linux-kernel - [PATCH v3 2/3] mm/gup: small refactoring: simplify try_grab

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Date:   Thu, 12 Aug 2021 21:41:32 -0700
From:   John Hubbard <jhubbard@...dia.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
CC:     Matthew Wilcox <willy@...radead.org>,
        Christoph Hellwig <hch@....de>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        LKML <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
        <linux-s390@...r.kernel.org>, <linux-fsdevel@...r.kernel.org>,
        John Hubbard <jhubbard@...dia.com>
Subject: [PATCH v3 2/3] mm/gup: small refactoring: simplify try_grab_page()

try_grab_page() does the same thing as try_grab_compound_head(...,
refs=1, ...), just with a different API. So there is a lot of code
duplication there.

Change try_grab_page() to call try_grab_compound_head(), while keeping
the API contract identical for callers.

Also, now that try_grab_compound_head() always has a caller, remove the
__maybe_unused annotation.

Cc: Matthew Wilcox <willy@...radead.org>
Reviewed-by: Christoph Hellwig <hch@....de>
Signed-off-by: John Hubbard <jhubbard@...dia.com>
---
 include/linux/mm.h |  4 ++--
 mm/gup.c           | 35 +++++------------------------------
 2 files changed, 7 insertions(+), 32 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index ce8fc0fd6d6e..ba985eaf3f19 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1204,8 +1204,8 @@ static inline void get_page(struct page *page)
 }
 
 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_grab_compound_head(struct page *page, int refs,
+				    unsigned int flags);
 
 
 static inline __must_check bool try_get_page(struct page *page)
diff --git a/mm/gup.c b/mm/gup.c
index 52f08e3177e9..886d6148d3d0 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -124,8 +124,8 @@ static inline struct page *try_get_compound_head(struct page *page, int refs)
  * considered failure, and furthermore, a likely bug in the caller, so a warning
  * is also emitted.
  */
-__maybe_unused struct page *try_grab_compound_head(struct page *page,
-						   int refs, unsigned int flags)
+struct page *try_grab_compound_head(struct page *page,
+				    int refs, unsigned int flags)
 {
 	if (flags & FOLL_GET)
 		return try_get_compound_head(page, refs);
@@ -208,35 +208,10 @@ static void put_compound_head(struct page *page, int refs, unsigned int flags)
  */
 bool __must_check try_grab_page(struct page *page, unsigned int flags)
 {
-	WARN_ON_ONCE((flags & (FOLL_GET | FOLL_PIN)) == (FOLL_GET | FOLL_PIN));
+	if (!(flags & (FOLL_GET | FOLL_PIN)))
+		return true;
 
-	if (flags & FOLL_GET)
-		return try_get_page(page);
-	else if (flags & FOLL_PIN) {
-		int refs = 1;
-
-		page = compound_head(page);
-
-		if (WARN_ON_ONCE(page_ref_count(page) <= 0))
-			return false;
-
-		if (hpage_pincount_available(page))
-			hpage_pincount_add(page, 1);
-		else
-			refs = GUP_PIN_COUNTING_BIAS;
-
-		/*
-		 * Similar to try_grab_compound_head(): even if using the
-		 * hpage_pincount_add/_sub() routines, be sure to
-		 * *also* increment the normal page refcount field at least
-		 * once, so that the page really is pinned.
-		 */
-		page_ref_add(page, refs);
-
-		mod_node_page_state(page_pgdat(page), NR_FOLL_PIN_ACQUIRED, 1);
-	}
-
-	return true;
+	return try_grab_compound_head(page, 1, flags);
 }
 
 /**
-- 
2.32.0