linux-kernel - [PATCH 3/3] mm/gup: refactor and simplify try_get

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Date:   Sun, 8 Aug 2021 16:50:18 -0700
From:   John Hubbard <jhubbard@...dia.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Matthew Wilcox <willy@...radead.org>
CC:     LKML <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
        John Hubbard <jhubbard@...dia.com>
Subject: [PATCH 3/3] mm/gup: refactor and simplify try_get_page()

try_get_page() is very similar to try_get_compound_head(), and in fact
try_get_page() has fallen a little behind in terms of maintenance:
try_get_compound_head() handles speculative page references more
thoroughly.

Change try_get_page() so that it is implemented in terms of
try_get_compound_head(), but without changing try_get_page()'s API
contract.

Signed-off-by: John Hubbard <jhubbard@...dia.com>
---
 include/linux/mm.h | 11 ++++++-----
 mm/gup.c           |  2 +-
 2 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index ce8fc0fd6d6e..92d3b37357d5 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1207,14 +1207,15 @@ bool __must_check try_grab_page(struct page *page, unsigned int flags);
 __maybe_unused struct page *try_grab_compound_head(struct page *page, int refs,
 						   unsigned int flags);
 
+struct page *try_get_compound_head(struct page *page, int refs);
 
+/*
+ * This has the same functionality as try_get_compound_head(), just with a
+ * slightly different API.
+ */
 static inline __must_check bool try_get_page(struct page *page)
 {
-	page = compound_head(page);
-	if (WARN_ON_ONCE(page_ref_count(page) <= 0))
-		return false;
-	page_ref_inc(page);
-	return true;
+	return try_get_compound_head(page, 1) != NULL;
 }
 
 /**
diff --git a/mm/gup.c b/mm/gup.c
index 4be6f060fa0b..ba75906ba7f7 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -66,7 +66,7 @@ static void put_page_refs(struct page *page, int refs)
  * Return the compound head page with ref appropriately incremented,
  * or NULL if that failed.
  */
-static inline struct page *try_get_compound_head(struct page *page, int refs)
+struct page *try_get_compound_head(struct page *page, int refs)
 {
 	struct page *head = compound_head(page);
 
-- 
2.32.0