> On Aug 30, 2021, at 12:28 PM, Darrick J. Wong <djwong@xxxxxxxxxx> wrote: > > On Sat, Aug 28, 2021 at 01:27:29PM -0600, Andreas Dilger wrote: >> On Aug 28, 2021, at 1:04 PM, Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote: >>> >>> The current folio work is focused on permitting the VM to use >>> physically contiguous chunks of memory. Both Darrick and Johannes >>> have pointed out the advantages of supporting logically-contiguous, >>> physically-discontiguous chunks of memory. Johannes wants to be able to >>> use order-0 allocations to allocate larger folios, getting the benefit >>> of managing the memory in larger chunks without requiring the memory >>> allocator to be able to find contiguous chunks. Darrick wants to support >>> non-power-of-two block sizes. >> >> What is the use case for non-power-of-two block sizes? The main question >> is whether that use case is important enough to add the complexity and >> overhead in order to support it? > > For copy-on-write to a XFS realtime volume where the allocation extent > size (we support bigalloc too! :P) is not a power of two (e.g. you set > up a 4 disk raid5 with 64k stripes, now the extent size is 192k). > > Granted, I don't think folios handling 192k chunks is absolutely > *required* for folios; the only hard requirement is that if any page in > a 192k extent becomes dirty, the rest have to get written out all the > same time, and the cow remap can only happen after the last page > finishes writeback. OK, they are still multiples of PAGE_SIZE. That wasn't clear, I thought these were byte-granular IOs or something... Cheers, Andreas
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