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b=GKpbgHVAB96CTF2QAU6gGXB9xyAtOYn7EP9js0Mycon0OeXhF2jqHHtX89c5XmG3n aI+GsuLi5aWWIqQuOeufUD4aA/2oqU4CL3hOKgWLJISLTlCDKD2fvEzTYvo+4axv1Y RMC80Z36Upuv7S76Aj7akkAJYpehDBHHl02KtLD9+owbFDV5HjZtX2uU4oNhmImcTZ TB6NozxahkQlkcbHdVJIiuprn3ewx0G92tYj/3ivDFDMjJkdV5nEmpt/dhUVJduyaG M6PpSxx1REjCjMlgwB+uTMHEl+k2ror8Zzap/3OLPhR5zcZpm4wrMVCWSYXfzyE61t +lyMXl3tACR7w== From: Pratyush Yadav To: Pasha Tatashin Cc: pratyush@kernel.org, jasonmiu@google.com, graf@amazon.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, jgg@nvidia.com, parav@nvidia.com, leonro@nvidia.com, witu@nvidia.com, hughd@google.com, skhawaja@google.com, chrisl@kernel.org Subject: Re: [PATCH v5 18/22] docs: add documentation for memfd preservation via LUO In-Reply-To: (Pasha Tatashin's message of "Thu, 13 Nov 2025 11:55:25 -0500") References: <20251107210526.257742-1-pasha.tatashin@soleen.com> <20251107210526.257742-19-pasha.tatashin@soleen.com> Date: Thu, 13 Nov 2025 17:59:51 +0100 Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 Content-Type: text/plain X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: A1AE61C000C X-Stat-Signature: ce78cnd7hx1ndt673oqwu6qemy4k6x5x X-Rspam-User: X-HE-Tag: 1763053203-283707 X-HE-Meta: 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 into0hhB JsWD3t+aOmTx4fvHPITXsOPrcOwzp15shZEmJuzKwCNKMSjAHa8OjGL11xpbZ8mFwl+WX0wNbDchI33mAyaVxmVmLYC6UFjk9VplAUh+g2Y32lh6BggFd0SJcR9L34BWXhhw5gces/k/Qq5K8Wd0YfQ4Ch3avO0bpb4cZO7pd0MOomPHHNdaFwWAlDtvDDHQT/B+D/PddEzVH4ZZNCbFuAH2WYPkvPXCmLEuaAEkoIXC/rdY= 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, Nov 13 2025, Pasha Tatashin wrote: >> +Limitations >> +=========== >> + >> +The current implementation has the following limitations: >> + >> +Size >> + Currently the size of the file is limited by the size of the FDT. The FDT can >> + be at of most ``MAX_PAGE_ORDER`` order. By default this is 4 MiB with 4K >> + pages. Each page in the file is tracked using 16 bytes. This limits the >> + maximum size of the file to 1 GiB. > > The above should be removed, as we are using KHO vmalloc that resolves > this limitation. Pratyush, I suggest for v6 let's move memfd > documnetation right into the code: memfd_luo.c and > liveupdate/abi/memfd.h, and source it from there. ACK. I think the section on behavior in different phases is also out of date now, and the serialization format too. The format is more accurately defined in include/linux/liveupdate/abi/memfd.h. So this documentation needs an overhaul. I don't mind moving it to the code and including it in the HTML docs via kernel-doc. Will do that for the next revision. > > Keeping documentation with the code helps reduce code/doc divergence. > > Pasha -- Regards, Pratyush Yadav