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AJvYcCXzO6+iWA47bQOqK7F0Npw/nrG62LGgWXstYTe/CBA8Db1yIvApWiMqJlvYHo7RPN3utCcDcElCm1Wa1soVzoSZdZ8= X-Gm-Message-State: AOJu0Yz38v/p2pxN/hjD9fUgSWipcVOY1WgvRqcRfPCJryrIfi3haxfc T5nWTw5SxcNMurQZE6jAzidRe+YScgtg0MPZ3naTNeTDPSSdvf5O71JhVBuMDNW6EPFmyNmDays DKdBjXUytoKvf9c8JuW3GJ0MVyOc= X-Google-Smtp-Source: AGHT+IEYlyvmciMoWJ2MEC+vVPayK8seyKA+JhIYdvSeWsSf/2H2RqRaxwur2uqaxKGel2jPOVp8zUj+CrLX0nG0JUU= X-Received: by 2002:a17:90b:b01:b0:29a:4300:e2c with SMTP id bf1-20020a17090b0b0100b0029a43000e2cmr3476015pjb.34.1708633413413; Thu, 22 Feb 2024 12:23:33 -0800 (PST) MIME-Version: 1.0 References: <20240129054551.57728-1-ioworker0@gmail.com> In-Reply-To: From: Yang Shi Date: Thu, 22 Feb 2024 12:23:21 -0800 Message-ID: Subject: Re: [PATCH 1/1] mm/khugepaged: bypassing unnecessary scans with MMF_DISABLE_THP check To: Lance Yang Cc: akpm@linux-foundation.org, mhocko@suse.com, zokeefe@google.com, david@redhat.com, songmuchun@bytedance.com, peterx@redhat.com, minchan@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: 9ECB340015 X-Rspam-User: X-Stat-Signature: 9ofn5dwjowba14zzhpch16uprtfmzux1 X-Rspamd-Server: rspam03 X-HE-Tag: 1708633414-958628 X-HE-Meta: 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 Y9hX5oXI T+DnadNFNkEK/oIZb2Zukjr2dLKr+O1Yh9ZS9O/V+hXIv8ff41v7NB8z4BmC0QN+/CS5RzJOyIj02WiEyzTEctsbdVDaICqzz23WB6BMGmKW+PI0yT+M3In2K3bm1we9hB0OIMpcmk4mwvF5TQPAcQH36wPBswtdXbCza3rkab0yNvQ/ekuPivWqpXCGsUU57iMKwHz8Y0AbHlYjd+6GTWHEk+LphqIJyJXWK2+76bFEifmKg49UsLJOj+eGmK8t/E4Cq9WziRf5YSvyEyVE7ZvfS3jO67TRnFJiJmJJR9muX6HYtQj54LEmKMVUybwNxQWFv9g5mtTjAZM2cEWgOl990aDo4CRI8yP5FZqWfJdrBuC4owEtH+jKavnI3ffOuWiZGc58UcqxBHRjw1ZX0DggTF5CcsTcOzaMKRmd6X8OUxKXYEEKFayMZ3pbu8xa1lT0bJee6rT2Qh2g= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000019, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Feb 21, 2024 at 11:51=E2=80=AFPM Lance Yang w= rote: > > Hey, > > On an Intel Core i5 CPU, the time taken by > khugepaged to scan the address space of > the process, which has been set with the > MMF_DISABLE_THP flag after being added > to the mm_slots list, is as follows (shorter is better): > > VMA Count | Old | New | Change > --------------------------------------- > 50 | 23us | 9us | -60.9% > 100 | 32us | 9us | -71.9% > 200 | 44us | 9us | -79.5% > 400 | 75us | 9us | -88.0% > 800 | 98us | 9us | -90.8% > > IIUC, once the count of VMAs for the process > exceeds page_to_scan, khugepaged needs to > wait for scan_sleep_millisecs ms before scanning > the next process. IMO, unnecessary scans could > actually be skipped with a very inexpensive > mm->flags check in this case. Thanks for following up on this, can you please capture all the information in the commit log? > > Best, > Lance > > On Wed, Jan 31, 2024 at 5:30=E2=80=AFPM Lance Yang = wrote: > > > > Updating the change log. > [...] > > > On Mon, Jan 29, 2024 at 1:46=E2=80=AFPM Lance Yang wrote: > > > > > > khugepaged scans the entire address space in the > > > background for each given mm, looking for > > > opportunities to merge sequences of basic pages > > > into huge pages. However, when an mm is inserted > > > to the mm_slots list, and the MMF_DISABLE_THP flag > > > is set later, this scanning process becomes > > > unnecessary for that mm and can be skipped to avoid > > > redundant operations, especially in scenarios with > > > a large address space. > [...] > > > Signed-off-by: Lance Yang