On Wed, Dec 8, 2021 at 10:38 PM Christoph Hellwig <hch@xxxxxx> wrote: > > While using the MC-safe copy routines is rather pointless on a virtual device > like virtiofs, it also isn't harmful at all. So just use _copy_mc_to_iter > unconditionally to simplify the code. >From a correctness perspective, yes, but from a performance perspective, see: enable_copy_mc_fragile() ...on those platforms fast-string copy implementation is replaced with a manual unrolled copy. So this will cause a performance regression on those platforms. How about let's keep this as is / still only use it for PMEM where end users are already dealing with the performance difference across platforms? I considered exporting an indicator of which backend routine has been selected from arch/x86/lib/copy_mc.c, but it got messy quickly so I fell back to just keeping the status quo.
