On Tue, Apr 18, 2023 at 03:12:50PM -0400, Johannes Weiner wrote: > pageblock_order can be of various sizes, depending on configuration, > but the default is MAX_ORDER-1. Given 4k pages, that comes out to > 4M. This is a large chunk for the allocator/reclaim/compaction to try > to keep grouped per migratetype. It's also unnecessary as the majority > of higher order allocations - THP and slab - are smaller than that. > > Before subsequent patches increase the effort that goes into > maintaining migratetype isolation, it's important to first set the > defrag block size to what's likely to have common consumers. > > Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx> This patch may be a distraction in the context of this series. I don't feel particularly strongly about it but it has strong bikeshed potential. For configurations that support huge pages of any sort, it should be PMD_ORDER, for anything else the choice is arbitrary. 2M is as good a guess as anyway because even if it was tied to the PAGE_ALLOC_COSTLY_ORDER then the pageblock bitmap overhead might be annoying. -- Mel Gorman SUSE Labs
