect once the backends have
> removed their shrink code. The subsequent commits will address the
> modifications needed in the backends.
>
> Signed-off-by: Domenico Cerasuolo <cerasuolodomenico@gmail.com>
> ---
>  mm/zswap.c | 83 ++++++++++++++++++++++++++++++++++++++++++++++++++----
>  1 file changed, 78 insertions(+), 5 deletions(-)
>
> diff --git a/mm/zswap.c b/mm/zswap.c
> index bcb82e09eb64..80d7780bf066 100644
> --- a/mm/zswap.c
> +++ b/mm/zswap.c
> @@ -159,6 +159,8 @@ 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 lock;

If this lock is only protecting the lru then I believe it's better to
call in lru_lock to make it explicit.

>  };
>
>  /*
> @@ -176,10 +178,12 @@ struct zswap_pool {
>   *            be held while changing the refcount.  Since the lock must
>   *            be held, there is no reason to also make refcount atomic.
>   * length - the length in bytes of the compressed page data.  Needed during
> - *          decompression. For a same value filled page length is 0.
> + *          decompression. For a same value filled page length is 0, and both
> + *          pool and lru are invalid and must be ignored.
>   * pool - the zswap_pool the entry's data is in
>   * handle - zpool allocation handle that stores the compressed page data
>   * value - value of the same-value filled pages which have same content
> + * lru - handle to the pool's lru used to evict pages.
>   */
>  struct zswap_entry {
>         struct rb_node rbnode;
> @@ -192,6 +196,7 @@ struct zswap_entry {
>                 unsigned long value;
>         };
>         struct obj_cgroup *objcg;
> +       struct list_head lru;
>  };
>
>  struct zswap_header {
> @@ -364,6 +369,9 @@ static void zswap_free_entry(struct zswap_entry *entry)
>         if (!entry->length)
>                 atomic_dec(&zswap_same_filled_pages);
>         else {
> +               spin_lock(&entry->pool->lock);
> +               list_del_init(&entry->lru);
> +               spin_unlock(&entry->pool->lock);

I think we should document the lock ordering somewhere (tree lock ->
lru lock), otherwise we may run into an ABBA deadlock down the road.

>                 zpool_free(entry->pool->zpool, entry->handle);
>                 zswap_pool_put(entry->pool);
>         }
> @@ -584,14 +592,65 @@ static struct zswap_pool *zswap_pool_find_get(char *type, char *compressor)
>         return NULL;
>  }
>
> +static int zswap_shrink(struct zswap_pool *pool)
> +{
> +       struct zswap_entry *lru_entry, *tree_entry = NULL;
> +       struct zswap_header *zhdr;
> +       struct zswap_tree *tree;
> +       swp_entry_t swpentry;
> +       int ret;
> +
> +       /* get a reclaimable entry from LRU */
> +       spin_lock(&pool->lock);
> +       if (list_empty(&pool->lru)) {
> +               spin_unlock(&pool->lock);
> +               return -EINVAL;
> +       }
> +       lru_entry = list_last_entry(&pool->lru, struct zswap_entry, lru);
> +       list_del_init(&lru_entry->lru);
> +       zhdr = zpool_map_handle(pool->zpool, lru_entry->handle, ZPOOL_MM_RO);
> +       tree = zswap_trees[swp_type(zhdr->swpentry)];
> +       zpool_unmap_handle(pool->zpool, lru_entry->handle);
> +       swpentry = zhdr->swpentry;
> +       spin_unlock(&pool->lock);
> +
> +       /* hold a reference from tree so it won't be freed during writeback */
> +       spin_lock(&tree->lock);
> +       tree_entry = zswap_entry_find_get(&tree->rbroot, swp_offset(swpentry));
> +       if (tree_entry != lru_entry) {
> +               if (tree_entry)
> +                       zswap_entry_put(tree, tree_entry);
> +               spin_unlock(&tree->lock);
> +               return -EAGAIN;
> +       }
> +       spin_unlock(&tree->lock);
> +
> +       ret = zswap_writeback_entry(pool->zpool, lru_entry->handle);
> +
> +       spin_lock(&tree->lock);
> +       if (ret) {
> +               spin_lock(&pool->lock);
> +               list_move(&lru_entry->lru, &pool->lru);
> +               spin_unlock(&pool->lock);
> +       }
> +       zswap_entry_put(tree, tree_entry);
> +       spin_unlock(&tree->lock);
> +
> +       return ret ? -EAGAIN : 0;
> +}
> +
>  static void shrink_worker(struct work_struct *w)
>  {
>         struct zswap_pool *pool = container_of(w, typeof(*pool),
>                                                 shrink_work);
>         int ret, failures = 0;
>
> +       /* zpool_evictable will be removed once all 3 backends have migrated*/
>         do {
> -               ret = zpool_shrink(pool->zpool, 1, NULL);
> +               if (zpool_evictable(pool->zpool))
> +                       ret = zpool_shrink(pool->zpool, 1, NULL);
> +               else
> +                       ret = zswap_shrink(pool);
>                 if (ret) {
>                         zswap_reject_reclaim_fail++;
>                         if (ret != -EAGAIN)
> @@ -655,6 +714,8 @@ 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->lock);
>         INIT_WORK(&pool->shrink_work, shrink_worker);
>
>         zswap_pool_debug("created", pool);
> @@ -1270,7 +1331,7 @@ static int zswap_frontswap_store(unsigned type, pgoff_t offset,
>         }
>
>         /* store */
> -       hlen = zpool_evictable(entry->pool->zpool) ? sizeof(zhdr) : 0;
> +       hlen = sizeof(zhdr);
>         gfp = __GFP_NORETRY | __GFP_NOWARN | __GFP_KSWAPD_RECLAIM;
>         if (zpool_malloc_support_movable(entry->pool->zpool))
>                 gfp |= __GFP_HIGHMEM | __GFP_MOVABLE;
> @@ -1313,6 +1374,13 @@ static int zswap_frontswap_store(unsigned type, pgoff_t offset,
>                         zswap_entry_put(tree, dupentry);
>                 }
>         } while (ret == -EEXIST);
> +       INIT_LIST_HEAD(&entry->lru);
> +       /* zpool_evictable will be removed once all 3 backends have migrated*/
> +       if (entry->length && !zpool_evictable(entry->pool->zpool)) {
> +               spin_lock(&entry->pool->lock);
> +               list_add(&entry->lru, &entry->pool->lru);
> +               spin_unlock(&entry->pool->lock);
> +       }
>         spin_unlock(&tree->lock);
>
>         /* update stats */
> @@ -1384,8 +1452,7 @@ static int zswap_frontswap_load(unsigned type, pgoff_t offset,
>         /* decompress */
>         dlen = PAGE_SIZE;
>         src = zpool_map_handle(entry->pool->zpool, entry->handle, ZPOOL_MM_RO);
> -       if (zpool_evictable(entry->pool->zpool))
> -               src += sizeof(struct zswap_header);
> +       src += sizeof(struct zswap_header);
>
>         if (!zpool_can_sleep_mapped(entry->pool->zpool)) {
>                 memcpy(tmp, src, entry->length);
> @@ -1415,6 +1482,12 @@ static int zswap_frontswap_load(unsigned type, pgoff_t offset,
>  freeentry:
>         spin_lock(&tree->lock);
>         zswap_entry_put(tree, entry);
> +       /* zpool_evictable will be removed once all 3 backends have migrated*/
> +       if (entry->length && !zpool_evictable(entry->pool->zpool)) {
> +               spin_lock(&entry->pool->lock);
> +               list_move(&entry->lru, &entry->pool->lru);
> +               spin_unlock(&entry->pool->lock);
> +       }
>         spin_unlock(&tree->lock);
>
>         return ret;
> --
> 2.34.1
>
Domenico Cerasuolo June 6, 2023, 9:31 a.m. UTC | #3 
On Mon, Jun 5, 2023 at 5:29 PM Johannes Weiner <hannes@cmpxchg.org> wrote:
>
> Hi Domenico,
>
> On Mon, Jun 05, 2023 at 10:54:13AM +0200, Domenico Cerasuolo wrote:
> > @@ -364,6 +369,9 @@ static void zswap_free_entry(struct zswap_entry *entry)
> >       if (!entry->length)
> >               atomic_dec(&zswap_same_filled_pages);
> >       else {
> > +             spin_lock(&entry->pool->lock);
> > +             list_del_init(&entry->lru);
> > +             spin_unlock(&entry->pool->lock);
>
> This should be list_del(), as the entry is freed right after this and
> the list isn't reused anymore.
>
> The slab memory is recycled, but the allocation site (commented on
> below) doesn't need the list initialized.
>
> However, I think it also needs to check !zpool_evictable(). If
> alloc/store doesn't do the list_add(), this would be a double delete.
>

Thanks Johannes, I'm addressing all of your comments in the series in a V2.

> > @@ -584,14 +592,65 @@ static struct zswap_pool *zswap_pool_find_get(char *type, char *compressor)
> >       return NULL;
> >  }
> >
> > +static int zswap_shrink(struct zswap_pool *pool)
> > +{
> > +     struct zswap_entry *lru_entry, *tree_entry = NULL;
> > +     struct zswap_header *zhdr;
> > +     struct zswap_tree *tree;
> > +     swp_entry_t swpentry;
> > +     int ret;
> > +
> > +     /* get a reclaimable entry from LRU */
> > +     spin_lock(&pool->lock);
> > +     if (list_empty(&pool->lru)) {
> > +             spin_unlock(&pool->lock);
> > +             return -EINVAL;
> > +     }
> > +     lru_entry = list_last_entry(&pool->lru, struct zswap_entry, lru);
> > +     list_del_init(&lru_entry->lru);
> > +     zhdr = zpool_map_handle(pool->zpool, lru_entry->handle, ZPOOL_MM_RO);
> > +     tree = zswap_trees[swp_type(zhdr->swpentry)];
> > +     zpool_unmap_handle(pool->zpool, lru_entry->handle);
> > +     swpentry = zhdr->swpentry;
> > +     spin_unlock(&pool->lock);
>
> Once the pool lock is dropped, the lru_entry might get freed. But the
> swpentry is copied to the stack, and lru_entry isn't deref'd again
> until the entry is verified to still be alive in the tree.
>
> This could use a comment.
>
> > +     /* hold a reference from tree so it won't be freed during writeback */
> > +     spin_lock(&tree->lock);
> > +     tree_entry = zswap_entry_find_get(&tree->rbroot, swp_offset(swpentry));
> > +     if (tree_entry != lru_entry) {
> > +             if (tree_entry)
> > +                     zswap_entry_put(tree, tree_entry);
> > +             spin_unlock(&tree->lock);
> > +             return -EAGAIN;
> > +     }
> > +     spin_unlock(&tree->lock);
>
> It's pretty outrageous how much simpler this is compared to the
> <backend>_reclaim_page() functions! The backends have to jump through
> a lot of hoops to serialize against freeing, whereas zswap can simply
> hold a reference. This is clearly a much better design.
>
> > +     ret = zswap_writeback_entry(pool->zpool, lru_entry->handle);
> > +
> > +     spin_lock(&tree->lock);
> > +     if (ret) {
> > +             spin_lock(&pool->lock);
> > +             list_move(&lru_entry->lru, &pool->lru);
> > +             spin_unlock(&pool->lock);
> > +     }
> > +     zswap_entry_put(tree, tree_entry);
> > +     spin_unlock(&tree->lock);
> > +
> > +     return ret ? -EAGAIN : 0;
> > +}
> > +
> >  static void shrink_worker(struct work_struct *w)
> >  {
> >       struct zswap_pool *pool = container_of(w, typeof(*pool),
> >                                               shrink_work);
> >       int ret, failures = 0;
> >
> > +     /* zpool_evictable will be removed once all 3 backends have migrated*/
>
> Missing space between text and */
>
> >       do {
> > -             ret = zpool_shrink(pool->zpool, 1, NULL);
> > +             if (zpool_evictable(pool->zpool))
> > +                     ret = zpool_shrink(pool->zpool, 1, NULL);
> > +             else
> > +                     ret = zswap_shrink(pool);
> >               if (ret) {
> >                       zswap_reject_reclaim_fail++;
> >                       if (ret != -EAGAIN)
> > @@ -655,6 +714,8 @@ 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->lock);
> >       INIT_WORK(&pool->shrink_work, shrink_worker);
> >
> >       zswap_pool_debug("created", pool);
> > @@ -1270,7 +1331,7 @@ static int zswap_frontswap_store(unsigned type, pgoff_t offset,
> >       }
> >
> >       /* store */
> > -     hlen = zpool_evictable(entry->pool->zpool) ? sizeof(zhdr) : 0;
> > +     hlen = sizeof(zhdr);
> >       gfp = __GFP_NORETRY | __GFP_NOWARN | __GFP_KSWAPD_RECLAIM;
> >       if (zpool_malloc_support_movable(entry->pool->zpool))
> >               gfp |= __GFP_HIGHMEM | __GFP_MOVABLE;
> > @@ -1313,6 +1374,13 @@ static int zswap_frontswap_store(unsigned type, pgoff_t offset,
> >                       zswap_entry_put(tree, dupentry);
> >               }
> >       } while (ret == -EEXIST);
> > +     INIT_LIST_HEAD(&entry->lru);
>
> The list_add() below initializes the entry, so this shouldn't be
> needed.
>
> > +     /* zpool_evictable will be removed once all 3 backends have migrated*/
> > +     if (entry->length && !zpool_evictable(entry->pool->zpool)) {
> > +             spin_lock(&entry->pool->lock);
> > +             list_add(&entry->lru, &entry->pool->lru);
> > +             spin_unlock(&entry->pool->lock);
> > +     }
> >       spin_unlock(&tree->lock);
> >
> >       /* update stats */
Domenico Cerasuolo June 6, 2023, 9:35 a.m. UTC | #4 
On Tue, Jun 6, 2023 at 4:19 AM Yosry Ahmed <yosryahmed@google.com> wrote:
>
> Hi Domenico,
>
> On Mon, Jun 5, 2023 at 1:54 AM Domenico Cerasuolo
> <cerasuolodomenico@gmail.com> wrote:
> >
> > Each zpool driver (zbud, z3fold and zsmalloc) implements its own shrink
> > function, which is called from zpool_shrink. However, with this commit,
> > a unified shrink function is added to zswap. The ultimate goal is to
> > eliminate the need for zpool_shrink once all zpool implementations have
> > dropped their shrink code.
> >
> > To ensure the functionality of each commit, this change focuses solely
> > on adding the mechanism itself. No modifications are made to
> > the backends, meaning that functionally, there are no immediate changes.
> > The zswap mechanism will only come into effect once the backends have
> > removed their shrink code. The subsequent commits will address the
> > modifications needed in the backends.
> >
> > Signed-off-by: Domenico Cerasuolo <cerasuolodomenico@gmail.com>
> > ---
> >  mm/zswap.c | 83 ++++++++++++++++++++++++++++++++++++++++++++++++++----
> >  1 file changed, 78 insertions(+), 5 deletions(-)
> >
> > diff --git a/mm/zswap.c b/mm/zswap.c
> > index bcb82e09eb64..80d7780bf066 100644
> > --- a/mm/zswap.c
> > +++ b/mm/zswap.c
> > @@ -159,6 +159,8 @@ 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 lock;
>
> If this lock is only protecting the lru then I believe it's better to
> call in lru_lock to make it explicit.

Hi Yosry,

thanks for the input, it makes sense to call it lru_lock, will update.

>
> >  };
> >
> >  /*
> > @@ -176,10 +178,12 @@ struct zswap_pool {
> >   *            be held while changing the refcount.  Since the lock must
> >   *            be held, there is no reason to also make refcount atomic.
> >   * length - the length in bytes of the compressed page data.  Needed during
> > - *          decompression. For a same value filled page length is 0.
> > + *          decompression. For a same value filled page length is 0, and both
> > + *          pool and lru are invalid and must be ignored.
> >   * pool - the zswap_pool the entry's data is in
> >   * handle - zpool allocation handle that stores the compressed page data
> >   * value - value of the same-value filled pages which have same content
> > + * lru - handle to the pool's lru used to evict pages.
> >   */
> >  struct zswap_entry {
> >         struct rb_node rbnode;
> > @@ -192,6 +196,7 @@ struct zswap_entry {
> >                 unsigned long value;
> >         };
> >         struct obj_cgroup *objcg;
> > +       struct list_head lru;
> >  };
> >
> >  struct zswap_header {
> > @@ -364,6 +369,9 @@ static void zswap_free_entry(struct zswap_entry *entry)
> >         if (!entry->length)
> >                 atomic_dec(&zswap_same_filled_pages);
> >         else {
> > +               spin_lock(&entry->pool->lock);
> > +               list_del_init(&entry->lru);
> > +               spin_unlock(&entry->pool->lock);
>
> I think we should document the lock ordering somewhere (tree lock ->
> lru lock), otherwise we may run into an ABBA deadlock down the road.

Will update in the next iteration.

>
> >                 zpool_free(entry->pool->zpool, entry->handle);
> >                 zswap_pool_put(entry->pool);
> >         }
> > @@ -584,14 +592,65 @@ static struct zswap_pool *zswap_pool_find_get(char *type, char *compressor)
> >         return NULL;
> >  }
> >
> > +static int zswap_shrink(struct zswap_pool *pool)
> > +{
> > +       struct zswap_entry *lru_entry, *tree_entry = NULL;
> > +       struct zswap_header *zhdr;
> > +       struct zswap_tree *tree;
> > +       swp_entry_t swpentry;
> > +       int ret;
> > +
> > +       /* get a reclaimable entry from LRU */
> > +       spin_lock(&pool->lock);
> > +       if (list_empty(&pool->lru)) {
> > +               spin_unlock(&pool->lock);
> > +               return -EINVAL;
> > +       }
> > +       lru_entry = list_last_entry(&pool->lru, struct zswap_entry, lru);
> > +       list_del_init(&lru_entry->lru);
> > +       zhdr = zpool_map_handle(pool->zpool, lru_entry->handle, ZPOOL_MM_RO);
> > +       tree = zswap_trees[swp_type(zhdr->swpentry)];
> > +       zpool_unmap_handle(pool->zpool, lru_entry->handle);
> > +       swpentry = zhdr->swpentry;
> > +       spin_unlock(&pool->lock);
> > +
> > +       /* hold a reference from tree so it won't be freed during writeback */
> > +       spin_lock(&tree->lock);
> > +       tree_entry = zswap_entry_find_get(&tree->rbroot, swp_offset(swpentry));
> > +       if (tree_entry != lru_entry) {
> > +               if (tree_entry)
> > +                       zswap_entry_put(tree, tree_entry);
> > +               spin_unlock(&tree->lock);
> > +               return -EAGAIN;
> > +       }
> > +       spin_unlock(&tree->lock);
> > +
> > +       ret = zswap_writeback_entry(pool->zpool, lru_entry->handle);
> > +
> > +       spin_lock(&tree->lock);
> > +       if (ret) {
> > +               spin_lock(&pool->lock);
> > +               list_move(&lru_entry->lru, &pool->lru);
> > +               spin_unlock(&pool->lock);
> > +       }
> > +       zswap_entry_put(tree, tree_entry);
> > +       spin_unlock(&tree->lock);
> > +
> > +       return ret ? -EAGAIN : 0;
> > +}
> > +
> >  static void shrink_worker(struct work_struct *w)
> >  {
> >         struct zswap_pool *pool = container_of(w, typeof(*pool),
> >                                                 shrink_work);
> >         int ret, failures = 0;
> >
> > +       /* zpool_evictable will be removed once all 3 backends have migrated*/
> >         do {
> > -               ret = zpool_shrink(pool->zpool, 1, NULL);
> > +               if (zpool_evictable(pool->zpool))
> > +                       ret = zpool_shrink(pool->zpool, 1, NULL);
> > +               else
> > +                       ret = zswap_shrink(pool);
> >                 if (ret) {
> >                         zswap_reject_reclaim_fail++;
> >                         if (ret != -EAGAIN)
> > @@ -655,6 +714,8 @@ 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->lock);
> >         INIT_WORK(&pool->shrink_work, shrink_worker);
> >
> >         zswap_pool_debug("created", pool);
> > @@ -1270,7 +1331,7 @@ static int zswap_frontswap_store(unsigned type, pgoff_t offset,
> >         }
> >
> >         /* store */
> > -       hlen = zpool_evictable(entry->pool->zpool) ? sizeof(zhdr) : 0;
> > +       hlen = sizeof(zhdr);
> >         gfp = __GFP_NORETRY | __GFP_NOWARN | __GFP_KSWAPD_RECLAIM;
> >         if (zpool_malloc_support_movable(entry->pool->zpool))
> >                 gfp |= __GFP_HIGHMEM | __GFP_MOVABLE;
> > @@ -1313,6 +1374,13 @@ static int zswap_frontswap_store(unsigned type, pgoff_t offset,
> >                         zswap_entry_put(tree, dupentry);
> >                 }
> >         } while (ret == -EEXIST);
> > +       INIT_LIST_HEAD(&entry->lru);
> > +       /* zpool_evictable will be removed once all 3 backends have migrated*/
> > +       if (entry->length && !zpool_evictable(entry->pool->zpool)) {
> > +               spin_lock(&entry->pool->lock);
> > +               list_add(&entry->lru, &entry->pool->lru);
> > +               spin_unlock(&entry->pool->lock);
> > +       }
> >         spin_unlock(&tree->lock);
> >
> >         /* update stats */
> > @@ -1384,8 +1452,7 @@ static int zswap_frontswap_load(unsigned type, pgoff_t offset,
> >         /* decompress */
> >         dlen = PAGE_SIZE;
> >         src = zpool_map_handle(entry->pool->zpool, entry->handle, ZPOOL_MM_RO);
> > -       if (zpool_evictable(entry->pool->zpool))
> > -               src += sizeof(struct zswap_header);
> > +       src += sizeof(struct zswap_header);
> >
> >         if (!zpool_can_sleep_mapped(entry->pool->zpool)) {
> >                 memcpy(tmp, src, entry->length);
> > @@ -1415,6 +1482,12 @@ static int zswap_frontswap_load(unsigned type, pgoff_t offset,
> >  freeentry:
> >         spin_lock(&tree->lock);
> >         zswap_entry_put(tree, entry);
> > +       /* zpool_evictable will be removed once all 3 backends have migrated*/
> > +       if (entry->length && !zpool_evictable(entry->pool->zpool)) {
> > +               spin_lock(&entry->pool->lock);
> > +               list_move(&entry->lru, &entry->pool->lru);
> > +               spin_unlock(&entry->pool->lock);
> > +       }
> >         spin_unlock(&tree->lock);
> >
> >         return ret;
> > --
> > 2.34.1
> >
diff mbox series

Patch

diff --git a/mm/zswap.c b/mm/zswap.c
index bcb82e09eb64..80d7780bf066 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -159,6 +159,8 @@  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 lock;
 };
 
 /*
@@ -176,10 +178,12 @@  struct zswap_pool {
  *            be held while changing the refcount.  Since the lock must
  *            be held, there is no reason to also make refcount atomic.
  * length - the length in bytes of the compressed page data.  Needed during
- *          decompression. For a same value filled page length is 0.
+ *          decompression. For a same value filled page length is 0, and both
+ *          pool and lru are invalid and must be ignored.
  * pool - the zswap_pool the entry's data is in
  * handle - zpool allocation handle that stores the compressed page data
  * value - value of the same-value filled pages which have same content
+ * lru - handle to the pool's lru used to evict pages.
  */
 struct zswap_entry {
 	struct rb_node rbnode;
@@ -192,6 +196,7 @@  struct zswap_entry {
 		unsigned long value;
 	};
 	struct obj_cgroup *objcg;
+	struct list_head lru;
 };
 
 struct zswap_header {
@@ -364,6 +369,9 @@  static void zswap_free_entry(struct zswap_entry *entry)
 	if (!entry->length)
 		atomic_dec(&zswap_same_filled_pages);
 	else {
+		spin_lock(&entry->pool->lock);
+		list_del_init(&entry->lru);
+		spin_unlock(&entry->pool->lock);
 		zpool_free(entry->pool->zpool, entry->handle);
 		zswap_pool_put(entry->pool);
 	}
@@ -584,14 +592,65 @@  static struct zswap_pool *zswap_pool_find_get(char *type, char *compressor)
 	return NULL;
 }
 
+static int zswap_shrink(struct zswap_pool *pool)
+{
+	struct zswap_entry *lru_entry, *tree_entry = NULL;
+	struct zswap_header *zhdr;
+	struct zswap_tree *tree;
+	swp_entry_t swpentry;
+	int ret;
+
+	/* get a reclaimable entry from LRU */
+	spin_lock(&pool->lock);
+	if (list_empty(&pool->lru)) {
+		spin_unlock(&pool->lock);
+		return -EINVAL;
+	}
+	lru_entry = list_last_entry(&pool->lru, struct zswap_entry, lru);
+	list_del_init(&lru_entry->lru);
+	zhdr = zpool_map_handle(pool->zpool, lru_entry->handle, ZPOOL_MM_RO);
+	tree = zswap_trees[swp_type(zhdr->swpentry)];
+	zpool_unmap_handle(pool->zpool, lru_entry->handle);
+	swpentry = zhdr->swpentry;
+	spin_unlock(&pool->lock);
+
+	/* hold a reference from tree so it won't be freed during writeback */
+	spin_lock(&tree->lock);
+	tree_entry = zswap_entry_find_get(&tree->rbroot, swp_offset(swpentry));
+	if (tree_entry != lru_entry) {
+		if (tree_entry)
+			zswap_entry_put(tree, tree_entry);
+		spin_unlock(&tree->lock);
+		return -EAGAIN;
+	}
+	spin_unlock(&tree->lock);
+
+	ret = zswap_writeback_entry(pool->zpool, lru_entry->handle);
+
+	spin_lock(&tree->lock);
+	if (ret) {
+		spin_lock(&pool->lock);
+		list_move(&lru_entry->lru, &pool->lru);
+		spin_unlock(&pool->lock);
+	}
+	zswap_entry_put(tree, tree_entry);
+	spin_unlock(&tree->lock);
+
+	return ret ? -EAGAIN : 0;
+}
+
 static void shrink_worker(struct work_struct *w)
 {
 	struct zswap_pool *pool = container_of(w, typeof(*pool),
 						shrink_work);
 	int ret, failures = 0;
 
+	/* zpool_evictable will be removed once all 3 backends have migrated*/
 	do {
-		ret = zpool_shrink(pool->zpool, 1, NULL);
+		if (zpool_evictable(pool->zpool))
+			ret = zpool_shrink(pool->zpool, 1, NULL);
+		else
+			ret = zswap_shrink(pool);
 		if (ret) {
 			zswap_reject_reclaim_fail++;
 			if (ret != -EAGAIN)
@@ -655,6 +714,8 @@  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->lock);
 	INIT_WORK(&pool->shrink_work, shrink_worker);
 
 	zswap_pool_debug("created", pool);
@@ -1270,7 +1331,7 @@  static int zswap_frontswap_store(unsigned type, pgoff_t offset,
 	}
 
 	/* store */
-	hlen = zpool_evictable(entry->pool->zpool) ? sizeof(zhdr) : 0;
+	hlen = sizeof(zhdr);
 	gfp = __GFP_NORETRY | __GFP_NOWARN | __GFP_KSWAPD_RECLAIM;
 	if (zpool_malloc_support_movable(entry->pool->zpool))
 		gfp |= __GFP_HIGHMEM | __GFP_MOVABLE;
@@ -1313,6 +1374,13 @@  static int zswap_frontswap_store(unsigned type, pgoff_t offset,
 			zswap_entry_put(tree, dupentry);
 		}
 	} while (ret == -EEXIST);
+	INIT_LIST_HEAD(&entry->lru);
+	/* zpool_evictable will be removed once all 3 backends have migrated*/
+	if (entry->length && !zpool_evictable(entry->pool->zpool)) {
+		spin_lock(&entry->pool->lock);
+		list_add(&entry->lru, &entry->pool->lru);
+		spin_unlock(&entry->pool->lock);
+	}
 	spin_unlock(&tree->lock);
 
 	/* update stats */
@@ -1384,8 +1452,7 @@  static int zswap_frontswap_load(unsigned type, pgoff_t offset,
 	/* decompress */
 	dlen = PAGE_SIZE;
 	src = zpool_map_handle(entry->pool->zpool, entry->handle, ZPOOL_MM_RO);
-	if (zpool_evictable(entry->pool->zpool))
-		src += sizeof(struct zswap_header);
+	src += sizeof(struct zswap_header);
 
 	if (!zpool_can_sleep_mapped(entry->pool->zpool)) {
 		memcpy(tmp, src, entry->length);
@@ -1415,6 +1482,12 @@  static int zswap_frontswap_load(unsigned type, pgoff_t offset,
 freeentry:
 	spin_lock(&tree->lock);
 	zswap_entry_put(tree, entry);
+	/* zpool_evictable will be removed once all 3 backends have migrated*/
+	if (entry->length && !zpool_evictable(entry->pool->zpool)) {
+		spin_lock(&entry->pool->lock);
+		list_move(&entry->lru, &entry->pool->lru);
+		spin_unlock(&entry->pool->lock);
+	}
 	spin_unlock(&tree->lock);
 
 	return ret;