[PATCH v4 4/5] mm/vmscan: extract folio unmap logic into folio_try_unmap()

[Zhang Peng <zippermonkey@icloud.com>]

shrink_folio_list() contains a self-contained block that sets up
TTU flags and calls try_to_unmap(), accounting for failures via
reclaim_stat. Extract it into folio_try_unmap() to reduce the size
of shrink_folio_list() and make the unmap step independently readable.

folio_try_unmap() is only called when the folio is actually mapped;
the !folio_mapped() check stays in the caller, keeping the function's
semantics clear: it tries to unmap a mapped folio and returns whether
the unmap succeeded.

No functional change.

Signed-off-by: Zhang Peng <bruzzhang@tencent.com>
---
 mm/vmscan.c | 68 ++++++++++++++++++++++++++++++++++---------------------------
 1 file changed, 38 insertions(+), 30 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 456d38eb172c..abf3a2878456 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1221,6 +1221,41 @@ static bool pageout_one(struct folio *folio,
 	return false;
 }
 
+static bool folio_try_unmap(struct folio *folio, struct reclaim_stat *stat,
+			    unsigned int nr_pages)
+{
+	enum ttu_flags flags = TTU_BATCH_FLUSH;
+	bool was_swapbacked;
+
+	was_swapbacked = folio_test_swapbacked(folio);
+	if (folio_test_pmd_mappable(folio))
+		flags |= TTU_SPLIT_HUGE_PMD;
+	/*
+	 * Without TTU_SYNC, try_to_unmap will only begin to
+	 * hold PTL from the first present PTE within a large
+	 * folio. Some initial PTEs might be skipped due to
+	 * races with parallel PTE writes in which PTEs can be
+	 * cleared temporarily before being written new present
+	 * values. This will lead to a large folio is still
+	 * mapped while some subpages have been partially
+	 * unmapped after try_to_unmap; TTU_SYNC helps
+	 * try_to_unmap acquire PTL from the first PTE,
+	 * eliminating the influence of temporary PTE values.
+	 */
+	if (folio_test_large(folio))
+		flags |= TTU_SYNC;
+
+	try_to_unmap(folio, flags);
+	if (folio_mapped(folio)) {
+		stat->nr_unmap_fail += nr_pages;
+		if (!was_swapbacked &&
+		    folio_test_swapbacked(folio))
+			stat->nr_lazyfree_fail += nr_pages;
+		return false;
+	}
+	return true;
+}
+
 /*
  * Reclaimed folios are counted in the return value.
  */
@@ -1495,36 +1530,9 @@ static unsigned int shrink_folio_list(struct list_head *folio_list,
 		 * The folio is mapped into the page tables of one or more
 		 * processes. Try to unmap it here.
 		 */
-		if (folio_mapped(folio)) {
-			enum ttu_flags flags = TTU_BATCH_FLUSH;
-			bool was_swapbacked = folio_test_swapbacked(folio);
-
-			if (folio_test_pmd_mappable(folio))
-				flags |= TTU_SPLIT_HUGE_PMD;
-			/*
-			 * Without TTU_SYNC, try_to_unmap will only begin to
-			 * hold PTL from the first present PTE within a large
-			 * folio. Some initial PTEs might be skipped due to
-			 * races with parallel PTE writes in which PTEs can be
-			 * cleared temporarily before being written new present
-			 * values. This will lead to a large folio is still
-			 * mapped while some subpages have been partially
-			 * unmapped after try_to_unmap; TTU_SYNC helps
-			 * try_to_unmap acquire PTL from the first PTE,
-			 * eliminating the influence of temporary PTE values.
-			 */
-			if (folio_test_large(folio))
-				flags |= TTU_SYNC;
-
-			try_to_unmap(folio, flags);
-			if (folio_mapped(folio)) {
-				stat->nr_unmap_fail += nr_pages;
-				if (!was_swapbacked &&
-				    folio_test_swapbacked(folio))
-					stat->nr_lazyfree_fail += nr_pages;
-				goto activate_locked;
-			}
-		}
+		if (folio_mapped(folio) &&
+		    !folio_try_unmap(folio, stat, nr_pages))
+			goto activate_locked;
 
 		/*
 		 * Folio is unmapped now so it cannot be newly pinned anymore.

-- 
2.43.7