mm/zswap: cleanup zswap_writeback_entry()

Also after the common decompress part goes to __zswap_load(), we can
cleanup the zswap_writeback_entry() a little.

Link: https://lkml.kernel.org/r/20231213-zswap-dstmem-v5-4-9382162bbf05@bytedance.com
Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>
Reviewed-by: Yosry Ahmed <yosryahmed@google.com>
Reviewed-by: Nhat Pham <nphamcs@gmail.com>
Acked-by: Chris Li <chrisl@kernel.org> (Google)
Cc: Barry Song <21cnbao@gmail.com>
Cc: Dan Streetman <ddstreet@ieee.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Seth Jennings <sjenning@redhat.com>
Cc: Vitaly Wool <vitaly.wool@konsulko.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/zswap.c b/mm/zswap.c
index d8e883b52cb7cf12744b17206f02c12eb5fbbc96..880c33bbe1466eae8bcdcace0d968ff91a169ebc 100644 (file)
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -1434,7 +1434,6 @@ static int zswap_writeback_entry(struct zswap_entry *entry,
        struct page *page;
        struct mempolicy *mpol;
        bool page_was_allocated;
-       int ret;
        struct writeback_control wbc = {
                .sync_mode = WB_SYNC_NONE,
        };
@@ -1443,16 +1442,17 @@ static int zswap_writeback_entry(struct zswap_entry *entry,
        mpol = get_task_policy(current);
        page = __read_swap_cache_async(swpentry, GFP_KERNEL, mpol,
                                NO_INTERLEAVE_INDEX, &page_was_allocated, true);
-       if (!page) {
-               ret = -ENOMEM;
-               goto fail;
-       }
+       if (!page)
+               return -ENOMEM;
 
-       /* Found an existing page, we raced with load/swapin */
+       /*
+        * Found an existing page, we raced with load/swapin. We generally
+        * writeback cold pages from zswap, and swapin means the page just
+        * became hot. Skip this page and let the caller find another one.
+        */
        if (!page_was_allocated) {
                put_page(page);
-               ret = -EEXIST;
-               goto fail;
+               return -EEXIST;
        }
 
        /*
@@ -1466,8 +1466,7 @@ static int zswap_writeback_entry(struct zswap_entry *entry,
        if (zswap_rb_search(&tree->rbroot, swp_offset(entry->swpentry)) != entry) {
                spin_unlock(&tree->lock);
                delete_from_swap_cache(page_folio(page));
-               ret = -ENOMEM;
-               goto fail;
+               return -ENOMEM;
        }
        spin_unlock(&tree->lock);
 
@@ -1483,15 +1482,7 @@ static int zswap_writeback_entry(struct zswap_entry *entry,
        __swap_writepage(page, &wbc);
        put_page(page);
 
-       return ret;
-
-fail:
-       /*
-        * If we get here because the page is already in swapcache, a
-        * load may be happening concurrently. It is safe and okay to
-        * not free the entry. It is also okay to return !0.
-        */
-       return ret;
+       return 0;
 }
 
 static int zswap_is_page_same_filled(void *ptr, unsigned long *value)