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Wed, 21 Feb 2024 23:51:41 -0800 (PST) MIME-Version: 1.0 References: <20240129054551.57728-1-ioworker0@gmail.com> In-Reply-To: From: Lance Yang Date: Thu, 22 Feb 2024 15:51:29 +0800 Message-ID: Subject: Re: [PATCH 1/1] mm/khugepaged: bypassing unnecessary scans with MMF_DISABLE_THP check To: akpm@linux-foundation.org Cc: mhocko@suse.com, zokeefe@google.com, david@redhat.com, songmuchun@bytedance.com, shy828301@gmail.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: 182C640005 X-Rspam-User: X-Stat-Signature: 8b7xahs35k6c8i5yeci1tm4jc8imz8hw X-Rspamd-Server: rspam01 X-HE-Tag: 1708588301-41840 X-HE-Meta: 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 HdHWdf0H W2pZF4ZUOMsCbnoaeJeWVdIN8ZwJ2Kf3HB5iNHggMQro5WsVLcGJYLCW6R31BXDdX4fCUzBp4iqYgRMNPxF8p9ECjAw== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000564, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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. Best, Lance On Wed, Jan 31, 2024 at 5:30=E2=80=AFPM Lance Yang wr= ote: > > 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