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Sun, 08 Feb 2026 05:26:30 -0800 (PST) MIME-Version: 1.0 References: <20260207081613.588598-1-vernon2gm@gmail.com> <20260207081613.588598-5-vernon2gm@gmail.com> In-Reply-To: From: Vernon Yang Date: Sun, 8 Feb 2026 21:26:19 +0800 X-Gm-Features: AZwV_Qjnb0hrc_baMl-CLvkEWHGx7wjBdz6lnXFtS2sh5f8ZrwO-GYDrBRG7K0c Message-ID: Subject: Re: [PATCH mm-new v7 4/5] mm: khugepaged: skip lazy-free folios To: "David Hildenbrand (Arm)" Cc: Barry Song <21cnbao@gmail.com>, Lance 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-Rspamd-Server: rspam11 X-Stat-Signature: s7zuqor361gc1336qmjuccgsw3usis1t X-Rspam-User: X-Rspamd-Queue-Id: 449E712000A X-HE-Tag: 1770557192-829620 X-HE-Meta: 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 4TwS8slc 1KROIqINX4LPZ9x1D7HJIRKT+1AOVf15kJwdBI9b18/DEIeJ7wb6JIEFDZlm8scW4rg6NkUnC2aV/+B0llTCXTTl10Nsv0zz3V5+ptfbUVjd9VNVDX/UfE+kHmu7FZ1OZEZFByKW8BvUX4+M3aKlra8/NfPUmFvEUR0yEBPB3623RftkRxJkj5zTkzndtOP7F3uZkc0SabpC3gUTg3hanF/GisF2P0Gi4xg82s+KUB1K4MbrQj5VSlLwArxhZGpEAGvZ4vzkwtm91mCYjo07pR7Ce5mkgpNf8F7UV2PbKQ7a5PjP37q7I+kK1ibCOrhen3VcXOzI56hvGOcgGmYSxGg8LsDiEH7nNyUtPbMnpAwiv2lXb0WvqxBabCAoVfirrC7julGwC+dcSOFwhIB7iqUBKVJyZA05RPNB6RUOh8TOiNJU= 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. Thank you Barry for pointing out this corner case, and thank you David for suggestions and explanations. LGTM, I will fix it in the next version. --- Thanks, Vernon