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AJvYcCU22T/sd6TYy51H/Gom/LNxoL6LtnwMHy7GFSS/AG8x4AVcvkHNdVIaMz3BZvMS7RBxWGa2ng1HWQ==@kvack.org X-Gm-Message-State: AOJu0Yw5yW1uzXVKpnVvIjnDMkm76bkz75o3u55cLDaIvzH7F+tVTKjB J+rZe1uz+N1xnHqFtZRImaOWrBwn0Q7OxoecLf6mbquSOuhDnpsJ+OViue6CgINmpXU+T/NJZsr Tx6UMPMjs6nEZry5wwqtt4uyQrrEvwsecoA4GVfsM X-Gm-Gg: ASbGncun1sB9KRsp/fgIvdhFQD5Iwt1iE3NUhP6gohkLorkToK6ocxOw9ZQad0W/0Wl Pg74XrInH2tSSYNSACLi5X6nBjZgagUezbj0CpYUJzgPrrk1FFR6b6e/FRop5jJx1sh65da+jeK hxjz+qeQSJHPYrvcrhsKDtPaq0Tkgff/0hOg4gGWhNqP/VaV8Kvy+JkFmf/cBOfecLMED2enufI +eJCTgwQ618x1nrpIaO2uyCWIIgB7MrQchOLfCxALgYNecaaHRf90ZSFA== X-Google-Smtp-Source: AGHT+IE2h8TSu1f2xlTHQNzRe2M4cO1d9LN+if2AzP4uw/DfT+W19/p6yOk0Sqok9Hqo2w25G9KQAq/6ayg8a1nUC9k= X-Received: by 2002:a50:875a:0:b0:621:dc0f:6b2c with SMTP id 4fb4d7f45d1cf-623d2c48760mr196588a12.1.1757396275344; Mon, 08 Sep 2025 22:37:55 -0700 (PDT) MIME-Version: 1.0 References: <20250908044950.311548-1-lokeshgidra@google.com> In-Reply-To: From: Lokesh Gidra Date: Mon, 8 Sep 2025 22:37:43 -0700 X-Gm-Features: Ac12FXyVeaDucZMYToF6VX-RqpdE93vDIHjv1pimD0yo8dr-BsQ83JAnCHeowxs Message-ID: Subject: Re: [RFC PATCH 1/2] mm: always call rmap_walk() on locked folios To: Barry Song <21cnbao@gmail.com> Cc: akpm@linux-foundation.org, linux-mm@kvack.org, kaleshsingh@google.com, ngeoffray@google.com, David Hildenbrand , Lorenzo Stoakes , Harry Yoo , Peter Xu , Suren Baghdasaryan , SeongJae Park Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 2BE1D160005 X-Stat-Signature: nqq8a4nd8p67d675pzq5crpa6a3hpkej X-Rspam-User: X-HE-Tag: 1757396276-793669 X-HE-Meta: U2FsdGVkX18finPiDQvn3qJAFrIDRVvif+cEc79w/f9FJxK2wnDuMG8ohZy9A2pAFU4lucdoKdowaNN92dIakL+GktIOY0kRGs3TC8Fti2S04xDkEZmoUfp3gWAhbI2N74Uv/kNbC1nxcWaqW50miDUw/sVeY+RwmWGaSuNAZ1uBmNDamAYS8sYLsvE8DXp8ZUKMWfWzSEyV8Pf3kduCQ/lRKV4ON0Z5bePgHxK98Ozr5GjOL24/pEa3jWWU4b6ABxm5cSe+EZJ+Pq7W2I2/O3/Pmy9Q8K9HviljiVMk2Y0KqtH08H4DdXNvSZzx4WobVgPNtddaONu5lm0I8YK3ZcKJ0K9zPALPPWqmHchzWHO3xrW6ljSBTKPTcXX4bym7Nkx3joErsxcEf0EW/JoVK7nerXIqAwME41EzSCO+Ku5eXZnwmsVpA4XkEz3PvnbJnUQ+0Ywxj6fxUK/LKE016/WrPD1FOdPIRTpi3FJAMPY8SaUBVOOLs2H/keiAsQ0vK6v372y2o0Y1S3mnUPm7JOv+ivvjBt0x4QWHWxh2hVjZYRZAOn68CCQSaK2mQdljXo3UQA4qvES/hizccyYV1zYPEdmKwnSzTCjGKl6YaPw2/p5T2/kq4vla9k3K9X55y6qFmD+sOP1EQmghIq36I/mlonMXJALUw4iRenQ/p/f/6Tapv2W2ghtsBcxzNBom/xbeVmH//B8Cd2M6b2aNdjtvkiHdfEk7IWS95VM7IhGKmMpn/9bfWIsNnMxcxP0djidY9CCLLbVFoZiI6SL7tOt8d591m5LiyU1O6DPZodgkAe6cqZ6zixpxaXw3QFpFYARW0LVxljfsnjtNoJYd0Ccx5BAsTGVw+B4ubi1c5+kUNzez60OzXGY1E2hNxyIg3siTzTSVP++67TqodXyfheHmmn2EAxoIS7jt/3HHuZP5Bmf6kQ4eehgVRwku7U1WanPU5oo5C5Np8RiiPxt xQkOGTs1 JspSsJftf9rKi2XSLtpB7sY4zZ4NPvPfbh5ea+NhHvgie0ghsDH+WF7NPd9ohkXH+8Rd02Ee0j+io6SwXsIEvU9CuU18S/P9xE/z+/kuk6EoYvLlXa3qnA4Zb145suIZG652DcM2P6jlDy9SWRydP1KmtmcEdVQnftmNx6rRpav6hNMJ9WF+ApJnuMJyfCVSyZR5EA68DI+phsN2X+Rq3N1U+63m232WDzst6seD6gLvL02hHFWbhUlbyK1CjzTUHKzq5LbW+3C81f6H7Ea25mhK6ES0prlcoi7GgL8QOyoPAmxjz7lGoEVFXfby8lkIgm8U1MswzlIzHs7g= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, 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 Mon, Sep 8, 2025 at 5:40=E2=80=AFPM Barry Song <21cnbao@gmail.com> wrote= : > > On Tue, Sep 9, 2025 at 6:12=E2=80=AFAM Lokesh Gidra wrote: > > > > On Mon, Sep 8, 2025 at 2:47=E2=80=AFPM Barry Song <21cnbao@gmail.com> w= rote: > > > > > > On Mon, Sep 8, 2025 at 12:50=E2=80=AFPM Lokesh Gidra wrote: > > > > > > > > Prior discussion about this can be found at [1]. > > > > > > > > rmap_walk() requires all folios, except non-KSM anon, to be locked.= This > > > > implies that when threads update folio->mapping to an anon_vma with > > > > different root (currently only done by UFFDIO MOVE), they have to > > > > serialize against rmap_walk() with write-lock on the anon_vma, hurt= ing > > > > scalability. Furthermore, this necessitates rechecking anon_vma whe= n > > > > pinning/locking an anon_vma (like in folio_lock_anon_vma_read()). > > > > > > > > This can be simplified quite a bit by ensuring that rmap_walk() is > > > > always called on locked folios. Among the few callers of rmap_walk(= ) on > > > > unlocked anon folios, shrink_active_list()->folio_referenced() is t= he > > > > only performance critical one. > > > > > > As I understand it, shrink_inactive_list() also invokes folio_referen= ced(). > > > Shouldn=E2=80=99t it be called just as often as shrink_active_list()? > > > > I'm only talking about those callers which call rmap_walk() without > > locking anon folio. The > > shrink_inactive_list()->folio_check_references()->folio_referenced() > > path that you are talking about always locks the folio. So the > > behavior in that case wouldn't change. > > Thanks for the clarification. Could you add a note about this if there > is a v2? > Certainly, will do. > > > > > > > > > > > shrink_active_list() doesn't act differently depending on what > > > > folio_referenced() returns for an anon folio. So returning 1 when i= t > > > > is contended, like in case of other folio types, wouldn't have any > > > > negative impact. > > > > > > A complaint was raised that the LRU could become slightly disordered: > > > https://lore.kernel.org/linux-mm/20240219141703.3851-1-lipeifeng@oppo= .com/ > > > > > > We can re-test to confirm if this is the case. > > The patch in the link you provided is suggesting to control try-lock > > for anon_vma lock. But here we are dealing with folio lock. Not sure > > if the ordering issue will be there in this case. > > Right. Not sure what percentage of folios will be contended; I assume > it is minor. Maybe you could share some data on this in a v2? Any suggestion on how (or which test/benchmark) would be good to gather data on this? IIUC, shink_active_list() doesn't behave any differently whether there is contention or not, except when it's an executable file folio. So I doubt such data would be any useful. Please correct me if I'm wrong. > > Thanks > Barry