linux-kernel - Re: [PATCH mm-unstable] mm: move folio_set_compound

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Date:   Fri, 16 Dec 2022 14:27:33 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Sidhartha Kumar <sidhartha.kumar@...cle.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        songmuchun@...edance.com, mike.kravetz@...cle.com,
        willy@...radead.org, jhubbard@...dia.com
Subject: Re: [PATCH mm-unstable] mm: move folio_set_compound_order() to
 mm/internal.h

On Tue, 13 Dec 2022 13:20:53 -0800 Sidhartha Kumar <sidhartha.kumar@...cle.com> wrote:

> folio_set_compound_order() is moved to an mm-internal location so external
> folio users cannot misuse this function. Change the name of the function
> to folio_set_order() and use WARN_ON_ONCE() rather than BUG_ON. Also,
> handle the case if a non-large folio is passed and add clarifying comments
> to the function.
> 

This differs from the version I previously merged:

--- a/mm/internal.h~mm-move-folio_set_compound_order-to-mm-internalh-update
+++ a/mm/internal.h
@@ -384,8 +384,10 @@ int split_free_page(struct page *free_pa
  */
 static inline void folio_set_order(struct folio *folio, unsigned int order)
 {
-	if (WARN_ON_ONCE(!folio_test_large(folio)))
+	if (!folio_test_large(folio)) {
+		WARN_ON_ONCE(order);
 		return;
+	}
 
 	folio->_folio_order = order;
 #ifdef CONFIG_64BIT

Makes sense.  But wouldn't

	if (WARN_ON_ONCE(order && !folio_test_large(folio)))

be clearer?