[PATCHv2] mm: No need to check pcp page when free it to buddy

[PATCHv2] mm: No need to check pcp page when free it to buddy

[zhaoyang.huang]

From: Zhaoyang Huang <zhaoyang.huang@unisoc.com>

The pages on pcp list have been checked the validity via bellowing call chain.
It is no need to check it again when free them back to buddy by free_pcppages_bulk.

free_unref_page\free_unref_page_list
{
...
	//page's validity is checked here
	if (!free_unref_page_prepare(page, pfn, order))
		return;
...
	//page added to pcp->lists and status is ready for moving to buddy
	list_add(&page->lru, &pcp->lists[pindex]);

Signed-off-by: Zhaoyang Huang <zhaoyang.huang@unisoc.com>
---
v2: update code and comment for clarifying
---
---
 mm/page_alloc.c | 16 ----------------
 1 file changed, 16 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index e008a3d..1472ebc 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1420,14 +1420,6 @@ static bool free_pcp_prepare(struct page *page, unsigned int order)
 {
 	return free_pages_prepare(page, order, true, FPI_NONE);
 }
-
-static bool bulkfree_pcp_prepare(struct page *page)
-{
-	if (debug_pagealloc_enabled_static())
-		return check_free_page(page);
-	else
-		return false;
-}
 #else
 /*
  * With DEBUG_VM disabled, order-0 pages being freed are checked only when
@@ -1442,11 +1434,6 @@ static bool free_pcp_prepare(struct page *page, unsigned int order)
 	else
 		return free_pages_prepare(page, order, false, FPI_NONE);
 }
-
-static bool bulkfree_pcp_prepare(struct page *page)
-{
-	return check_free_page(page);
-}
 #endif /* CONFIG_DEBUG_VM */
 
 /*
@@ -1512,9 +1499,6 @@ static void free_pcppages_bulk(struct zone *zone, int count,
 			count -= nr_pages;
 			pcp->count -= nr_pages;
 
-			if (bulkfree_pcp_prepare(page))
-				continue;
-
 			/* MIGRATE_ISOLATE page should not go to pcplists */
 			VM_BUG_ON_PAGE(is_migrate_isolate(mt), page);
 			/* Pageblock could have been isolated meanwhile */
-- 
1.9.1

Re: [PATCHv2] mm: No need to check pcp page when free it to buddy

[Andrew Morton]

On Thu, 15 Sep 2022 10:40:54 +0800 "zhaoyang.huang" <zhaoyang.huang@unisoc.com> wrote:

> From: Zhaoyang Huang <zhaoyang.huang@unisoc.com>
> 
> The pages on pcp list have been checked the validity via bellowing call chain.
> It is no need to check it again when free them back to buddy by free_pcppages_bulk.
> 
> free_unref_page\free_unref_page_list
> {
> ...
> 	//page's validity is checked here
> 	if (!free_unref_page_prepare(page, pfn, order))
> 		return;
> ...
> 	//page added to pcp->lists and status is ready for moving to buddy
> 	list_add(&page->lru, &pcp->lists[pindex]);
> 

The comment over free_pcp_prepare():

/*
 * With DEBUG_VM enabled, order-0 pages are checked immediately when being freed
 * to pcp lists. With debug_pagealloc also enabled, they are also rechecked when
 * moved from pcp lists to free lists.
 */

Which seems sensible - a page's state may have been messed up while
it's in the pcp lists.