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b=T9dmzbN3vJLJmQDq1Re5bzl8OxpzTbtxHyo9VrZ09/exjPs4/S/UQ/qjokktB5xH0 SSAhxDYKrSqviNam9PJfJyWLgwI4zqdg3I1711MwPV/OjBcVgO1pnXEGeXz3WuK0Xv UVuAAVWCHK9DEEZHqKg20aHU8P+mQKhAhInpwws4Klng0iRivbKWCQXm3KK6C52Kus igQubipBz8w3WOXaDSc+DURspm2666u/anhAH4CayF+VNK79UQd6Dcbo23j5PKLmkc 7e7Mzu21+so4+IDhVLL5kTXhZiCBHk37Mq4vGWxsegGW2R/VeQMTHWMDaNdZO+jGo4 NR5zsktrqL/VA== From: Pratyush Yadav To: Pasha Tatashin Cc: Mike Rapoport , Jason Gunthorpe , 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 19:21:31 +0200 Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Stat-Signature: qguqdudsr1i1twdi6odgwff4w4nq1ccd X-Rspam-User: X-Rspamd-Queue-Id: 88417A000E X-Rspamd-Server: rspam05 X-HE-Tag: 1756747304-770424 X-HE-Meta: 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 ziLYyShv fjQNZIicVI2EftBNjCCuZV1KlWE31a0YFfLuyKAlkrAUFkXWw8l/qzjoQfxPY8cw6k/cpPYh8TCkiYQqOrsMz7KSdesFzzLwPZl+Vu7rlZB5Dq0F0cmNgzJjeg5De4K1YjOmUxqAIwBfBpMASzxn1M65WhvmvfMSUX3DByRsZoOIFIyHhQucOh103RyAzpK1gX00udROWCvXLlW/zAGZRvhv4BhI3WEv2jkg84kDmR7/vKbEBo4hvgOA6r12IZFL+1MUdFgBD3zVq4ReMqXlBDZGnY+JzW5Osa5btID4yrLUbsJ3y6nEMjD6dhg== 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 Pasha, On Mon, Sep 01 2025, Pasha Tatashin wrote: > On Mon, Sep 1, 2025 at 4:23=E2=80=AFPM Mike Rapoport wr= ote: >> >> 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 tak= e its >> > > + * size, plus a page for other properties. >> > > + */ >> > > + fdt =3D memfd_luo_create_fdt(PAGE_ALIGN(preserved_size) + PAGE_S= IZE); >> > > + if (!fdt) { >> > > + err =3D -ENOMEM; >> > > + goto err_unpin; >> > > + } >> > >> > This doesn't seem to have any versioning scheme, it really should.. >> > >> > > + err =3D 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 =3D -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=3D= kho/vmalloc/v1 > > The patch looks okay to me, but it doesn't support holes in vmap > areas. While that is likely acceptable for vmalloc, it could be a > problem if we want to preserve memfd with holes and using vmap > preservation as a method, which would require a different approach. > Still, this would help with preserving memfd. I agree. I think we should do it the other way round. Build a sparse array first, and then use that to build vmap preservation. Our emails seem to have crossed, but see my reply to Mike [0] that describes my idea a bit more, along with WIP code. [0] https://lore.kernel.org/lkml/mafs0ldmyw1hp.fsf@kernel.org/ > > However, I wonder if we should add a separate preservation library on > top of the kho and not as part of kho (or at least keep them in a > separate file from core logic). This would allow us to preserve more > advanced data structures such as this and define preservation version > control, similar to Jason's store_object/restore_object proposal. This is how I have done it in my code: created a separate file called kho_array.c. If we have enough such data structures, we can probably move it under kernel/liveupdate/lib/. As for the store_object/restore_object proposal: see an alternate idea at [1]. [1] https://lore.kernel.org/lkml/mafs0h5xmw12a.fsf@kernel.org/ --=20 Regards, Pratyush Yadav