On Sat, Jan 04, 2025 at 04:59:39PM -0800, Keith Busch wrote: > On Fri, Jan 03, 2025 at 08:04:32PM -0800, Luis Chamberlain wrote: > > On Fri, Jan 03, 2025 at 06:15:55PM -0800, Bart Van Assche wrote: > > > On 1/3/25 5:47 PM, Luis Chamberlain wrote: > > > > While that addresses a smaller segment then page size this still leaves > > > > open the question of if a dma segment can be larger than page size, > > > Hmm ... aren't max_segment_size values that are larger than the page > > > size supported since day one of the Linux kernel? Or are you perhaps > > > referring to Ming's multi-page bvec patch series that was merged about > > > six years ago? > > > > Try aiming high for a single 2 MiB for a single IO on x86_64 on NVMe, that is > > currently not possible. At the max 128 NVMe number of DMA segments, and we have > > 4 KiB per DMA segment, for a 512 KiB IO limit. Should multi-page bvec > > enable to lift this? > > You need huge pages to guarantee you can reach those transfer sizes in a > single command. Otherwise you need to get lucky with larger contiguous > folios, which can certainly happen but it's just not as desterministic. Now with min-order support, it is deterministic. Luis
