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Mon, 23 Feb 2026 12:11:00 -0800 (PST) MIME-Version: 1.0 References: <20260221093918.1456187-1-vernon2gm@gmail.com> <20260221093918.1456187-5-vernon2gm@gmail.com> In-Reply-To: From: Barry Song <21cnbao@gmail.com> Date: Tue, 24 Feb 2026 04:10:47 +0800 X-Gm-Features: AaiRm51lMvgsh7oDD5pQgGtSV5Y_M7Clbu2jPHQRGC9KNFInsWHaPcK8fDzJr0g Message-ID: Subject: Re: [PATCH mm-new v8 4/4] mm: khugepaged: skip lazy-free folios To: Vernon Yang Cc: akpm@linux-foundation.org, david@kernel.org, lorenzo.stoakes@oracle.com, ziy@nvidia.com, dev.jain@arm.com, lance.yang@linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Vernon Yang Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-HE-Meta: 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 0e4uDClp UhuVnGguQeoSe38/0Ki/eNAZEhgkqguJt/Mp1+cZfV6ZoxER27nuO+qokOG9nBCawSj7Flkzx1qVH11mbICjY00WXff0Dp+dS/4YmicPLHVZIhXymijPfRQt0lr++x0g8hzxRq5xHIXumZPWN6OQPD1y+yH3kBtfaQ390HD3yHrhF/JGIEBVF0Df4ZXfy5jp6xBvyWVo84NswwAY1FSsgHxXhO8LJvSHS4SvzNivRobaO+OfD1xnbxkc1TvnaTvcYCGQL+VXITyVEEmv09sk5ZqxXSVKFj/+AXxmL2BqQoKy+HBpoH++n/hAFeVoZNEyoS+PpFmxEPaZrjTlVXo6anm+4F7gq8KwfCtAyhQSz4T+2CZZ+b3eP9vXcKIkTVfawyoE+8O+v9ozy1kjuG893xiSyI7VHFmuVX9EKJU7z8mTXqPw= X-Rspamd-Queue-Id: 04FFA180016 X-Stat-Signature: 83usfqazjgzut4kcg65kf4c9o7awbewy X-Rspam-User: X-Rspamd-Server: rspam12 X-HE-Tag-Orig: 1771877461-490113 X-HE-Tag: 1771877463-816224 X-HE-Meta: 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 Kf6Ctfry Wocge+thN0DYYhWoJH91x6PoDZ4s51M17ZOwvfY5bewjZi0uaENuq5J8gP5ISl/6hy92axiDUWEeVzclYL6TGepF7g5Mwzc7WwEi7NcDc6li6/QXptUAznwRpRIMoS83fiI4lMCs78VN6KvtCPJdnvP/+iGQNqxGyX26YSHAurwgePo7YDIShdTfKlG4RjiI8sSZ34JWA8+E6bmreuGYsjVTC3GtS4LE1EDXwMaOisBcAbl/d3DM03cAew/43ZZ92SGNt 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 Sat, Feb 21, 2026 at 9:39=E2=80=AFPM Vernon Yang w= rote: > > On Sat, Feb 21, 2026 at 06:27:36PM +0800, Barry Song wrote: > > On Sat, Feb 21, 2026 at 5:40=E2=80=AFPM Vernon Yang wrote: > > > > > > From: Vernon Yang > > > > > > For example, create three task: hot1 -> cold -> hot2. After all three > > > task are created, each allocate memory 128MB. the hot1/hot2 task > > > continuously access 128 MB memory, while the cold task only accesses > > > its memory briefly and then call madvise(MADV_FREE). However, khugepa= ged > > > still prioritizes scanning the cold task and only scans the hot2 task > > > after completing the scan of the cold task. > > > > > > And if all folios in VM_DROPPABLE are lazyfree, Collapsing maintains > > > that property, so we can just collapse and memory pressure in the fut= ure > > > > I don=E2=80=99t think this is accurate. A VMA without VM_DROPPABLE > > can still have all folios marked as lazyfree. Therefore, having > > all folios lazyfree is not the reason why collapsing preserves > > the property. > > In folio_add_new_anon_rmap(), we know that the vma has the VM_DROPPABLE > attribute, which is the root reason why Collapsing maintains that propert= y. > The above commit log clearly states "all folios in VM_DROPPABLE are lazyf= ree" > ^^^^^^^^^^^^^^^ > (the "if" is redundant and should be removed), not "all folios are lazyfr= ee". Yes, we should remove the if; otherwise, it=E2=80=99s misleading. [...] > > > > I would prefer to add a comment about VM_DROPPABLE here > > rather than only mentioning it in the changelog. > > Is the following comment clear? > > /* > * If the vma has the VM_DROPPABLE flag, the collapse will > * preserve the lazyfree property without needing to skip. > */ Looks good to me. Best Regards Barry