mm: vmscan: simplify the folio refcount check in pageout()

Since we no longer attempt to write back filesystem folios in pageout()
(they will be filtered out by the following check in pageout()), and only
tmpfs/shmem folios and anonymous swapcache folios can be written back, we
can remove the redundant folio_test_private() when checking the folio's
refcount, as tmpfs/shmem and swapcache folios do not use the PG_private
flag.

While we're at it, we can open-code the folio refcount check instead of
adding a simple helper that has only one user.

Link: https://lkml.kernel.org/r/4cbbec5bb92397aa4597105f1f499aabf7a1901c.1758166683.git.baolin.wang@linux.alibaba.com
Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Acked-by: David Hildenbrand <david@redhat.com>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Hugh Dickins <hughd@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Qi Zheng <zhengqi.arch@bytedance.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 0684da19aa64eef0c2f38b2b58296912857d3d38..51ffd32e6e019b43ffd60cc9424b0b4e89fb3e8f 100644 (file)
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -477,17 +477,6 @@ static int reclaimer_offset(struct scan_control *sc)
        return PGSTEAL_DIRECT - PGSTEAL_KSWAPD;
 }
 
-static inline int is_page_cache_freeable(struct folio *folio)
-{
-       /*
-        * A freeable page cache folio is referenced only by the caller
-        * that isolated the folio, the page cache and optional filesystem
-        * private data at folio->private.
-        */
-       return folio_ref_count(folio) - folio_test_private(folio) ==
-               1 + folio_nr_pages(folio);
-}
-
 /*
  * We detected a synchronous write error writing a folio out.  Probably
  * -ENOSPC.  We need to propagate that into the address_space for a subsequent
@@ -696,8 +685,11 @@ static pageout_t pageout(struct folio *folio, struct address_space *mapping,
         * block, for some throttling. This happens by accident, because
         * swap_backing_dev_info is bust: it doesn't reflect the
         * congestion state of the swapdevs.  Easy to fix, if needed.
+        *
+        * A freeable shmem or swapcache folio is referenced only by the
+        * caller that isolated the folio and the page cache.
         */
-       if (!is_page_cache_freeable(folio) || !mapping)
+       if (folio_ref_count(folio) != 1 + folio_nr_pages(folio) || !mapping)
                return PAGE_KEEP;
        if (!shmem_mapping(mapping) && !folio_test_anon(folio))
                return PAGE_ACTIVATE;