diff mbox series

[mm,v5,07/39] mm: clarify __GFP_ZEROTAGS comment

Message ID	4ef9f470c0d41437d7a2a111e2c739957f49ee39.1640891329.git.andreyknvl@google.com (mailing list archive)
State	New
Headers	show Return-Path: <owner-linux-mm@kvack.org> 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> In-Reply-To: <cover.1640891329.git.andreyknvl@google.com> References: <cover.1640891329.git.andreyknvl@google.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Sender: owner-linux-mm@kvack.org Precedence: bulk
Series	kasan, vmalloc, arm64: add vmalloc tagging support for SW/HW_TAGS \| expand [mm,v5,00/39] kasan, vmalloc, arm64: add vmalloc tagging support for SW/HW_TAGS [mm,v5,01/39] kasan, page_alloc: deduplicate should_skip_kasan_poison [mm,v5,02/39] kasan, page_alloc: move tag_clear_highpage out of kernel_init_free_pages [mm,v5,03/39] kasan, page_alloc: merge kasan_free_pages into free_pages_prepare [mm,v5,04/39] kasan, page_alloc: simplify kasan_poison_pages call site [mm,v5,05/39] kasan, page_alloc: init memory of skipped pages on free [mm,v5,06/39] kasan: drop skip_kasan_poison variable in free_pages_prepare [mm,v5,07/39] mm: clarify __GFP_ZEROTAGS comment [mm,v5,08/39] kasan: only apply __GFP_ZEROTAGS when memory is zeroed [mm,v5,09/39] kasan, page_alloc: refactor init checks in post_alloc_hook [mm,v5,10/39] kasan, page_alloc: merge kasan_alloc_pages into post_alloc_hook [mm,v5,11/39] kasan, page_alloc: combine tag_clear_highpage calls in post_alloc_hook [mm,v5,12/39] kasan, page_alloc: move SetPageSkipKASanPoison in post_alloc_hook [mm,v5,13/39] kasan, page_alloc: move kernel_init_free_pages in post_alloc_hook [mm,v5,14/39] kasan, page_alloc: rework kasan_unpoison_pages call site [mm,v5,15/39] kasan: clean up metadata byte definitions [mm,v5,16/39] kasan: define KASAN_VMALLOC_INVALID for SW_TAGS [mm,v5,17/39] kasan, x86, arm64, s390: rename functions for modules shadow [mm,v5,18/39] kasan, vmalloc: drop outdated VM_KASAN comment [mm,v5,19/39] kasan: reorder vmalloc hooks [mm,v5,20/39] kasan: add wrappers for vmalloc hooks [mm,v5,21/39] kasan, vmalloc: reset tags in vmalloc functions [mm,v5,22/39] kasan, fork: reset pointer tags of vmapped stacks [mm,v5,23/39] kasan, arm64: reset pointer tags of vmapped stacks [mm,v5,24/39] kasan, vmalloc: add vmalloc tagging for SW_TAGS [mm,v5,25/39] kasan, vmalloc, arm64: mark vmalloc mappings as pgprot_tagged [mm,v5,26/39] kasan, vmalloc: unpoison VM_ALLOC pages after mapping [mm,v5,27/39] kasan, mm: only define ___GFP_SKIP_KASAN_POISON with HW_TAGS [mm,v5,28/39] kasan, page_alloc: allow skipping unpoisoning for HW_TAGS [mm,v5,29/39] kasan, page_alloc: allow skipping memory init for HW_TAGS [mm,v5,30/39] kasan, vmalloc: add vmalloc tagging for HW_TAGS [mm,v5,31/39] kasan, vmalloc: only tag normal vmalloc allocations [mm,v5,32/39] kasan, arm64: don't tag executable vmalloc allocations [mm,v5,33/39] kasan: mark kasan_arg_stacktrace as __initdata [mm,v5,34/39] kasan: clean up feature flags for HW_TAGS mode [mm,v5,35/39] kasan: add kasan.vmalloc command line flag [mm,v5,36/39] kasan: allow enabling KASAN_VMALLOC and SW/HW_TAGS [mm,v5,37/39] arm64: select KASAN_VMALLOC for SW/HW_TAGS modes [mm,v5,38/39] kasan: documentation updates [mm,v5,39/39] kasan: improve vmalloc tests

Commit Message

andrey.konovalov@linux.dev Dec. 30, 2021, 7:12 p.m. UTC

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 mbox series

Patch

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