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AJvYcCWTo8iG0naCrHcmDQwvel5eE/1n5/MzGc9I62lIWdpBK/Q7ybOIUYGh9PfUH2Jlk6wcGQOSOGUGjg==@kvack.org X-Gm-Message-State: AOJu0YxS03UaUD/ClSzVdW98uEMtG3VF+QcZpNjunS/k0h28pdTrArwQ w3vrg9w0EOtynkwZtQk1Mv0S7jBjEl8pufkZd6NU9EN2ApJCFRKD9tup7VG2up5VYvS+96TodmN 5VBGnE9x4zAbumhi2gMT/oJFK7jM09tQ= X-Gm-Gg: AZuq6aIf7gmYUknCBm7oZ0oS/fa5Mp2ZiMPNc6xVZjzebxf3ToAlRU33Ehz0CBLvg2t spdQ/Cp+RwLaDFnvCzjlF8ixFUEup5yK6tTGXzyyjwlfa2JDMi418IjHR/hSGlFj0OWAWEg6tdU WYkwPXSX63LS0nM1rkzD8PG+sI42ilVzU/0S2+jbJLG/xonPskTWdLkkazVGdFW9duxhIgELMpa JoQAelI139VYadtFjkhEFYXee7drnScqoTKvX/BSBmRUDtf4hbb/RBTnEYW+EMzXb/OIA== X-Received: by 2002:a05:6214:e6c:b0:88f:d4b1:4c2d with SMTP id 6a1803df08f44-8953cd995b2mr98440976d6.60.1770503511579; Sat, 07 Feb 2026 14:31:51 -0800 (PST) MIME-Version: 1.0 References: <20260207081613.588598-1-vernon2gm@gmail.com> <20260207081613.588598-5-vernon2gm@gmail.com> In-Reply-To: From: Barry Song <21cnbao@gmail.com> Date: Sun, 8 Feb 2026 06:31:40 +0800 X-Gm-Features: AZwV_QgxhNqRogNl6N9SKbBz4-2j5TRyVujP-FCTMTWOGQJSFKVLI-AR7kj7ONU Message-ID: Subject: Re: [PATCH mm-new v7 4/5] mm: khugepaged: skip lazy-free folios To: "David Hildenbrand (Arm)" Cc: Lance Yang , Vernon Yang , akpm@linux-foundation.org, lorenzo.stoakes@oracle.com, ziy@nvidia.com, dev.jain@arm.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Vernon Yang Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: D0909A0004 X-Stat-Signature: hez9f9f4knek7osgerf8ucs9j9n41bxs X-HE-Tag: 1770503512-758917 X-HE-Meta: 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 oOlge9St ApsDfa99ttAFSRUbfdu5YlK8uH2N5SFUNDzRwf2/FeGNDRUWsCFtAZzYKn/NIGZ8+iePSWwaLYsSS5+ayhdjCuNcBiesISgX4SHAGFzfJR0gPo5ZFA307BRa/YoDOU/43FwXBYxgU3S3+iCaMTbwL41j4nKjlnUKSdMzJaB906rniou02BfUtf7ABc8wZdlWUD3Ldfhvvd++da73wc7TlsuB8Ajx0QK8LwXXsqRMu/uDs2IwuBCkohDfjFnMTIe24o682j1rTiB6unpaSRZ9RDl7QQ499/gut5xFjLUBn65bSJRnvzA5ElvTQMYfIHp6s72h+v6gWcYds3fJYU+4xRDQefjaJhxzQDnN3qH1MBr6u/MDTjFjH0awf7aE0iHAkq7I3Pujqqt/iQT6u6BTFw4UJ26pAIPEUYAAU5tZTNva/PRg= 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 Sun, Feb 8, 2026 at 6:25=E2=80=AFAM David Hildenbrand (Arm) wrote: > > On 2/7/26 23:17, Barry Song wrote: > > On Sun, Feb 8, 2026 at 6:05=E2=80=AFAM David Hildenbrand (Arm) wrote: > >> > >> On 2/7/26 23:01, Barry Song wrote: > >>> > >>> Maybe change =E2=80=9Cjust not skip=E2=80=9D to =E2=80=9Cjust skip=E2= =80=9D? > >>> > >>> If the goal is to avoid the collapse overhead for folios that are > >>> about to be dropped, we might consider skipping collapse for the > >>> entire VMA=EF=BC=9F > >> If there is no memory pressure in the system, why wouldn't you just wa= nt > >> to collapse in a VM_DROPPABLE region? > >> > >> "about to be dropped" only applies once there is actual memory pressur= e. > >> If not, these pages stick around forever. > > > > agree. But this brings us back to the philosophy of the original patc= h. > > If there is no memory pressure, lazyfree folios won=E2=80=99t be droppe= d, so > > collapsing them might also be reasonable. > > It's about memory pressure in the future. > > > > > Just collapsing fully lazyfree folios with VM_DROPPABLE while > > skipping partially lazyfree VMAs seems a bit confusing to me :-) > > Think of it like this: > > All folios in VM_DROPPABLE are lazyfree. Collapsing maintains that > property. So you can just collapse and memory pressure in the future > will free it up. > > In contrast, collapsing in !VM_DROPPABLE does not maintain that > property. The collapsed folio will not be lazyfree and memory pressure > in the future will not be able to free it up. Thanks for the clarification. I agree with your point =E2=80=94 whether laz= yfree folios are carried over to the new folios changes the whole story. Best Regards Barry