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Tue, 12 May 2026 21:52:29 +0800 (CST) Received: from dggpemf100008.china.huawei.com (unknown [7.185.36.138]) by mail.maildlp.com (Postfix) with ESMTPS id 2D04D40561; Tue, 12 May 2026 21:59:29 +0800 (CST) Received: from [10.174.177.243] (10.174.177.243) by dggpemf100008.china.huawei.com (7.185.36.138) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1544.11; Tue, 12 May 2026 21:59:28 +0800 Message-ID: <618380f2-ea7b-4855-9dc5-d655dc30d5a7@huawei.com> Date: Tue, 12 May 2026 21:59:26 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/damon/vaddr: attempt per-vma lock during page table walk To: SeongJae Park CC: Andrew Morton , , , References: <20260512013116.80435-1-sj@kernel.org> Content-Language: en-US From: Kefeng Wang In-Reply-To: <20260512013116.80435-1-sj@kernel.org> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-Originating-IP: [10.174.177.243] X-ClientProxiedBy: kwepems100001.china.huawei.com (7.221.188.238) To dggpemf100008.china.huawei.com (7.185.36.138) X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 04846140006 X-Stat-Signature: ho3indcobxyo9jgsbno8ke63jojutyoe X-Rspam-User: X-HE-Tag: 1778594376-100476 X-HE-Meta: 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 wUqJYSbF do/US0UUQQo+LA8KmwyTKadbX2Cl5gblH+/t5KYL4yAUcbrJHRhlQlV32nRbtze7ZOkb6mMKpYNK0Bo3pGSQ4Gw0M21uMf5BnqRIf2mHyR3054/1JpYUpTumT1l4POtlI1AHJ6HiE2vwgRIb3DXZQl6ETnKlbgQT7BPAJbzRCSuyfxJdMKCtW1UHR4QB8VHT81pgLkuMHN2Ed8MYudnn3dbMMly9P9yCTR0fBjmuLWdvE2/wTqoGgWWczUSbuMrTpSZYJM9esq9Mm8e6ODpZSb2tScvLsiFWWx5wA/HacrM2SOfLA5gQXMZ5JMlyK6eBkLktDYKDi14zpAYS3HYjmS9SwCcDpsiMWbhg0Pd6LzNvLgryRH3aV3/oy9J2+Q5rvJXKZxZFAmD8mpaiXcNV7DAamhajX3ABrbrzKCn88IPR3RcU= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 5/12/2026 9:31 AM, SeongJae Park wrote: > On Mon, 11 May 2026 21:25:46 +0800 Kefeng Wang wrote: > >> Currently, DAMON virtual address operations use mmap_read_lock >> during page table walks, which can cause unnecessary contention >> under high concurrency. >> >> Introduce damon_va_walk_page_range() to first attempt acquiring a >> per-vma lock. If the VMA is found and the range is fully contained >> within it, the page table walk proceeds with the per-vma lock >> instead of mmap_read_lock. >> >> This optimization is particularly effective for damon_va_young() >> and damon_va_mkold(), which are frequently called and typically >> operate within a single VMA. > > Makes sense. Do you have some measurements? In fact, I do not have performance-related tests. > >> >> Signed-off-by: Kefeng Wang > > Looks good to me. Nonetheless, because I'm not familiar with per-vma locking, > I'd like to wait for Sashiko review. > Sashiko review reports a issue about handling VMAs with the VM_PFNMAP flag inconsistently[1]，We indeed do not need to handle the vma of VM_PFNMAP for damon, so a quick fix is as follows, diff --git a/mm/damon/vaddr.c b/mm/damon/vaddr.c index eed2ae132a58..d27147603564 100644 --- a/mm/damon/vaddr.c +++ b/mm/damon/vaddr.c @@ -251,8 +251,11 @@ static void damon_va_walk_page_range(struct mm_struct *mm, unsigned long start, goto lock_mmap; } - ops->walk_lock = PGWALK_VMA_RDLOCK_VERIFY; - walk_page_range_vma(vma, start, end, ops, private); + if (!(vma->vm_flags & VM_PFNMAP)) { + ops->walk_lock = PGWALK_VMA_RDLOCK_VERIFY; + walk_page_range_vma(vma, start, end, ops, private); + } + vma_end_read(vma); return; Any more comments? Thanks. [1] https://sashiko.dev/#/patchset/20260511132546.1973270-1-wangkefeng.wang@huawei.com?part=1 > > Thanks, > SJ > > [...] >