Re: [PATCH 6/8] mm/memory-failure: Convert memory_failure() to use a folio

[Matthew Wilcox <willy@infradead.org>]

On Fri, Mar 08, 2024 at 04:48:33PM +0800, Miaohe Lin wrote:
> On 2024/3/1 5:20, Matthew Wilcox (Oracle) wrote:
> > @@ -2277,8 +2277,8 @@ int memory_failure(unsigned long pfn, int flags)
> >  		}
> >  	}
> >  
> > -	hpage = compound_head(p);
> > -	if (PageTransHuge(hpage)) {
> > +	folio = page_folio(p);
> > +	if (folio_test_large(folio)) {
> >  		/*
> >  		 * The flag must be set after the refcount is bumped
> >  		 * otherwise it may race with THP split.
[...]
> > @@ -2318,11 +2319,11 @@ int memory_failure(unsigned long pfn, int flags)
> >  	 * race window. If this happens, we could try again to hopefully
> >  	 * handle the page next round.
> >  	 */
> > -	if (PageCompound(p)) {
> > +	if (folio_test_large(folio)) {
> 
> folio_test_large() only checks whether PG_head is set but PageCompound() also checks PageTail().
> So folio_test_large() and PageCompound() are not equivalent?

Assuming we have a refcount on this page so it can't be simultaneously
split/freed/whatever, these three sequences are equivalent:

1	if (PageCompound(p))

2	struct page *head = compound_head(p);
2	if (PageHead(head))

3	struct folio *folio = page_folio(p);
3	if (folio_test_large(folio))