Re: [RFC PATCH] mm/memory-failure: release private data before split THP

[Matthew Wilcox <willy@infradead.org>]

On Wed, Aug 03, 2022 at 10:52:43AM +0800, Yin Fengwei wrote:
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index da39ec8afca8..08e21973b120 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -1484,7 +1484,16 @@ static int identify_page_state(unsigned long pfn, struct page *p,
>  
>  static int try_to_split_thp_page(struct page *page, const char *msg)
>  {
> +	struct page *head = compound_head(page);
 > +
>  	lock_page(page);
> +	/*
> +	 * If thp page has private data attached, thp split will fail.
> +	 * Release private data before split thp.
> +	 */
> +	if (page_has_private(head))
> +		try_to_release_page(head, GFP_KERNEL);
> +
>  	if (unlikely(split_huge_page(page))) {
>  		unsigned long pfn = page_to_pfn(page);

It seems a shame to use the old page approach instead of the
shiny new folio approach.  We're quite close to being able to remove
try_to_release_page() in 6.1 or 6.2 so adding a new caller is a bad idea.
How about this:

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index da39ec8afca8..765b383288b1 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -1484,16 +1484,21 @@ static int identify_page_state(unsigned long pfn, struct page *p,
 
 static int try_to_split_thp_page(struct page *page, const char *msg)
 {
-	lock_page(page);
+	struct folio *folio = page_folio(page);
+
+	folio_lock(folio);
+	if (folio_test_private(folio))
+		filemap_release_folio(folio, GFP_KERNEL);
 	if (unlikely(split_huge_page(page))) {
 		unsigned long pfn = page_to_pfn(page);
 
-		unlock_page(page);
+		folio_unlock(folio);
 		pr_info("%s: %#lx: thp split failed\n", msg, pfn);
-		put_page(page);
+		folio_put(folio);
 		return -EBUSY;
 	}
-	unlock_page(page);
+	folio = page_folio(page);
+	folio_unlock(folio);
 
 	return 0;
 }