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Thu, 28 Aug 2025 16:00:29 -0700 (PDT) MIME-Version: 1.0 References: <20250807014442.3829950-1-pasha.tatashin@soleen.com> <20250807014442.3829950-30-pasha.tatashin@soleen.com> <20250826162019.GD2130239@nvidia.com> <20250828124320.GB7333@nvidia.com> In-Reply-To: <20250828124320.GB7333@nvidia.com> From: Chris Li Date: Thu, 28 Aug 2025 16:00:18 -0700 X-Gmail-Original-Message-ID: X-Gm-Features: Ac12FXwgAj48kKV8-NSqN51LxVJutv6tGbA-WA_eygERRbP7T7KY6y3bnmWLRPM Message-ID: Subject: Re: [PATCH v3 29/30] luo: allow preserving memfd To: Jason Gunthorpe Cc: Pratyush Yadav , Pasha Tatashin , jasonmiu@google.com, graf@amazon.com, changyuanl@google.com, rppt@kernel.org, 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 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Stat-Signature: utuhesxgcck6z89e6bsyx1rner4zmoct X-Rspam-User: X-Rspamd-Queue-Id: 742C3100014 X-Rspamd-Server: rspam05 X-HE-Tag: 1756422032-298322 X-HE-Meta: U2FsdGVkX19OUaljw+Y3U4Ec9SXUYxMsPlOLlDmbRiTo81Zbwn33hena/kM2t2/fB0ZqilEbDnJs9+QXKsKbP/P4AxM5YTFrOwaKkHdkqfgawcm53lR5TF43SqHqBCFf3byNBk/g47uvDGd6tR+lDvHY2jOX/BtwV6nbr8gWCs7GM3rXr3jalPcbbo04L+mSAXEirybsnR82jDqsvO01Z3H9geqlMfVc6EA7V2cd16qoMbxxL713NmSAzHQ0M3+KkTB0V4sgMYNaOlA/yu7rIuTCT4ku2jSWdq3cJ1xEORbZC70elscr2K4Iifx0g1PDCkzyix27Sy+fsE7l81uyeE/KxW7PEQM7byij0IkUw3nr8x92qWeq0a2Q456tlNUabmUdlY/0KOUkzCarPsat0C9JQWwxkmm14mJ4yP1h6yT2IDsXu9HxJudMWmHgEhpwFTOq/NWg+dmUvVdeaTIgOpkqoeEcZ73B5vTQSuhRarVJNEKujQ/l8vltvWhsRlVb31poAIjYc99oMfiPx52Ap+gpHCkN7/RzN+IC1kkDBT538hFcbMehqHEiQgGM7Rgix54+T/5L5k2rKy0VaRV1kM473seopr2Kk65JpJJ/9LtzPC/EKjVFF8VX7BHhNl40OqN9lP6JWqm/JLG99f9lgf1tMtDs1wR6ta9kiLD8FbARfHdV4PheWQgKgi+HpkGljS5HUxzGkIt7fSY9SmB7LFTnf8qY31mAajRpCA0TgTojEkTOgj2c00VO4boAmxvzB8I7zfT6TDI7lTV8ccFSvCpcxGTSobWCuwJw7ngzG6Q8NX6gUH0Kl8N+TMdxPwGBox6P3NiQs40YhuS041xalkF9Vg6qPohpSKB5EHzcPNAS7mvazgqh1Mti5RyQLcSRL7kEzSUe9kyZm6Ib0ISG7ReLpAYl1D9/WDhGfAXfBDwI7dKyVKTS8/X1u1kZfAN1cbv/eGfEiy3pgROpgbl UyinCX1I mjB/HlaMbnl1pzQlMufgl1hYfXJRhsze9BYp76gydiXzmdmzR1M+8RfTtR1YIs6dOP5RT/j7oM1Me+R208JFN0K1ITCCdYrGtJHOEq9FtDQmoHXvbWx7/LR0b5/340sZ2uAjjPuKcIYAtvnHZAKEjdekGETFCaQ0f4u5k2nDL6KjRWkZxP5E2HMNByyxmWe668qrB2fhPUg4iXsNDI6+FSZFwBALYD258ylJ9/oPfPtEWaeGA54B0xTBR2+cgE6wVNt7NvIHNI0/m0F1+E5RX6MCu8LBfQONLRulwah76wA34za3RV0CECPvcIHmLJ6EFSofMCyWB4RkGxvJxlcTGTRdHrS9N61llwuCwPelUmNMBlMFJSsGNfNJ4Hg== 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 Thu, Aug 28, 2025 at 5:43=E2=80=AFAM Jason Gunthorpe wr= ote: > > On Wed, Aug 27, 2025 at 05:03:55PM +0200, Pratyush Yadav wrote: > > > I think we need something a luo_xarray data structure that users like > > memfd (and later hugetlb and guest_memfd and maybe others) can build to > > make serialization easier. It will cover both contiguous arrays and > > arrays with some holes in them. > > I'm not sure xarray is the right way to go, it is very complex data > structure and building a kho variation of it seems like it is a huge > amount of work. > > I'd stick with simple kvalloc type approaches until we really run into > trouble. > > You can always map a sparse xarray into a kvalloc linear list by > including the xarray index in each entry. Each entry will be 16 byte, 8 for index and 8 for XAvalue, right? > Especially for memfd where we don't actually expect any sparsity in > real uses cases there is no reason to invest a huge effort to optimize > for it.. Ack. > > > As I explained above, the versioning is already there. Beyond that, why > > do you think a raw C struct is better than FDT? It is just another way > > of expressing the same information. FDT is a bit more cumbersome to > > write and read, but comes at the benefit of more introspect-ability. > > Doesn't have the size limitations, is easier to work list, runs > faster. Yes, especially when you have a large array. Chris