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[2003:cb:c71e:600:9fbb:f0bf:d958:5c70]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-430d70b4331sm165472335e9.36.2024.10.14.13.32.36 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 14 Oct 2024 13:32:38 -0700 (PDT) Message-ID: <01fbdcef-b923-4bb0-80b0-f1d3e57fe515@redhat.com> Date: Mon, 14 Oct 2024 22:32:36 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/3] memory: extern memory_block_size_bytes and set_memory_block_size_order To: Gregory Price Cc: linux-cxl@vger.kernel.org, x86@kernel.org, linux-mm@kvack.org, linux-acpi@vger.kernel.org, linux-kernel@vger.kernel.org, dave.hansen@linux.intel.com, luto@kernel.org, peterz@infradead.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, hpa@zytor.com, osalvador@suse.de, gregkh@linuxfoundation.org, rafael@kernel.org, akpm@linux-foundation.org, dan.j.williams@intel.com, Jonathan.Cameron@huawei.com, alison.schofield@intel.com, rrichter@amd.com, terry.bowman@amd.com, lenb@kernel.org, dave.jiang@intel.com, ira.weiny@intel.com References: <20241008044355.4325-1-gourry@gourry.net> <20241008044355.4325-2-gourry@gourry.net> <039e8c87-c5da-4469-b10e-e57dd5662cff@redhat.com> <2c854e5e-c200-4ed9-bf21-778779af7e5b@redhat.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 8B5CE80007 X-Stat-Signature: yncemdaxm8uwdgd5ozijrzxrkyemjmhn X-HE-Tag: 1728937950-777940 X-HE-Meta: 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 waNCXfrr FZQUehrERhFJtOPMx/QKeW0F3XOLpDE5waIW5GvKJYnEJ60cPhWAjqYjkEI6oO05OoJg3Qm6z2E23E8dg9XZSNDHsbPaVCBa1icMGEfeRIseC/CFOl7C9d0HV9FbtuJUXkefnBd3xYKCnoa2hqsfnpHqrhg4rTdbAugkcaXw5/M0WfVUwUbRlsN0zblh9pZSH3tC5sZCNkDvIh8YoA6vDU+31oAEH8wS3g0WuE45OpClVAlaxTrqNOYtt7UvZdwHZa3c+b3GwuSQ8yXBGBtl/zM3M2ly/UETdLWm+laREXX5ZAZ5l6DL4ajfEazzczLhzPD3Li4Jer8Ln1c0mbD6erWq23MoDossY7xH0HtphWY9GhNye9D43ON+Zn0pv+4tfj0PUdnCUt7QyVKwFbFaXoNOAc+B6HLEYiSSvLfiupHWOMCSQgf7DMMq147aX91YAzpKD 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 14.10.24 16:25, Gregory Price wrote: > On Mon, Oct 14, 2024 at 01:54:27PM +0200, David Hildenbrand wrote: >> On 08.10.24 17:21, Gregory Price wrote: >>> On Tue, Oct 08, 2024 at 05:02:33PM +0200, David Hildenbrand wrote: >>>> On 08.10.24 16:51, Gregory Price wrote: >>>>>>> +int __weak set_memory_block_size_order(unsigned int order) >>>>>>> +{ >>>>>>> + return -ENODEV; >>>>>>> +} >>>>>>> +EXPORT_SYMBOL_GPL(set_memory_block_size_order); >>>>>> >>>>>> I can understand what you are trying to achieve, but letting arbitrary >>>>>> modules mess with this sounds like a bad idea. >>>>>> >>>>> >>>>> I suppose the alternative is trying to scan the CEDT from inside each >>>>> machine, rather than the ACPI driver? Seems less maintainable. >>>>> >>>>> I don't entirely disagree with your comment. I hummed and hawwed over >>>>> externing this - hence the warning in the x86 machine. >>>>> >>>>> Open to better answers. >>>> >>>> Maybe an interface to add more restrictions on the maximum size might be >>>> better (instead of setting the size/order, you would impose another upper >>>> limit). >>> >>> That is effectively what set_memory_block_size_order is, though. Once >>> blocks are exposed to the allocators, its no longer safe to change the >>> size (in part because it was built assuming it wouldn't change, but I >>> imagine there are other dragons waiting in the shadows to bite me). >> >> Yes, we must run very early. >> >> How is this supposed to interact with code like >> >> set_block_size() >> >> that also calls set_memory_block_size_order() on UV systems (assuming there >> will be CXL support sooner or later?)? >> >> > > Tying the other email to this one - just clarifying the way forward here. > > It sounds like you're saying at a minimum drop EXPORT tags to prevent > modules from calling it - but it also sounds like built-ins need to be > prevented from touching it as well after a certain point in early boot. Right, at least the EXPORT is not required. > > Do you think I should go down the advise() path as suggested by Ira, > just adding a arch_lock_blocksize() bit and have set_..._order check it, > or should we just move towards each architecture having to go through > the ACPI:CEDT itself? Let's summarize what we currently have on x86 is: 1) probe_memory_block_size() Triggered on first memory_block_size_bytes() invocation. Makes a decision based on: a) Already set size using set_memory_block_size_order() b) RAM size c) Bare metal vs. virt (bare metal -> use max) d) Virt: largest block size aligned to memory end 2) set_memory_block_size_order() Triggered by set_block_size() on UV systems. I don't think set_memory_block_size_order() is the right tool to use. We just want to leave that alone I think -- it's a direct translation of a kernel cmdline parameter that should win. You essentially want to tweak the b)->d) logic to take other alignment into consideration. Maybe have some simple callback mechanism probe_memory_block_size() that can consult other sources for alignment requirements? If that's not an option, then another way to set further min-alignment requirements (whereby we take MIN(old_align, new_align))? -- Cheers, David / dhildenb