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 value 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’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 obviously. 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. > > 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 boot time configurable (perhaps overriding the default config there) seems sensible. > 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 “unusable” 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
