Re: [PATCH v2] mm: Optimise put_pages_list()

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On 10/7/21 12:21 PM, Matthew Wilcox (Oracle) wrote:
Instead of calling put_page() one page at a time, pop pages off
the list if their refcount was too high and pass the remainder to
put_unref_page_list().  This should be a speed improvement, but I have
no measurements to support that.  Current callers do not care about
performance, but I hope to add some which do.

Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
---
v2:
  - Handle compound pages (Mel)
  - Comment why we don't need to handle PageLRU
  - Added call to __ClearPageWaiters(), matching that in release_pages()

  mm/swap.c | 23 ++++++++++++++++-------
  1 file changed, 16 insertions(+), 7 deletions(-)

diff --git a/mm/swap.c b/mm/swap.c
index af3cad4e5378..9f334d503fd2 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -134,18 +134,27 @@ EXPORT_SYMBOL(__put_page);
   * put_pages_list() - release a list of pages
   * @pages: list of pages threaded on page->lru
   *
- * Release a list of pages which are strung together on page.lru.  Currently
- * used by read_cache_pages() and related error recovery code.
+ * Release a list of pages which are strung together on page.lru.
   */
  void put_pages_list(struct list_head *pages)
  {
-	while (!list_empty(pages)) {
-		struct page *victim;
+	struct page *page, *next;
- victim = lru_to_page(pages);
-		list_del(&victim->lru);
-		put_page(victim);
+	list_for_each_entry_safe(page, next, pages, lru) {
+		if (!put_page_testzero(page)) {
+			list_del(&page->lru);
+			continue;
+		}


I know that compound pages are not currently passed to put_pages_list(),

but I assume the put_page_testzero() should only be done on the head

page similar to release_pages()?


Anthony

+		if (PageHead(page)) {
+			list_del(&page->lru);
+			__put_compound_page(page);
+			continue;
+		}
+		/* Cannot be PageLRU because it's passed to us using the lru */
+		__ClearPageWaiters(page);
  	}
+
+	free_unref_page_list(pages);
  }
  EXPORT_SYMBOL(put_pages_list);




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