On 14/04/2023 17:18, Matthew Wilcox wrote: > On Fri, Apr 14, 2023 at 05:06:49PM +0100, Ryan Roberts wrote: >> The point I'm thinking about is for 4K pages, we need to allocate 64K blocks to >> use the contig bit. Roughly I guess that means going from average of 2K wastage >> per anon VMA to 32K. Perhaps you can get away with that for a decent perf uplift. >> >> But for 64K pages, we need to allocate 2M blocks to use the contig bit. So that >> takes average wastage from 32K to 1M. That feels a bit harder to justify. >> Perhaps here, we should make a decision based on MADV_HUGEPAGE? >> >> So perhaps we actually want 2 values: one for if MADV_HUGEPAGE is not set on the >> VMA, and one if it is? (with 64K pages I'm guessing there are many cases where >> we won't PMD-map THPs - its 512MB). > > I'm kind of hoping that all this work takes away the benefit from > CONFIG_PAGE_SIZE_64K, and we can just use 4k pages everywhere. That sounds great. I'm not sure I share your confidence though ;-)
