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Howlett" , Vlastimil Babka , Suren Baghdasaryan , Pedro Falcato , Ryan Roberts , Harry Yoo , Jann Horn , Chris Li , Barry Song Date: Sun, 03 May 2026 14:26:36 -0400 In-Reply-To: References: Autocrypt: addr=riel@surriel.com; prefer-encrypt=mutual; keydata=mQENBFIt3aUBCADCK0LicyCYyMa0E1lodCDUBf6G+6C5UXKG1jEYwQu49cc/gUBTTk33A eo2hjn4JinVaPF3zfZprnKMEGGv4dHvEOCPWiNhlz5RtqH3SKJllq2dpeMS9RqbMvDA36rlJIIo47 Z/nl6IA8MDhSqyqdnTY8z7LnQHqq16jAqwo7Ll9qALXz4yG1ZdSCmo80VPetBZZPw7WMjo+1hByv/ lvdFnLfiQ52tayuuC1r9x2qZ/SYWd2M4p/f5CLmvG9UcnkbYFsKWz8bwOBWKg1PQcaYHLx06sHGdY dIDaeVvkIfMFwAprSo5EFU+aes2VB2ZjugOTbkkW2aPSWTRsBhPHhV6dABEBAAG0HlJpayB2YW4gU mllbCA8cmllbEByZWRoYXQuY29tPokBHwQwAQIACQUCW5LcVgIdIAAKCRDOed6ShMTeg05SB/986o gEgdq4byrtaBQKFg5LWfd8e+h+QzLOg/T8mSS3dJzFXe5JBOfvYg7Bj47xXi9I5sM+I9Lu9+1XVb/ r2rGJrU1DwA09TnmyFtK76bgMF0sBEh1ECILYNQTEIemzNFwOWLZZlEhZFRJsZyX+mtEp/WQIygHV WjwuP69VJw+fPQvLOGn4j8W9QXuvhha7u1QJ7mYx4dLGHrZlHdwDsqpvWsW+3rsIqs1BBe5/Itz9o 6y9gLNtQzwmSDioV8KhF85VmYInslhv5tUtMEppfdTLyX4SUKh8ftNIVmH9mXyRCZclSoa6IMd635 Jq1Pj2/Lp64tOzSvN5Y9zaiCc5FucXtB9SaWsgdmFuIFJpZWwgPHJpZWxAc3VycmllbC5jb20+iQE +BBMBAgAoBQJSLd2lAhsjBQkSzAMABgsJCAcDAgYVCAIJCgsEFgIDAQIeAQIXgAAKCRDOed6ShMTe g4PpB/0ZivKYFt0LaB22ssWUrBoeNWCP1NY/lkq2QbPhR3agLB7ZXI97PF2z/5QD9Fuy/FD/jddPx KRTvFCtHcEzTOcFjBmf52uqgt3U40H9GM++0IM0yHusd9EzlaWsbp09vsAV2DwdqS69x9RPbvE/Ne fO5subhocH76okcF/aQiQ+oj2j6LJZGBJBVigOHg+4zyzdDgKM+jp0bvDI51KQ4XfxV593OhvkS3z 3FPx0CE7l62WhWrieHyBblqvkTYgJ6dq4bsYpqxxGJOkQ47WpEUx6onH+rImWmPJbSYGhwBzTo0Mm G1Nb1qGPG+mTrSmJjDRxrwf1zjmYqQreWVSFEt26tBpSaWsgdmFuIFJpZWwgPHJpZWxAZmIuY29tP okBPgQTAQIAKAUCW5LbiAIbIwUJEswDAAYLCQgHAwIGFQgCCQoLBBYCAwECHgECF4AACgkQznneko TE3oOUEQgAsrGxjTC1bGtZyuvyQPcXclap11Ogib6rQywGYu6/Mnkbd6hbyY3wpdyQii/cas2S44N cQj8HkGv91JLVE24/Wt0gITPCH3rLVJJDGQxprHTVDs1t1RAbsbp0XTksZPCNWDGYIBo2aHDwErhI omYQ0Xluo1WBtH/UmHgirHvclsou1Ks9jyTxiPyUKRfae7GNOFiX99+ZlB27P3t8CjtSO831Ij0Ip QrfooZ21YVlUKw0Wy6Ll8EyefyrEYSh8KTm8dQj4O7xxvdg865TLeLpho5PwDRF+/mR3qi8CdGbkE c4pYZQO8UDXUN4S+pe0aTeTqlYw8rRHWF9TnvtpcNzZw== Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.56.2 (3.56.2-2.fc42) MIME-Version: 1.0 X-Stat-Signature: qtrqq1etdfrubt86shzdc67zmrw8xmgi X-Rspam-User: X-Rspamd-Queue-Id: 0F5DB4000D X-Rspamd-Server: rspam07 X-HE-Tag: 1777832822-128300 X-HE-Meta: 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 28pcELNb 5I/KBSqdQGyCMAughmOw4hXrUveLW6qyZOmxo++kBA0+dEGJwDGD1yyEZwIdmn4SQdr3kSbhz1zrT4YrmmYRbxSRH4z2euxXm40UvQMjzEWIUAhOATf0ay5pY5szd8VEInYmOTYojaAXC217+dsf2OF/rhwCYa1Se1Z/sfO2E53xSxj2iHPBHUZIXgh3ES/KHuIiEf3YLgSAh+P15SoJKKtfYJjeQ1x4Hwjbqy7n+G6LwomHeJOT7P83zhw== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Sat, 2026-05-02 at 07:53 +0100, Lorenzo Stoakes wrote: > As is time-honoured LSF tradition, I am sharing code for my proposal. >=20 > I worked a very long day yesterday and got the _very_ rough PoC code > into > some kind of vaguely shareable state. >=20 > https://git.kernel.org/pub/scm/linux/kernel/git/ljs/linux.git/log/?h=3Dpr= oject/cow-context >=20 > CAVEATS: >=20 > * The code is not great, it's 'experimental, wave your arms, hope for > the > =C2=A0 best' stuff used for experimentation. First, some refcounting that confuses me. The changelog, and the code in dup_cow_context shows that only the parent's cow context gets an increased refcount. However, the code in __put_cow_context seems to unconditionally decrement refcounts all up the hierarchy, instead of bailing out once it encounters a parent that still has a non-zero refcount. How is that supposed to work? Now, having the remaps array cloned at fork time does make the refcounting on that side a lot simpler. I like that. However, it does raise another question. Say we have process A, with child process B. Process A has memory mapped at address X. Process B munmaps memory at address X, and then maps new memory at address X. If I haven't missed something important,=C2=A0the remap table does not need to get used, because=C2=A0 the offset and the virtual address match. How does the COW walk handle that situation? Overall, I like that you are trying to tackle the problems associated with anon_vma, but have to wonder if this implementation will be able to avoid some of the complexity=20 inherent in the problem space. --=20 All Rights Reversed.