mm: change to return bool for folio_isolate_lru()

Patch series "Change the return value for page isolation functions", v3.

Now the page isolation functions did not return a boolean to indicate
success or not, instead it will return a negative error when failed
to isolate a page. So below code used in most places seem a boolean
success/failure thing, which can confuse people whether the isolation
is successful.

if (folio_isolate_lru(folio))
        continue;

Moreover the page isolation functions only return 0 or -EBUSY, and
most users did not care about the negative error except for few users,
thus we can convert all page isolation functions to return a boolean
value, which can remove the confusion to make code more clear.

No functional changes intended in this patch series.


This patch (of 4):

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/[email protected]/T/#u
[2] https://lore.kernel.org/all/CAHk-=wiBrY+O-4=2mrbVyxR+hOqfdJ=Do6xoucfJ9_5az01L4Q@mail.gmail.com/
[3] https://lore.kernel.org/all/[email protected]/

Link: https://lkml.kernel.org/r/[email protected]
Link: https://lkml.kernel.org/r/8a4e3679ed4196168efadf7ea36c038f2f7d5aa9.1676424378.git.baolin.wang@linux.alibaba.com
Signed-off-by: Baolin Wang <[email protected]>
Reviewed-by: SeongJae Park <[email protected]>
Acked-by: David Hildenbrand <[email protected]>
Reviewed-by: Matthew Wilcox (Oracle) <[email protected]>
Acked-by: Linus Torvalds <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Miaohe Lin <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Mike Kravetz <[email protected]>
Cc: Muchun Song <[email protected]>
Cc: Naoya Horiguchi <[email protected]>
Cc: Oscar Salvador <[email protected]>
Cc: Roman Gushchin <[email protected]>
Cc: Shakeel Butt <[email protected]>

Signed-off-by: Andrew Morton <[email protected]>

Author: Baolin Wang

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;
 		}

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)

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);

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);

mm/khugepaged.c

@@ -1950,7 +1950,7 @@ 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;
 		}

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

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),

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;