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 aGqK7laK /RMBQrb7pXBwt81Is6kXRUL7zqfLWcaCIIF+s3dmKp8nHNkXZdFHKpdgeHBmdKZhS8S54RzcX1F36bNBQjxmt9hhRQ/LEGj6pStpM45w+kccYd8Jn89Lm9gLj+2V85BDUI5SM7gMvLC154smMcKS8LmYp+1URUASs7EEU0v8/yr0t/VsfuerK3QiYT0MKYiDnm2zF7rNUIs/w9aEFl3tIo/yLFj5tAKB/PSNBVFXTsEmRJvbmAs1c8VYmkuQTueYNUYAlD+vSfGizDwwBEohx48Bbq8OWNbfe6BEzyQArYxom/5/oHGEYcUlch757BNLzRbN9wOd0v/WYvVciJRIq9L3vYHhbAbe+sjFy9tAto2d5tHBvL+QcrW4ER59LMrwe23qEbcImi7bBVSGd7Mvo3yZdqtqr/N4UmcmPmdsonol7QChgx2nH5+wNOzNqdvRDjvBxa8tz9InrO06AkQSRsB1ZMA== 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 10 Jun 2025, at 10:03, Lorenzo Stoakes wrote: > On Mon, Jun 09, 2025 at 03:49:52PM -0400, Zi Yan wrote: > [snip] >>> I really think a hard cap, expressed in KB/MB, on pageblock size is the= way to >>> go (but overrideable for people crazy enough to truly want 512 MB pages= - and >>> who cannot then complain about watermarks). >> >> I agree. Basically, I am thinking: >> 1) use something like 2MB as default pageblock size for all arch (the va= lue can >> be set differently if some arch wants a different pageblock size due to = other reasons), this can be done by modifying PAGE_BLOCK_MAX_ORDER=E2=80=99= s default >> value; > > I don't think we can set this using CONFIG_PAGE_BLOCK_MAX_ORDER. > > Because the 'order' will be a different size depending on page size obvio= usly. > > So I'm not sure how this would achieve what we want? > > It seems to me we should have CONFIG_PAGE_BLOCK_MAX_SIZE_MB or something = like > this, and we take min(page_size << CONFIG_PAGE_BLOCK_MAX_ORDER, > CONFIG_PAGE_BLOCK_MAX_SIZE_MB << 20) as the size. OK. Now I get what you mean. Yeah, using MB is clearer as user does not need to know page size to set the right pageblock size. > >> >> 2) make pageblock_order a boot time parameter, so that user who wants >> 512MB pages can still get it by changing pageblock order at boot time. >> > > Again, I don't think order is the right choice here, though having it boo= t time > configurable (perhaps overriding the default config there) seems sensible= . Understood. The new pageblock size should be set using MB. > >> WDYT? > >> >>> >>>> >>>> Often, user just ask for an impossible combination: they >>>> want to use all free memory, because they paid for it, and they >>>> want THPs, because they want max performance. When PMD THP is >>>> small like 2MB, the =E2=80=9Cunusable=E2=80=9D free memory is not that= noticeable, >>>> but when PMD THP is as large as 512MB, user just cannot unsee it. :) >>> >>> Well, users asking for crazy things then being surprised when they get = them >>> is nothing new :P >>> >>>> >>>> >>>> Best Regards, >>>> Yan, Zi >>> >>> Thanks for your input! >>> >>> Cheers, Lorenzo >> >> >> Best Regards, >> Yan, Zi Best Regards, Yan, Zi