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b=VkZe/WFSuj2qphIdEos+JKuocohvTsGiCAtNapnNm/aM0jFSc777+gDrDZV553DQ2 fIJjRYQVKFnKJ1Q5TEhtK6aysXdSRNU3OxXhGA9omEu+KbBRKX6fYeg7q3hgnEnGBq gR4Dcf+YG/86EYn6GCQ6lxpFKjbMfxCo5fmq7QH4vn3x1TiD/7OiIIRNChkQCuAlNq UEIhpfMVmUNy7yHfY8B8TO7bg8XA9hOh7gudXJCGxWgQT5DqpgL2GW/MPqB70+nRL5 miwmpdKHWHQJGVQ4ZMw0gTSdm9vX+iWdID4XuYTpDC6I0ybKFcvKZ+xY/xdiX3JioH 0ibk0HktNvOYQ== From: SeongJae Park To: Kefeng Wang Cc: SeongJae Park , Andrew Morton , damon@lists.linux.dev, linux-mm@kvack.org, sunnanyong@huawei.com Subject: Re: [PATCH] mm/damon/vaddr: attempt per-vma lock during page table walk Date: Tue, 12 May 2026 07:08:52 -0700 Message-ID: <20260512140854.111278-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <618380f2-ea7b-4855-9dc5-d655dc30d5a7@huawei.com> References: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Queue-Id: 670F6C000E X-Rspamd-Server: rspam04 X-Stat-Signature: tb9ygogsuqwmpd7h1d9igq5nnes6rerk X-HE-Tag: 1778594948-558973 X-HE-Meta: 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 vJ5lsW8X P650aeMiG9cmPJCFSsKq83u0vEBJW1dkWIJ9SAt/P0l/6Zf7NhIHtrJV+Zn0XpwrxIEqFDCJvu6ZC+6UPiWiLBgglWlWBweARkyRI5PXoLLcbCZnQuEtYYLooH90adgegQwj/qYX7WsI8mt4hA2XNzWfUm+D1J8s0/Ax6s0xf5Th9aP1QCsjQmVjmQFYUC3edTIPBM6DZtdi9Jv0QzSLl/dBi4xfC54CsmdXvhpR+8Jbp0yT6w1wd59kP9GDY1ll0DaqZaOgWrmHGmOw9a7jaf9Nkox14NGHlrGArIAv4IcHuJo12TMZyBgvh6A== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, 12 May 2026 21:59:26 +0800 Kefeng Wang wrote: > > > 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]， For other readers who may want to read the Sashiko review and might want to commeent, it is also available [1] at lore. > 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? Looks good to me, thank you! Could you send v2 with this change? > > Thanks. > > [1] > https://sashiko.dev/#/patchset/20260511132546.1973270-1-wangkefeng.wang@huawei.com?part=1 [1] https://lore.kernel.org/20260512052628.83798C2BCC7@smtp.kernel.org Thanks, SJ [...]