On Thu, May 29, 2025 at 04:44:51PM +0530, Kundan Kumar wrote: > Number of writeback contexts > =========================== > The plan is to keep the nr_wb_ctx as 1, ensuring default single threaded > behavior. However, we set the number of writeback contexts equal to > number of CPUs in the current version. Later we will make it configurable > using a mount option, allowing filesystems to choose the optimal number > of writeback contexts. Well, the proper thing would be to figure out a good default and not just keep things as-is, no? > IOPS and throughput > =================== > We see significant improvement in IOPS across several filesystem on both > PMEM and NVMe devices. > > Performance gains: > - On PMEM: > Base XFS : 544 MiB/s > Parallel Writeback XFS : 1015 MiB/s (+86%) > Base EXT4 : 536 MiB/s > Parallel Writeback EXT4 : 1047 MiB/s (+95%) > > - On NVMe: > Base XFS : 651 MiB/s > Parallel Writeback XFS : 808 MiB/s (+24%) > Base EXT4 : 494 MiB/s > Parallel Writeback EXT4 : 797 MiB/s (+61%) What worksload was this? How many CPU cores did the system have, how many AGs/BGs did the file systems have? What SSD/Pmem was this? Did this change the write amp as measure by the media writes on the NVMe SSD? Also I'd be really curious to see numbers on hard drives. > We also see that there is no increase in filesystem fragmentation > # of extents: > - On XFS (on PMEM): > Base XFS : 1964 > Parallel Writeback XFS : 1384 > > - On EXT4 (on PMEM): > Base EXT4 : 21 > Parallel Writeback EXT4 : 11 How were the number of extents counts given that they look so wildly different?
