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Wed, 30 Jul 2025 10:23:25 +0800 From: Zhang Qilong To: , CC: , , , , , Subject: [PATCH v2] /dev/zero: try to align PMD_SIZE for private mapping Date: Wed, 30 Jul 2025 10:22:06 +0800 Message-ID: <20250730022206.1349706-1-zhangqilong3@huawei.com> X-Mailer: git-send-email 2.43.0 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain X-Originating-IP: [10.175.124.71] X-ClientProxiedBy: kwepems100002.china.huawei.com (7.221.188.206) To dggpemf500012.china.huawei.com (7.185.36.8) X-Rspamd-Queue-Id: 66F96140007 X-Stat-Signature: u3gqe8uhgqp98txhneuns1amr4ub351f X-Rspam-User: X-Rspamd-Server: rspam07 X-HE-Tag: 1753842210-77296 X-HE-Meta: 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 dl2xy9nv k8qNP/Iku7E6FknXKav0bsnrJjWFVDiNo9PMz25o03PrNx6ERQlZPcjrmt9bC/dq8lp51D+HO1ScVsmMwN7Hjk1WewHKggUF1sdIKCtSU4vOGrCmnCdRHS2l4GiawWAXdsMSa2nnWXBEuyj49zqJjC3pBZTS0NbvzciW58TXqCb7ueoFmCa8OtX5Zujw8eXqd7mjGUxaG5XylQckD7tAmaHzi+xvYja8LuZURHbh/XpgqDbY= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: If THP is enable, mapping /dev/zero with a size larger than 2MB could achieve performance gains by allocating aligned address. The mprot_tw4m in libMicro average execution time on arm64: - Test case: mprot_tw4m - Before the patch: 22 us - After the patch: 17 us Signed-off-by: Zhang Qilong --- drivers/char/mem.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/drivers/char/mem.c b/drivers/char/mem.c index 48839958b0b1..3699e716b84e 100644 --- a/drivers/char/mem.c +++ b/drivers/char/mem.c @@ -525,12 +525,20 @@ static unsigned long get_unmapped_area_zero(struct file *file, * so as not to confuse shmem with our handle on "/dev/zero". */ return shmem_get_unmapped_area(NULL, addr, len, pgoff, flags); } +#ifdef CONFIG_TRANSPARENT_HUGEPAGE + /* + * Attempt to map aligned to huge page size if possible, otherwise we + * fall back to system page size mappings in thp_get_unmapped_area. + */ + return thp_get_unmapped_area(file, addr, len, pgoff, flags); +#else /* Otherwise flags & MAP_PRIVATE: with no shmem object beneath it */ return mm_get_unmapped_area(current->mm, file, addr, len, pgoff, flags); +#endif #else return -ENOSYS; #endif } -- 2.43.0