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b=A8kA9PWJsKdpYQ2CpBqzkOfqBwEeEF4/2ZT4gBaEtbBfff2ixrbCh57x0BX3PL1Q/ LRcsPWqd+g4xHYH+APQddZHFzqVWwZtUGJUL2ugp7dNJ1M1NQ0kWAey74Ljdd8rPfU ZvXvt45+3GFJD7X0CdQALwh2fmjLib0nmKVV44Q/jVNYJ91jBDD1ekyWQYEPwFNhRr J4nVEA23qJollhtoj3dgmfuLPd4lPGfQRvyFL4gH+tTmPZ1S4lMR6JZk2fC2OZNJqo DYuErBJZvCnW6V2ChlHm3UiUC2OzRxbT3tqer9lZp7wib/mCTkg6T5qSjex029nZPr /XWqER5/3Pu+A== From: Pratyush Yadav To: Mike Rapoport Cc: Jason Gunthorpe , Pasha Tatashin , pratyush@kernel.org, jasonmiu@google.com, graf@amazon.com, changyuanl@google.com, dmatlack@google.com, rientjes@google.com, corbet@lwn.net, rdunlap@infradead.org, ilpo.jarvinen@linux.intel.com, kanie@linux.alibaba.com, ojeda@kernel.org, aliceryhl@google.com, masahiroy@kernel.org, akpm@linux-foundation.org, tj@kernel.org, yoann.congal@smile.fr, mmaurer@google.com, roman.gushchin@linux.dev, chenridong@huawei.com, axboe@kernel.dk, mark.rutland@arm.com, jannh@google.com, vincent.guittot@linaro.org, hannes@cmpxchg.org, dan.j.williams@intel.com, david@redhat.com, joel.granados@kernel.org, rostedt@goodmis.org, anna.schumaker@oracle.com, song@kernel.org, zhangguopeng@kylinos.cn, linux@weissschuh.net, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-mm@kvack.org, gregkh@linuxfoundation.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, rafael@kernel.org, dakr@kernel.org, bartosz.golaszewski@linaro.org, cw00.choi@samsung.com, myungjoo.ham@samsung.com, yesanishhere@gmail.com, Jonathan.Cameron@huawei.com, quic_zijuhu@quicinc.com, aleksander.lobakin@intel.com, ira.weiny@intel.com, andriy.shevchenko@linux.intel.com, leon@kernel.org, lukas@wunner.de, bhelgaas@google.com, wagi@kernel.org, djeffery@redhat.com, stuart.w.hayes@gmail.com, lennart@poettering.net, brauner@kernel.org, linux-api@vger.kernel.org, linux-fsdevel@vger.kernel.org, saeedm@nvidia.com, ajayachandra@nvidia.com, parav@nvidia.com, leonro@nvidia.com, witu@nvidia.com Subject: Re: [PATCH v3 29/30] luo: allow preserving memfd In-Reply-To: References: <20250807014442.3829950-1-pasha.tatashin@soleen.com> <20250807014442.3829950-30-pasha.tatashin@soleen.com> <20250826162019.GD2130239@nvidia.com> Date: Mon, 01 Sep 2025 19:01:38 +0200 Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 Content-Type: text/plain X-Rspamd-Queue-Id: 50F8440018 X-Rspam-User: X-Stat-Signature: rdq3bnoae8g5gimbs1smoe3ed7kzj71i X-Rspamd-Server: rspam09 X-HE-Tag: 1756746111-998018 X-HE-Meta: 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 WIPyoxLe +zXRsaNLV8QpFpTCCik+N+GvxWzlBxlHwFxqwVToxiVlt2dSLD5srj/ZuqH13nMKYLFr/SApiN5kZN7XEhU/TOhXpTaIBj0sX98CfwZhkldNZEnwHLVEXwUCPQuMIp2OU4jjI8WWbC9iBnGw402v55zk7WuNgYYek+us5O9HZiD8L7wz574WW7+y360c/dnbvtk5cyC50EYnAJGbvhUAFt6xYZCkAl1NeDFJhaPgIR9XbhylM0busulY1XoFK2wR0cyck+r/2l0jTLLk= 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: Hi Mike, On Mon, Sep 01 2025, Mike Rapoport wrote: > On Tue, Aug 26, 2025 at 01:20:19PM -0300, Jason Gunthorpe wrote: >> On Thu, Aug 07, 2025 at 01:44:35AM +0000, Pasha Tatashin wrote: >> >> > + /* >> > + * Most of the space should be taken by preserved folios. So take its >> > + * size, plus a page for other properties. >> > + */ >> > + fdt = memfd_luo_create_fdt(PAGE_ALIGN(preserved_size) + PAGE_SIZE); >> > + if (!fdt) { >> > + err = -ENOMEM; >> > + goto err_unpin; >> > + } >> >> This doesn't seem to have any versioning scheme, it really should.. >> >> > + err = fdt_property_placeholder(fdt, "folios", preserved_size, >> > + (void **)&preserved_folios); >> > + if (err) { >> > + pr_err("Failed to reserve folios property in FDT: %s\n", >> > + fdt_strerror(err)); >> > + err = -ENOMEM; >> > + goto err_free_fdt; >> > + } >> >> Yuk. >> >> This really wants some luo helper >> >> 'luo alloc array' >> 'luo restore array' >> 'luo free array' > > We can just add kho_{preserve,restore}_vmalloc(). I've drafted it here: > https://git.kernel.org/pub/scm/linux/kernel/git/rppt/linux.git/log/?h=kho/vmalloc/v1 > > Will wait for kbuild and then send proper patches. I have been working on something similar, but in a more generic way. I have implemented a sparse KHO-preservable array (called kho_array) with xarray like properties. It can take in 4-byte aligned pointers and supports saving non-pointer values similar to xa_mk_value(). For now it doesn't support multi-index entries, but if needed the data format can be extended to support it as well. The structure is very similar to what you have implemented. It uses a linked list of pages with some metadata at the head of each page. I have used it for memfd preservation, and I think it is quite versatile. For example, your kho_preserve_vmalloc() can be very easily built on top of this kho_array by simply saving each physical page address at consecutive indices in the array. The code is still WIP and currently a bit hacky, but I will clean it up in a couple days and I think it should be ready for posting. You can find the current version at [0][1]. Would be good to hear your thoughts, and if you agree with the approach, I can also port kho_preserve_vmalloc() to work on top of kho_array as well. [0] https://git.kernel.org/pub/scm/linux/kernel/git/pratyush/linux.git/commit/?h=kho-array&id=cf4c04c1e9ac854e3297018ad6dada17c54a59af [1] https://git.kernel.org/pub/scm/linux/kernel/git/pratyush/linux.git/commit/?h=kho-array&id=5eb0d7316274a9c87acaeedd86941979fc4baf96 -- Regards, Pratyush Yadav