On Mon, Jan 29, 2024 at 5:42 PM Johannes Weiner <hannes@cmpxchg.org> wrote:
>
> Shrinking needs writeback. Naturally, move the writeback code above
> the shrinking code. Delete the forward decl.
Honestly, do we even need a separate section haha. Writeback and
shrink are used interchangeably in my head - they're the same
category.
>
> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Anyway:
Reviewed-by: Nhat Pham <nphamcs@gmail.com>
@@ -276,9 +276,6 @@ static inline struct zswap_tree *swap_zswap_tree(swp_entry_t swp)
pr_debug("%s pool %s/%s\n", msg, (p)->tfm_name, \
zpool_get_type((p)->zpools[0]))
-static int zswap_writeback_entry(struct zswap_entry *entry,
- swp_entry_t swpentry);
-
static bool zswap_is_full(void)
{
return totalram_pages() * zswap_max_pool_percent / 100 <
@@ -1163,6 +1160,96 @@ static void zswap_decompress(struct zswap_entry *entry, struct page *page)
zpool_unmap_handle(zpool, entry->handle);
}
+/*********************************
+* writeback code
+**********************************/
+/*
+ * Attempts to free an entry by adding a folio to the swap cache,
+ * decompressing the entry data into the folio, and issuing a
+ * bio write to write the folio back to the swap device.
+ *
+ * This can be thought of as a "resumed writeback" of the folio
+ * to the swap device. We are basically resuming the same swap
+ * writeback path that was intercepted with the zswap_store()
+ * in the first place. After the folio has been decompressed into
+ * the swap cache, the compressed version stored by zswap can be
+ * freed.
+ */
+static int zswap_writeback_entry(struct zswap_entry *entry,
+ swp_entry_t swpentry)
+{
+ struct zswap_tree *tree;
+ struct folio *folio;
+ struct mempolicy *mpol;
+ bool folio_was_allocated;
+ struct writeback_control wbc = {
+ .sync_mode = WB_SYNC_NONE,
+ };
+
+ /* try to allocate swap cache folio */
+ mpol = get_task_policy(current);
+ folio = __read_swap_cache_async(swpentry, GFP_KERNEL, mpol,
+ NO_INTERLEAVE_INDEX, &folio_was_allocated, true);
+ if (!folio)
+ return -ENOMEM;
+
+ /*
+ * Found an existing folio, we raced with swapin or concurrent
+ * shrinker. We generally writeback cold folios from zswap, and
+ * swapin means the folio just became hot, so skip this folio.
+ * For unlikely concurrent shrinker case, it will be unlinked
+ * and freed when invalidated by the concurrent shrinker anyway.
+ */
+ if (!folio_was_allocated) {
+ folio_put(folio);
+ return -EEXIST;
+ }
+
+ /*
+ * folio is locked, and the swapcache is now secured against
+ * concurrent swapping to and from the slot. Verify that the
+ * swap entry hasn't been invalidated and recycled behind our
+ * backs (our zswap_entry reference doesn't prevent that), to
+ * avoid overwriting a new swap folio with old compressed data.
+ */
+ tree = swap_zswap_tree(swpentry);
+ spin_lock(&tree->lock);
+ if (zswap_rb_search(&tree->rbroot, swp_offset(swpentry)) != entry) {
+ spin_unlock(&tree->lock);
+ delete_from_swap_cache(folio);
+ folio_unlock(folio);
+ folio_put(folio);
+ return -ENOMEM;
+ }
+
+ /* Safe to deref entry after the entry is verified above. */
+ zswap_entry_get(entry);
+ spin_unlock(&tree->lock);
+
+ zswap_decompress(entry, &folio->page);
+
+ count_vm_event(ZSWPWB);
+ if (entry->objcg)
+ count_objcg_event(entry->objcg, ZSWPWB);
+
+ spin_lock(&tree->lock);
+ zswap_invalidate_entry(tree, entry);
+ zswap_entry_put(entry);
+ spin_unlock(&tree->lock);
+
+ /* folio is up to date */
+ folio_mark_uptodate(folio);
+
+ /* move it to the tail of the inactive list after end_writeback */
+ folio_set_reclaim(folio);
+
+ /* start writeback */
+ __swap_writepage(folio, &wbc);
+ folio_put(folio);
+
+ return 0;
+}
+
/*********************************
* shrinker functions
**********************************/
@@ -1419,96 +1506,6 @@ static void shrink_worker(struct work_struct *w)
zswap_pool_put(pool);
}
-/*********************************
-* writeback code
-**********************************/
-/*
- * Attempts to free an entry by adding a folio to the swap cache,
- * decompressing the entry data into the folio, and issuing a
- * bio write to write the folio back to the swap device.
- *
- * This can be thought of as a "resumed writeback" of the folio
- * to the swap device. We are basically resuming the same swap
- * writeback path that was intercepted with the zswap_store()
- * in the first place. After the folio has been decompressed into
- * the swap cache, the compressed version stored by zswap can be
- * freed.
- */
-static int zswap_writeback_entry(struct zswap_entry *entry,
- swp_entry_t swpentry)
-{
- struct zswap_tree *tree;
- struct folio *folio;
- struct mempolicy *mpol;
- bool folio_was_allocated;
- struct writeback_control wbc = {
- .sync_mode = WB_SYNC_NONE,
- };
-
- /* try to allocate swap cache folio */
- mpol = get_task_policy(current);
- folio = __read_swap_cache_async(swpentry, GFP_KERNEL, mpol,
- NO_INTERLEAVE_INDEX, &folio_was_allocated, true);
- if (!folio)
- return -ENOMEM;
-
- /*
- * Found an existing folio, we raced with swapin or concurrent
- * shrinker. We generally writeback cold folios from zswap, and
- * swapin means the folio just became hot, so skip this folio.
- * For unlikely concurrent shrinker case, it will be unlinked
- * and freed when invalidated by the concurrent shrinker anyway.
- */
- if (!folio_was_allocated) {
- folio_put(folio);
- return -EEXIST;
- }
-
- /*
- * folio is locked, and the swapcache is now secured against
- * concurrent swapping to and from the slot. Verify that the
- * swap entry hasn't been invalidated and recycled behind our
- * backs (our zswap_entry reference doesn't prevent that), to
- * avoid overwriting a new swap folio with old compressed data.
- */
- tree = swap_zswap_tree(swpentry);
- spin_lock(&tree->lock);
- if (zswap_rb_search(&tree->rbroot, swp_offset(swpentry)) != entry) {
- spin_unlock(&tree->lock);
- delete_from_swap_cache(folio);
- folio_unlock(folio);
- folio_put(folio);
- return -ENOMEM;
- }
-
- /* Safe to deref entry after the entry is verified above. */
- zswap_entry_get(entry);
- spin_unlock(&tree->lock);
-
- zswap_decompress(entry, &folio->page);
-
- count_vm_event(ZSWPWB);
- if (entry->objcg)
- count_objcg_event(entry->objcg, ZSWPWB);
-
- spin_lock(&tree->lock);
- zswap_invalidate_entry(tree, entry);
- zswap_entry_put(entry);
- spin_unlock(&tree->lock);
-
- /* folio is up to date */
- folio_mark_uptodate(folio);
-
- /* move it to the tail of the inactive list after end_writeback */
- folio_set_reclaim(folio);
-
- /* start writeback */
- __swap_writepage(folio, &wbc);
- folio_put(folio);
-
- return 0;
-}
-
static int zswap_is_page_same_filled(void *ptr, unsigned long *value)
{
unsigned long *page;