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a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1771927823; bh=HLl0s56QthgFvq5ounX7gaoVLceVUg13LF70lAn+VcA=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=eUuT//x3T18L5U+IYW4yhBmaBd1Hs2QpYgo5OmQczVfNVug3MUE6iNZOvDyCDeD8g gC5xNPPkbEHkCXbqejzoqOW7jwa5C31ubtGYhOFUmDH+BPZxhqMvHjxdNvtkFu7jJx 1vnTa9atEQN4TvD+WtyLtsy0vCv3GWgDnoMWpdxFxbDlwmyN9Qe5U0SeHTgrSm3TCS GrcBvsCxn1SgvRRq/3L/7oK5mA+S3CdhoGpd7VtBgrCZIYF/A3GCF2cEIHcjYhy7hb muv5pUvzmiIBvv5v6RcD8Dt6o5RIwsxzDuAB7IzgEzBpvMSmNwsgM3/0A/RjVz4Fhj ZFWRHqNAfA1KQ== Message-ID: Date: Tue, 24 Feb 2026 11:10:19 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH mm-new v8 4/4] mm: khugepaged: skip lazy-free folios To: Barry Song <21cnbao@gmail.com> Cc: Vernon Yang , akpm@linux-foundation.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 References: <20260221093918.1456187-1-vernon2gm@gmail.com> <20260221093918.1456187-5-vernon2gm@gmail.com> <658903fb-cf3a-43c3-b8c0-d47b63d10782@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 8bit X-Stat-Signature: c8zawcs9x94b955jezqdmeoyzpfu4uyj X-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 6C90240010 X-HE-Tag: 1771927824-689966 X-HE-Meta: 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 cMjKWcBn Z2qumq8qBtQuOA8MdXf7BXXsGo2+GEbQXI7HV0SRSt91P3kA65PzK4B6hTLgsmmzR0lxWkvcHRzJpXPaw+k9WzhorH4hswdqKSEDrMo7XUmeHztiJjNKSyih0u7gG9XdJSU6FeQGTkIsl7zxCmf6tmn6g7JJD5dMAaR9/9qhA/Av0TZ1j/n463cHQ8swxK947I591PiarRnYMIMsIJU1X536l3Ukc+HyIrxjS3hlnQyt/kjz0Wka/CqUulofElsW8UXXQEv89WSyWEFwcgYnJ6XIR4mgTCBT+Q/Lao5pT1hq5+1DZsqfbwOEr8Q== 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 2/23/26 21:08, Barry Song wrote: > On Mon, Feb 23, 2026 at 9:16 PM David Hildenbrand (Arm) > wrote: >> >> On 2/21/26 14:38, Vernon Yang wrote: >>> >>> 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 property. >>> The above commit log clearly states "all folios in VM_DROPPABLE are lazyfree" >>> ^^^^^^^^^^^^^^^ >>> (the "if" is redundant and should be removed), not "all folios are lazyfree". >> >> >> Exactly. folio_add_new_anon_rmap() makes sure that all folios (except >> the shared zero folios ;) ) in VM_DROPPABLE are lazyfree. >> >> In fact, MADV_FREE should be a NOP on VM_DROPPABLE, as >> folio_mark_lazyfree() doesn't do anything. >> > > Maybe we could do something like the following? > > diff --git a/mm/madvise.c b/mm/madvise.c > index c0370d9b4e23..173b0e5308b5 100644 > --- a/mm/madvise.c > +++ b/mm/madvise.c > @@ -817,6 +817,11 @@ static int madvise_free_single_vma(struct > madvise_behavior *madv_behavior) > range.end = min(vma->vm_end, end_addr); > if (range.end <= vma->vm_start) > return -EINVAL; > + > + /* All folios in the VM_DROPPABLE VMA are already lazyfree */ > + if (vma->vm_flags & VM_DROPPABLE) > + return 0; We could, but it feels like optimizing for a case that likely nobody triggers :) -- Cheers, David