From:   andrey.konovalov@linux.dev
To:     Andrew Morton <akpm@linux-foundation.org>
Cc:     Andrey Konovalov <andreyknvl@gmail.com>,
        Marco Elver <elver@google.com>,
        Alexander Potapenko <glider@google.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Andrey Ryabinin <ryabinin.a.a@gmail.com>,
        kasan-dev@googlegroups.com, linux-mm@kvack.org,
        Vincenzo Frascino <vincenzo.frascino@arm.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        linux-arm-kernel@lists.infradead.org,
        Peter Collingbourne <pcc@google.com>,
        Evgenii Stepanov <eugenis@google.com>,
        linux-kernel@vger.kernel.org,
        Andrey Konovalov <andreyknvl@google.com>
Subject: [PATCH mm v5 07/39] mm: clarify __GFP_ZEROTAGS comment
Date:   Thu, 30 Dec 2021 20:12:09 +0100
Message-Id: <4ef9f470c0d41437d7a2a111e2c739957f49ee39.1640891329.git.andreyknvl@google.com>
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From: Andrey Konovalov <andreyknvl@google.com>

__GFP_ZEROTAGS is intended as an optimization: if memory is zeroed during
allocation, it's possible to set memory tags at the same time with little
performance impact.

Clarify this intention of __GFP_ZEROTAGS in the comment.

Signed-off-by: Andrey Konovalov <andreyknvl@google.com>

---

Changes v4->v5:
- Mention optimization intention in the comment.
---
 include/linux/gfp.h | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/include/linux/gfp.h b/include/linux/gfp.h
index 5f893d994dcd..19e55f3fdd04 100644
--- a/include/linux/gfp.h
+++ b/include/linux/gfp.h
@@ -228,8 +228,10 @@ struct vm_area_struct;
  *
  * %__GFP_ZERO returns a zeroed page on success.
  *
- * %__GFP_ZEROTAGS returns a page with zeroed memory tags on success, if
- * __GFP_ZERO is set.
+ * %__GFP_ZEROTAGS zeroes memory tags at allocation time if the memory itself
+ * is being zeroed (either via __GFP_ZERO or via init_on_alloc). This flag is
+ * intended for optimization: setting memory tags at the same time as zeroing
+ * memory has minimal additional performace impact.
  *
  * %__GFP_SKIP_KASAN_POISON returns a page which does not need to be poisoned
  * on deallocation. Typically used for userspace pages. Currently only has an
-- 
2.25.1