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Tue, 29 Jul 2025 21:51:10 +0800 From: Zhang Qilong To: , CC: , , , , Subject: [PATCH] /dev/zero: try to align PMD_SIZE for private mapping Date: Tue, 29 Jul 2025 21:49:41 +0800 Message-ID: <20250729134942.900517-1-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: kwepems200001.china.huawei.com (7.221.188.67) To dggpemf500012.china.huawei.com (7.185.36.8) X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 600C7180006 X-Stat-Signature: qu9igsaqrywr96dyi4yyyqxbj7na9s6t X-Rspam-User: X-HE-Tag: 1753797075-514797 X-HE-Meta: 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 p1DUT0zx lv25VUzRb1unKznvzTW8PTABFsSk+QrObrkZ7mnw6SnqpW0hUDZLTFrO81qUk3PPgOhRsDq/DntuOAqlQdI4isHp8YZQdCgghxXE3/xjwrF5DZyny0mtU2I7pyF6ZcM0WrwWzgM8wHngxDPqNay84yDyy2hPK5ggq/JHMMW1m5mbhdv8WZQVRtrJ9rTMxKvu4iIrNJ91zA423LDLJ0FAk8FQRGjMECGCUT+ak2Y0iJD6h1ObcewIoNMXeMJBOfiOAXGHV/8adF52mOYE= 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: By default, THP are usually enabled. 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 | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/drivers/char/mem.c b/drivers/char/mem.c index 48839958b0b1..c57327ca9dd6 100644 --- a/drivers/char/mem.c +++ b/drivers/char/mem.c @@ -515,10 +515,12 @@ static int mmap_zero(struct file *file, struct vm_area_struct *vma) static unsigned long get_unmapped_area_zero(struct file *file, unsigned long addr, unsigned long len, unsigned long pgoff, unsigned long flags) { #ifdef CONFIG_MMU + unsigned long ret; + if (flags & MAP_SHARED) { /* * mmap_zero() will call shmem_zero_setup() to create a file, * so use shmem's get_unmapped_area in case it can be huge; * and pass NULL for file as in mmap.c's get_unmapped_area(), @@ -526,10 +528,13 @@ static unsigned long get_unmapped_area_zero(struct file *file, */ return shmem_get_unmapped_area(NULL, addr, len, pgoff, flags); } /* Otherwise flags & MAP_PRIVATE: with no shmem object beneath it */ + ret = thp_get_unmapped_area(file, addr, len, pgoff, flags); + if (ret) + return ret; return mm_get_unmapped_area(current->mm, file, addr, len, pgoff, flags); #else return -ENOSYS; #endif } -- 2.43.0