[PATCH v5 2/5] mm/vmscan: extract folio_free() from shrink_folio_list()

[Zhang Peng <zippermonkey@icloud.com>]

shrink_folio_list() contains a self-contained folio-freeing section:
buffer release, lazyfree, __remove_mapping, and folio_batch drain.
Extract it into folio_free() to reduce the size of shrink_folio_list()
and make the freeing step independently readable.

No functional change.

Signed-off-by: Zhang Peng <bruzzhang@tencent.com>
---
 mm/vmscan.c | 164 +++++++++++++++++++++++++++++++++---------------------------
 1 file changed, 89 insertions(+), 75 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 5ba880dce21e..a0807dd01c5a 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1076,6 +1076,93 @@ static void folio_activate_locked(struct folio *folio,
 	}
 }
 
+static bool folio_try_reclaim_free(struct folio *folio,
+		struct folio_batch *free_folios,
+		struct scan_control *sc, struct reclaim_stat *stat,
+		unsigned int *nr_reclaimed)
+{
+	const unsigned int nr_pages = folio_nr_pages(folio);
+	struct address_space *mapping = folio_mapping(folio);
+
+	/*
+	 * If the folio has buffers, try to free the buffer mappings
+	 * associated with this folio. If we succeed we try to free
+	 * the folio as well.
+	 *
+	 * We do this even if the folio is dirty.
+	 * filemap_release_folio() does not perform I/O, but it is
+	 * possible for a folio to have the dirty flag set, but it
+	 * is actually clean (all its buffers are clean).  This
+	 * happens if the buffers were written out directly, with
+	 * submit_bh(). ext3 will do this, as well as the blockdev
+	 * mapping.  filemap_release_folio() will discover that
+	 * cleanness and will drop the buffers and mark the folio
+	 * clean - it can be freed.
+	 *
+	 * Rarely, folios can have buffers and no ->mapping.  These
+	 * are the folios which were not successfully invalidated in
+	 * truncate_cleanup_folio().  We try to drop those buffers
+	 * here and if that worked, and the folio is no longer
+	 * mapped into process address space (refcount == 1) it can
+	 * be freed.  Otherwise, leave the folio on the LRU so it is
+	 * swappable.
+	 */
+	if (folio_needs_release(folio)) {
+		if (!filemap_release_folio(folio, sc->gfp_mask)) {
+			folio_activate_locked(folio, stat);
+			return false;
+		}
+
+		if (!mapping && folio_ref_count(folio) == 1) {
+			folio_unlock(folio);
+			if (folio_put_testzero(folio))
+				goto free_it;
+			else {
+				/*
+				 * rare race with speculative reference.
+				 * the speculative reference will free
+				 * this folio shortly, so we may
+				 * increment nr_reclaimed here (and
+				 * leave it off the LRU).
+				 */
+				*nr_reclaimed += nr_pages;
+				return true;
+			}
+		}
+	}
+
+	if (folio_test_lazyfree(folio)) {
+		/* follow __remove_mapping for reference */
+		if (!folio_ref_freeze(folio, 1))
+			return false;
+		/*
+		 * The folio has only one reference left, which is
+		 * from the isolation. After the caller puts the
+		 * folio back on the lru and drops the reference, the
+		 * folio will be freed anyway. It doesn't matter
+		 * which lru it goes on. So we don't bother checking
+		 * the dirty flag here.
+		 */
+		count_vm_events(PGLAZYFREED, nr_pages);
+		count_memcg_folio_events(folio, PGLAZYFREED, nr_pages);
+	} else if (!mapping || !__remove_mapping(mapping, folio, true,
+							sc->target_mem_cgroup))
+		return false;
+
+	folio_unlock(folio);
+free_it:
+	VM_WARN_ON_ONCE_FOLIO(folio_ref_count(folio), folio);
+	*nr_reclaimed += nr_pages;
+
+	folio_unqueue_deferred_split(folio);
+	if (folio_batch_add(free_folios, folio) == 0) {
+		mem_cgroup_uncharge_folios(free_folios);
+		try_to_unmap_flush();
+		free_unref_folios(free_folios);
+	}
+	return true;
+}
+
 /*
  * shrink_folio_list() returns the number of reclaimed pages
  */
@@ -1463,82 +1550,9 @@ static unsigned int shrink_folio_list(struct list_head *folio_list,
 			}
 		}
 
-		/*
-		 * If the folio has buffers, try to free the buffer
-		 * mappings associated with this folio. If we succeed
-		 * we try to free the folio as well.
-		 *
-		 * We do this even if the folio is dirty.
-		 * filemap_release_folio() does not perform I/O, but it
-		 * is possible for a folio to have the dirty flag set,
-		 * but it is actually clean (all its buffers are clean).
-		 * This happens if the buffers were written out directly,
-		 * with submit_bh(). ext3 will do this, as well as
-		 * the blockdev mapping.  filemap_release_folio() will
-		 * discover that cleanness and will drop the buffers
-		 * and mark the folio clean - it can be freed.
-		 *
-		 * Rarely, folios can have buffers and no ->mapping.
-		 * These are the folios which were not successfully
-		 * invalidated in truncate_cleanup_folio().  We try to
-		 * drop those buffers here and if that worked, and the
-		 * folio is no longer mapped into process address space
-		 * (refcount == 1) it can be freed.  Otherwise, leave
-		 * the folio on the LRU so it is swappable.
-		 */
-		if (folio_needs_release(folio)) {
-			if (!filemap_release_folio(folio, sc->gfp_mask))
-				goto activate_locked;
-			if (!mapping && folio_ref_count(folio) == 1) {
-				folio_unlock(folio);
-				if (folio_put_testzero(folio))
-					goto free_it;
-				else {
-					/*
-					 * rare race with speculative reference.
-					 * the speculative reference will free
-					 * this folio shortly, so we may
-					 * increment nr_reclaimed here (and
-					 * leave it off the LRU).
-					 */
-					nr_reclaimed += nr_pages;
-					continue;
-				}
-			}
-		}
-
-		if (folio_test_lazyfree(folio)) {
-			/* follow __remove_mapping for reference */
-			if (!folio_ref_freeze(folio, 1))
-				goto keep_locked;
-			/*
-			 * The folio has only one reference left, which is
-			 * from the isolation. After the caller puts the
-			 * folio back on the lru and drops the reference, the
-			 * folio will be freed anyway. It doesn't matter
-			 * which lru it goes on. So we don't bother checking
-			 * the dirty flag here.
-			 */
-			count_vm_events(PGLAZYFREED, nr_pages);
-			count_memcg_folio_events(folio, PGLAZYFREED, nr_pages);
-		} else if (!mapping || !__remove_mapping(mapping, folio, true,
-							 sc->target_mem_cgroup))
+		if (!folio_try_reclaim_free(folio, &free_folios, sc, stat,
+					   &nr_reclaimed))
 			goto keep_locked;
-
-		folio_unlock(folio);
-free_it:
-		/*
-		 * Folio may get swapped out as a whole, need to account
-		 * all pages in it.
-		 */
-		nr_reclaimed += nr_pages;
-
-		folio_unqueue_deferred_split(folio);
-		if (folio_batch_add(&free_folios, folio) == 0) {
-			mem_cgroup_uncharge_folios(&free_folios);
-			try_to_unmap_flush();
-			free_unref_folios(&free_folios);
-		}
 		continue;
 
 activate_locked_split:

-- 
2.43.7