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From: Peter Collingbourne <pcc@google.com>
To: catalin.marinas@arm.com, andreyknvl@gmail.com
Cc: Peter Collingbourne <pcc@google.com>,
	linux-mm@kvack.org, kasan-dev@googlegroups.com,
	 ryabinin.a.a@gmail.com, linux-arm-kernel@lists.infradead.org,
	 vincenzo.frascino@arm.com, will@kernel.org, eugenis@google.com
Subject: [PATCH] kasan: call clear_page with a match-all tag instead of changing page tag
Date: Wed, 15 Feb 2023 22:47:26 -0800	[thread overview]
Message-ID: <20230216064726.2724268-1-pcc@google.com> (raw)

Instead of changing the page's tag solely in order to obtain a pointer
with a match-all tag and then changing it back again, just convert the
pointer that we get from kmap_atomic() into one with a match-all tag
before passing it to clear_page().

On a certain microarchitecture, this has been observed to cause a
measurable improvement in microbenchmark performance, presumably as a
result of being able to avoid the atomic operations on the page tag.

Signed-off-by: Peter Collingbourne <pcc@google.com>
Link: https://linux-review.googlesource.com/id/I0249822cc29097ca7a04ad48e8eb14871f80e711
---
 include/linux/highmem.h | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/include/linux/highmem.h b/include/linux/highmem.h
index 44242268f53b..bbfa546dd602 100644
--- a/include/linux/highmem.h
+++ b/include/linux/highmem.h
@@ -245,12 +245,10 @@ static inline void clear_highpage(struct page *page)
 
 static inline void clear_highpage_kasan_tagged(struct page *page)
 {
-	u8 tag;
+	void *kaddr = kmap_atomic(page);
 
-	tag = page_kasan_tag(page);
-	page_kasan_tag_reset(page);
-	clear_highpage(page);
-	page_kasan_tag_set(page, tag);
+	clear_page(kasan_reset_tag(kaddr));
+	kunmap_atomic(kaddr);
 }
 
 #ifndef __HAVE_ARCH_TAG_CLEAR_HIGHPAGE
-- 
2.39.1.581.gbfd45094c4-goog


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WARNING: multiple messages have this Message-ID (diff)
From: Peter Collingbourne <pcc@google.com>
To: catalin.marinas@arm.com, andreyknvl@gmail.com
Cc: Peter Collingbourne <pcc@google.com>,
	linux-mm@kvack.org, kasan-dev@googlegroups.com,
	 ryabinin.a.a@gmail.com, linux-arm-kernel@lists.infradead.org,
	 vincenzo.frascino@arm.com, will@kernel.org, eugenis@google.com
Subject: [PATCH] kasan: call clear_page with a match-all tag instead of changing page tag
Date: Wed, 15 Feb 2023 22:47:26 -0800	[thread overview]
Message-ID: <20230216064726.2724268-1-pcc@google.com> (raw)

Instead of changing the page's tag solely in order to obtain a pointer
with a match-all tag and then changing it back again, just convert the
pointer that we get from kmap_atomic() into one with a match-all tag
before passing it to clear_page().

On a certain microarchitecture, this has been observed to cause a
measurable improvement in microbenchmark performance, presumably as a
result of being able to avoid the atomic operations on the page tag.

Signed-off-by: Peter Collingbourne <pcc@google.com>
Link: https://linux-review.googlesource.com/id/I0249822cc29097ca7a04ad48e8eb14871f80e711
---
 include/linux/highmem.h | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/include/linux/highmem.h b/include/linux/highmem.h
index 44242268f53b..bbfa546dd602 100644
--- a/include/linux/highmem.h
+++ b/include/linux/highmem.h
@@ -245,12 +245,10 @@ static inline void clear_highpage(struct page *page)
 
 static inline void clear_highpage_kasan_tagged(struct page *page)
 {
-	u8 tag;
+	void *kaddr = kmap_atomic(page);
 
-	tag = page_kasan_tag(page);
-	page_kasan_tag_reset(page);
-	clear_highpage(page);
-	page_kasan_tag_set(page, tag);
+	clear_page(kasan_reset_tag(kaddr));
+	kunmap_atomic(kaddr);
 }
 
 #ifndef __HAVE_ARCH_TAG_CLEAR_HIGHPAGE
-- 
2.39.1.581.gbfd45094c4-goog



             reply	other threads:[~2023-02-16  6:48 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-02-16  6:47 Peter Collingbourne [this message]
2023-02-16  6:47 ` [PATCH] kasan: call clear_page with a match-all tag instead of changing page tag Peter Collingbourne
2023-02-16 14:27 ` Catalin Marinas
2023-02-16 14:27   ` Catalin Marinas
2023-02-16 20:04   ` Peter Collingbourne
2023-02-16 20:04     ` Peter Collingbourne

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