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From:   john.hubbard@gmail.com
To:     Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org
Cc:     Al Viro <viro@zeniv.linux.org.uk>,
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        Ralph Campbell <rcampbell@nvidia.com>,
        Tom Talpey <tom@talpey.com>,
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        Nick Piggin <npiggin@suse.de>,
        Dave Kleikamp <shaggy@linux.vnet.ibm.com>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>
Subject: [PATCH 3/6] mm: page_cache_add_speculative(): refactoring
Date:   Sun,  3 Feb 2019 21:21:32 -0800
Message-Id: <20190204052135.25784-4-jhubbard@nvidia.com>
In-Reply-To: <20190204052135.25784-1-jhubbard@nvidia.com>
References: <20190204052135.25784-1-jhubbard@nvidia.com>
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From: John Hubbard <jhubbard@nvidia.com>

This combines the common elements of these routines:

    page_cache_get_speculative()
    page_cache_add_speculative()

This was anticipated by the original author, as shown by the comment
in commit ce0ad7f095258 ("powerpc/mm: Lockless get_user_pages_fast()
for 64-bit (v3)"):

    "Same as above, but add instead of inc (could just be merged)"

An upcoming patch for get_user_pages() tracking will use these routines,
so let's remove the duplication now.

There is no intention to introduce any behavioral change, but there is a
small risk of that, due to slightly differing ways of expressing the
TINY_RCU and related configurations.

Cc: Nick Piggin <npiggin@suse.de>
Cc: Dave Kleikamp <shaggy@linux.vnet.ibm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
 include/linux/pagemap.h | 33 +++++++++++----------------------
 1 file changed, 11 insertions(+), 22 deletions(-)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index e2d7039af6a3..5c8a9b59cbdc 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -164,8 +164,10 @@ void release_pages(struct page **pages, int nr);
  * will find the page or it will not. Likewise, the old find_get_page could run
  * either before the insertion or afterwards, depending on timing.
  */
-static inline int page_cache_get_speculative(struct page *page)
+static inline int __page_cache_add_speculative(struct page *page, int count)
 {
+	VM_BUG_ON(in_interrupt());
+
 #ifdef CONFIG_TINY_RCU
 # ifdef CONFIG_PREEMPT_COUNT
 	VM_BUG_ON(!in_atomic() && !irqs_disabled());
@@ -180,10 +182,10 @@ static inline int page_cache_get_speculative(struct page *page)
 	 * SMP requires.
 	 */
 	VM_BUG_ON_PAGE(page_count(page) == 0, page);
-	page_ref_inc(page);
+	page_ref_add(page, count);
 
 #else
-	if (unlikely(!get_page_unless_zero(page))) {
+	if (unlikely(!page_ref_add_unless(page, count, 0))) {
 		/*
 		 * Either the page has been freed, or will be freed.
 		 * In either case, retry here and the caller should
@@ -197,27 +199,14 @@ static inline int page_cache_get_speculative(struct page *page)
 	return 1;
 }
 
-/*
- * Same as above, but add instead of inc (could just be merged)
- */
-static inline int page_cache_add_speculative(struct page *page, int count)
+static inline int page_cache_get_speculative(struct page *page)
 {
-	VM_BUG_ON(in_interrupt());
-
-#if !defined(CONFIG_SMP) && defined(CONFIG_TREE_RCU)
-# ifdef CONFIG_PREEMPT_COUNT
-	VM_BUG_ON(!in_atomic() && !irqs_disabled());
-# endif
-	VM_BUG_ON_PAGE(page_count(page) == 0, page);
-	page_ref_add(page, count);
-
-#else
-	if (unlikely(!page_ref_add_unless(page, count, 0)))
-		return 0;
-#endif
-	VM_BUG_ON_PAGE(PageCompound(page) && page != compound_head(page), page);
+	return __page_cache_add_speculative(page, 1);
+}
 
-	return 1;
+static inline int page_cache_add_speculative(struct page *page, int count)
+{
+	return __page_cache_add_speculative(page, count);
 }
 
 #ifdef CONFIG_NUMA
-- 
2.20.1