[PATCH v2 1/4] mm: change to return bool for folio_isolate_lru()

[Baolin Wang]

Now the folio_isolate_lru() did not return a boolean value to indicate
isolation success or not, however below code checking the return value
can make people think that it was a boolean success/failure thing, which
makes people easy to make mistakes (see the fix patch[1]).

if (folio_isolate_lru(folio))
	continue;

Thus it's better to check the negative error value expilictly returned by
folio_isolate_lru(), which makes code more clear per Linus's suggestion[2].
Moreover Matthew suggested we can convert the isolation functions to return
a boolean[3], since most users did not care about the negative error value,
and can also remove the confusing of checking return value.

So this patch converts the folio_isolate_lru() to return a boolean value,
which means return 'true' to indicate the folio isolation is successful, and
'false' means a failure to isolation. Meanwhile changing all users' logic of
checking the isolation state.

No functional changes intended.

[1] https://lore.kernel.org/all/20230131063206.28820-1-Kuan-Ying.Lee@xxxxxxxxxxxx/T/#u
[2] https://lore.kernel.org/all/CAHk-=wiBrY+O-4=2mrbVyxR+hOqfdJ=Do6xoucfJ9_5az01L4Q@xxxxxxxxxxxxxx/
[3] https://lore.kernel.org/all/Y+sTFqwMNAjDvxw3@xxxxxxxxxxxxxxxxxxxx/

Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
---
 mm/damon/paddr.c  |  2 +-
 mm/folio-compat.c |  8 +++++++-
 mm/gup.c          |  2 +-
 mm/internal.h     |  2 +-
 mm/khugepaged.c   |  2 +-
 mm/madvise.c      |  4 ++--
 mm/mempolicy.c    |  2 +-
 mm/vmscan.c       | 10 +++++-----
 8 files changed, 19 insertions(+), 13 deletions(-)

diff --git a/mm/damon/paddr.c b/mm/damon/paddr.c
index b4df9b9bcc0a..607bb69e526c 100644
--- a/mm/damon/paddr.c
+++ b/mm/damon/paddr.c
@@ -246,7 +246,7 @@ static unsigned long damon_pa_pageout(struct damon_region *r, struct damos *s)
 
 		folio_clear_referenced(folio);
 		folio_test_clear_young(folio);
-		if (folio_isolate_lru(folio)) {
+		if (!folio_isolate_lru(folio)) {
 			folio_put(folio);
 			continue;
 		}
diff --git a/mm/folio-compat.c b/mm/folio-compat.c
index 18c48b557926..540373cf904e 100644
--- a/mm/folio-compat.c
+++ b/mm/folio-compat.c
@@ -115,9 +115,15 @@ EXPORT_SYMBOL(grab_cache_page_write_begin);
 
 int isolate_lru_page(struct page *page)
 {
+	bool ret;
+
 	if (WARN_RATELIMIT(PageTail(page), "trying to isolate tail page"))
 		return -EBUSY;
-	return folio_isolate_lru((struct folio *)page);
+	ret = folio_isolate_lru((struct folio *)page);
+	if (ret)
+		return 0;
+
+	return -EBUSY;
 }
 
 void putback_lru_page(struct page *page)
diff --git a/mm/gup.c b/mm/gup.c
index b0885f70579c..eab18ba045db 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1939,7 +1939,7 @@ static unsigned long collect_longterm_unpinnable_pages(
 			drain_allow = false;
 		}
 
-		if (folio_isolate_lru(folio))
+		if (!folio_isolate_lru(folio))
 			continue;
 
 		list_add_tail(&folio->lru, movable_page_list);
diff --git a/mm/internal.h b/mm/internal.h
index dfb37e94e140..8645e8496537 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -188,7 +188,7 @@ pgprot_t __init early_memremap_pgprot_adjust(resource_size_t phys_addr,
  * in mm/vmscan.c:
  */
 int isolate_lru_page(struct page *page);
-int folio_isolate_lru(struct folio *folio);
+bool folio_isolate_lru(struct folio *folio);
 void putback_lru_page(struct page *page);
 void folio_putback_lru(struct folio *folio);
 extern void reclaim_throttle(pg_data_t *pgdat, enum vmscan_throttle_state reason);
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index a5d32231bfad..cee659cfa3c1 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -2047,7 +2047,7 @@ static int collapse_file(struct mm_struct *mm, unsigned long addr,
 			goto out_unlock;
 		}
 
-		if (folio_isolate_lru(folio)) {
+		if (!folio_isolate_lru(folio)) {
 			result = SCAN_DEL_PAGE_LRU;
 			goto out_unlock;
 		}
diff --git a/mm/madvise.c b/mm/madvise.c
index 5a5a687d03c2..c2202f51e9dd 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -406,7 +406,7 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd,
 		folio_clear_referenced(folio);
 		folio_test_clear_young(folio);
 		if (pageout) {
-			if (!folio_isolate_lru(folio)) {
+			if (folio_isolate_lru(folio)) {
 				if (folio_test_unevictable(folio))
 					folio_putback_lru(folio);
 				else
@@ -500,7 +500,7 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd,
 		folio_clear_referenced(folio);
 		folio_test_clear_young(folio);
 		if (pageout) {
-			if (!folio_isolate_lru(folio)) {
+			if (folio_isolate_lru(folio)) {
 				if (folio_test_unevictable(folio))
 					folio_putback_lru(folio);
 				else
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 0919c7a719d4..2751bc3310fd 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -1033,7 +1033,7 @@ static int migrate_folio_add(struct folio *folio, struct list_head *foliolist,
 	 * expensive, so check the estimated mapcount of the folio instead.
 	 */
 	if ((flags & MPOL_MF_MOVE_ALL) || folio_estimated_sharers(folio) == 1) {
-		if (!folio_isolate_lru(folio)) {
+		if (folio_isolate_lru(folio)) {
 			list_add_tail(&folio->lru, foliolist);
 			node_stat_mod_folio(folio,
 				NR_ISOLATED_ANON + folio_is_file_lru(folio),
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 34535bbd4fe9..7658b40df947 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2337,12 +2337,12 @@ static unsigned long isolate_lru_folios(unsigned long nr_to_scan,
  * (2) The lru_lock must not be held.
  * (3) Interrupts must be enabled.
  *
- * Return: 0 if the folio was removed from an LRU list.
- * -EBUSY if the folio was not on an LRU list.
+ * Return: true if the folio was removed from an LRU list.
+ * false if the folio was not on an LRU list.
  */
-int folio_isolate_lru(struct folio *folio)
+bool folio_isolate_lru(struct folio *folio)
 {
-	int ret = -EBUSY;
+	bool ret = false;
 
 	VM_BUG_ON_FOLIO(!folio_ref_count(folio), folio);
 
@@ -2353,7 +2353,7 @@ int folio_isolate_lru(struct folio *folio)
 		lruvec = folio_lruvec_lock_irq(folio);
 		lruvec_del_folio(lruvec, folio);
 		unlock_page_lruvec_irq(lruvec);
-		ret = 0;
+		ret = true;
 	}
 
 	return ret;
-- 
2.27.0