mm/vmscan: convert isolate_lru_pages() to use a folio

Remove a few hidden calls to compound_head, saving 279 bytes of text.

Link: https://lkml.kernel.org/r/20220617154248.700416-3-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/vmscan.c

@@ -160,17 +160,17 @@ struct scan_control {
 };
 
 #ifdef ARCH_HAS_PREFETCHW
-#define prefetchw_prev_lru_page(_page, _base, _field)			\
+#define prefetchw_prev_lru_folio(_folio, _base, _field)			\
 	do {								\
-		if ((_page)->lru.prev != _base) {			\
-			struct page *prev;				\
+		if ((_folio)->lru.prev != _base) {			\
+			struct folio *prev;				\
 									\
-			prev = lru_to_page(&(_page->lru));		\
+			prev = lru_to_folio(&(_folio->lru));		\
 			prefetchw(&prev->_field);			\
 		}							\
 	} while (0)
 #else
-#define prefetchw_prev_lru_page(_page, _base, _field) do { } while (0)
+#define prefetchw_prev_lru_folio(_folio, _base, _field) do { } while (0)
 #endif
 
 /*
@@ -2139,72 +2139,72 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
 	unsigned long nr_skipped[MAX_NR_ZONES] = { 0, };
 	unsigned long skipped = 0;
 	unsigned long scan, total_scan, nr_pages;
-	LIST_HEAD(pages_skipped);
+	LIST_HEAD(folios_skipped);
 
 	total_scan = 0;
 	scan = 0;
 	while (scan < nr_to_scan && !list_empty(src)) {
 		struct list_head *move_to = src;
-		struct page *page;
+		struct folio *folio;
 
-		page = lru_to_page(src);
-		prefetchw_prev_lru_page(page, src, flags);
+		folio = lru_to_folio(src);
+		prefetchw_prev_lru_folio(folio, src, flags);
 
-		nr_pages = compound_nr(page);
+		nr_pages = folio_nr_pages(folio);
 		total_scan += nr_pages;
 
-		if (page_zonenum(page) > sc->reclaim_idx) {
-			nr_skipped[page_zonenum(page)] += nr_pages;
-			move_to = &pages_skipped;
+		if (folio_zonenum(folio) > sc->reclaim_idx) {
+			nr_skipped[folio_zonenum(folio)] += nr_pages;
+			move_to = &folios_skipped;
 			goto move;
 		}
 
 		/*
-		 * Do not count skipped pages because that makes the function
-		 * return with no isolated pages if the LRU mostly contains
-		 * ineligible pages.  This causes the VM to not reclaim any
-		 * pages, triggering a premature OOM.
-		 * Account all tail pages of THP.
+		 * Do not count skipped folios because that makes the function
+		 * return with no isolated folios if the LRU mostly contains
+		 * ineligible folios.  This causes the VM to not reclaim any
+		 * folios, triggering a premature OOM.
+		 * Account all pages in a folio.
 		 */
 		scan += nr_pages;
 
-		if (!PageLRU(page))
+		if (!folio_test_lru(folio))
 			goto move;
-		if (!sc->may_unmap && page_mapped(page))
+		if (!sc->may_unmap && folio_mapped(folio))
 			goto move;
 
 		/*
-		 * Be careful not to clear PageLRU until after we're
-		 * sure the page is not being freed elsewhere -- the
-		 * page release code relies on it.
+		 * Be careful not to clear the lru flag until after we're
+		 * sure the folio is not being freed elsewhere -- the
+		 * folio release code relies on it.
 		 */
-		if (unlikely(!get_page_unless_zero(page)))
+		if (unlikely(!folio_try_get(folio)))
 			goto move;
 
-		if (!TestClearPageLRU(page)) {
-			/* Another thread is already isolating this page */
-			put_page(page);
+		if (!folio_test_clear_lru(folio)) {
+			/* Another thread is already isolating this folio */
+			folio_put(folio);
 			goto move;
 		}
 
 		nr_taken += nr_pages;
-		nr_zone_taken[page_zonenum(page)] += nr_pages;
+		nr_zone_taken[folio_zonenum(folio)] += nr_pages;
 		move_to = dst;
 move:
-		list_move(&page->lru, move_to);
+		list_move(&folio->lru, move_to);
 	}
 
 	/*
-	 * Splice any skipped pages to the start of the LRU list. Note that
+	 * Splice any skipped folios to the start of the LRU list. Note that
 	 * this disrupts the LRU order when reclaiming for lower zones but
 	 * we cannot splice to the tail. If we did then the SWAP_CLUSTER_MAX
-	 * scanning would soon rescan the same pages to skip and waste lots
+	 * scanning would soon rescan the same folios to skip and waste lots
 	 * of cpu cycles.
 	 */
-	if (!list_empty(&pages_skipped)) {
+	if (!list_empty(&folios_skipped)) {
 		int zid;
 
-		list_splice(&pages_skipped, src);
+		list_splice(&folios_skipped, src);
 		for (zid = 0; zid < MAX_NR_ZONES; zid++) {
 			if (!nr_skipped[zid])
 				continue;