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AJvYcCVILi/vsAs1RdExw3B8ecXn1BrpGma8BBcCUm6xZV8nh8D9GWZu7iEdl14ijaF1Gl/eZ+AOohLqfh293pQ5+VBNqT8= X-Gm-Message-State: AOJu0YwqpeJVLkfehYaL42NpeF+nypi0D+PZxRaP2tAC7n/54DIPtSjR 6FE9IqdJ/+oETv0oIkOrFOQrvZIlL0LDfssGHaDhqVTLiWmaDzMsKlNXWlQqTf+BMrJ1K8aMHzY jpUmbkhZEgsft6SmqtaKdhwaDcII= X-Google-Smtp-Source: AGHT+IGpZlkojZBuQ5KldQ9ONWwa0S0G4VmAypoUsFHq2B8Mwk1MF1kK5xY+uEXuh6dMkcAp3ymzBoFW3a5ZevC4SWA= X-Received: by 2002:a05:6902:1b85:b0:dcf:30d9:1d7b with SMTP id ei5-20020a0569021b8500b00dcf30d91d7bmr1453488ybb.45.1708675159252; Thu, 22 Feb 2024 23:59:19 -0800 (PST) MIME-Version: 1.0 References: <20240129054551.57728-1-ioworker0@gmail.com> <20240222131151.4d24563d58240e76a3b535db@linux-foundation.org> In-Reply-To: <20240222131151.4d24563d58240e76a3b535db@linux-foundation.org> From: Lance Yang Date: Fri, 23 Feb 2024 15:59:07 +0800 Message-ID: Subject: Re: [PATCH 1/1] mm/khugepaged: bypassing unnecessary scans with MMF_DISABLE_THP check To: Andrew Morton , Yang Shi Cc: 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: 4EB7E4000D X-Rspam-User: X-Rspamd-Server: rspam11 X-Stat-Signature: 3bc4owwh4gjxqynijtgehf1ckm5n3aqz X-HE-Tag: 1708675160-164251 X-HE-Meta: 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 iCnKF7UX D3fBML747U4M41WiMGrbmzQMFnw2YvcOvVDmmAzN2EP4AA5vF8PFRGRQgyKKkBixaT2HPfzjuuexc5vzgLwzy7eUH7Ty4whug/kIHXQtYLeNZfe6lq6nOCGnLivhe8sQR2cwx/4P6vtysyxh8Fy8GaN4xjXGt0pVG0qNI54PB7BjAdaz7mlNC3vmN4nIu0/zPuiZ7NGw9Vf5aTtZLQZ58vpBudDn1KkRzYlWHKjaFU0PJc6/j43A7bGJqS+spYhxwOAX8QnX3sWqA+mU4SKnu889X41mde9RHDVfFx13iZQBXQ5XxZh4LQ6ESchn+/hkaRw64NSYO2kKJji0D9aqGDvkTQD4ovqyWY49pH+VxpzzonTt6v051vd+CeJg+EEme6RH3ZX4cvif4y4i4kM1UrZres8uL3cvRK0iUSH8MXREths8fXAxHSDCDjOUsQcFHx766Iz2fggquXjhekmySsJPYwi3KmSVHjKPHF50RcX5uZPU= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000077, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Thanks for taking the time to look into this! Thanks, Yang and Andrew! Best, Lance On Fri, Feb 23, 2024 at 5:11=E2=80=AFAM Andrew Morton wrote: > > On Thu, 22 Feb 2024 12:23:21 -0800 Yang Shi wrote: > > > > 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? > > I added it. > > --- a/txt/mm-khugepaged-bypassing-unnecessary-scans-with-mmf_disable_thp-= check.txt > +++ b/txt/mm-khugepaged-bypassing-unnecessary-scans-with-mmf_disable_thp-= check.txt > @@ -9,6 +9,24 @@ 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. > > +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% > + > +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. > + > This commit introduces a check before each scanning process to test the > MMF_DISABLE_THP flag for the given mm; if the flag is set, the scanning > process is bypassed, thereby improving the efficiency of khugepaged. >