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Thu, 31 Jul 2025 16:38:15 +0800 From: Zhang Qilong To: , , CC: , , , , , Zhang Qilong , David Hildenbrand Subject: [PATCH v3] /dev/zero: try to align PMD_SIZE for private mapping Date: Thu, 31 Jul 2025 16:36:55 +0800 Message-ID: <20250731083655.1558076-1-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-Server: rspam03 X-Rspamd-Queue-Id: 14284A0006 X-Stat-Signature: wdrmdn19e4iua81w5xazkcatjszzngzc X-Rspam-User: X-HE-Tag: 1753951100-523053 X-HE-Meta: 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 LzXHjkAv KAQkPLwUy7gqp1ytI+0zyTjzo4ygrx/FqvW6MObd8K+INfZDNZFCh0Dw0T+nNGrKUKZc3VjQCihkaHvAMi1i3GGwjPz0J3mCJ28x3LGHJgR9vaP0yUu9VVtvyIPACPOFe8MpwFNtKG4Iin3QnMnWGaeqeo9Rg1oa2MUj2eCAb1AsijqnrifdoSl49NT0z/GJNNjH0MFV6VXuPDRH8IZ28bFPFf9tIWAnU7EJVO7DVMxRZtbgNRt326GtlsJp0g8vRkhX5 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: Attempt to map aligned to huge page size for private mapping which could achieve performance gains, the mprot_tw4m in libMicro average execution time on arm64: - Test case: mprot_tw4m - Before the patch: 22 us - After the patch: 17 us If THP config is not set, we fall back to system page size mappings. Acked-by: David Hildenbrand Signed-off-by: Zhang Qilong --- v3: - collect Acked-by - factor out the #ifdef CONFIG_MMU in get_unmapped_area_zero(), per Lorenzo - explicitly use #ifdef CONFIG_TRANSPARENT_HUGEPAGE, per Lorenzo and Matthew v2: - add comments on code suggested by Lorenzo - use IS_ENABLED to check THP config drivers/char/mem.c | 21 +++++++++++++++++---- 1 file changed, 17 insertions(+), 4 deletions(-) diff --git a/drivers/char/mem.c b/drivers/char/mem.c index 48839958b0b1..b7c4dbe4d2c1 100644 --- a/drivers/char/mem.c +++ b/drivers/char/mem.c @@ -510,31 +510,44 @@ static int mmap_zero(struct file *file, struct vm_area_struct *vma) return shmem_zero_setup(vma); vma_set_anonymous(vma); return 0; } +#ifndef CONFIG_MMU +static unsigned long get_unmapped_area_zero(struct file *file, + unsigned long addr, unsigned long len, + unsigned long pgoff, unsigned long flags) +{ + return -ENOSYS; +} +#else 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 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(), * so as not to confuse shmem with our handle on "/dev/zero". */ return shmem_get_unmapped_area(NULL, addr, len, pgoff, flags); } - /* Otherwise flags & MAP_PRIVATE: with no shmem object beneath it */ - return mm_get_unmapped_area(current->mm, file, addr, len, pgoff, flags); + /* + * Otherwise flags & MAP_PRIVATE: with no shmem object beneath it, + * attempt to map aligned to huge page size if possible, otherwise we + * fall back to system page size mappings. + */ +#ifdef CONFIG_TRANSPARENT_HUGEPAGE + return thp_get_unmapped_area(file, addr, len, pgoff, flags); #else - return -ENOSYS; + return mm_get_unmapped_area(current->mm, file, addr, len, pgoff, flags); #endif } +#endif static ssize_t write_full(struct file *file, const char __user *buf, size_t count, loff_t *ppos) { return -ENOSPC; -- 2.43.0