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. --D > Cheers, Andreas > > > > >
