On 17/07/2024 11:03, David Hildenbrand wrote: >>>>>> >>>>>> But today, controls and stats are exposed for: >>>>>> >>>>>> anon: >>>>>> min order: 2 >>>>>> max order: PMD_ORDER >>>>>> anon-shmem: >>>>>> min order: 2 >>>>>> max order: PMD_ORDER >>>>>> tmpfs-shmem: >>>>>> min order: PMD_ORDER >>>>>> max order: PMD_ORDER >>>>>> file: >>>>>> min order: Nothing yet (this patch proposes 1) >>>>>> max order: Nothing yet (this patch proposes MAX_PAGECACHE_ORDER) >>>>>> >>>>>> So I think there is definitely a bug for shmem where the minimum order >>>>>> control >>>>>> should be order-1 but its currently order-2. >>>>> >>>>> Maybe, did not play with that yet. Likely order-1 will work. (although >>>>> probably >>>>> of questionable use :) ) >>>> >>>> You might have to expand on why its of "questionable use". I'd assume it has >>>> the >>>> same amount of value as using order-1 for regular page cache pages? i.e. half >>>> the number of objects to manage for the same amount of memory. >>> >>> order-1 was recently added for the pagecache to get some device setups running >>> (IIRC, where we cannot use order-0, because device blocksize > PAGE_SIZE). >>> >>> You might be right about "half the number of objects", but likely just going for >>> order-2, order-3, order-4 ... for shmem might be even better. And simply falling >>> back to order-0 when you cannot get the larger orders. >> >> Sure, but then you're into the territory of baking in policy. Remember that >> originally I was only interested in 64K but the concensus was to expose all the >> sizes. Same argument applies to 8K; expose it and let others decide policy. > > I don't disagree. The point I'm trying to make is that there was so far there > was no strong evidence that it is really required. Support for the pagecache had > a different motivation for these special devices. Sure, but there was no clear need for anon mTHP orders other than order-2 and order-4 (for arm64's HPA and contpte, respectively), but we still chose to expose all the others. > > But again, I agree that we should just make it consistent and allow for it. :) Yes, we both agree, so I'll stop arguing now :) Thanks, as always, for the discussion!
