On Thu, Oct 12, 2023 at 11:19:08AM -0700, Darrick J. Wong wrote: > On Thu, Oct 12, 2023 at 07:25:11AM +0200, Christoph Hellwig wrote: > > On Wed, Oct 11, 2023 at 11:06:14AM -0700, Darrick J. Wong wrote: > > > From: Darrick J. Wong <djwong@xxxxxxxxxx> > > > > > > Avoid the costs of integer division (32-bit and 64-bit) if the realtime > > > extent size is a power of two. > > > > Looks good: > > > > Reviewed-by: Christoph Hellwig <hch@xxxxxx> > > > > Do you have any data on how common non-power of two rtext sizes are? > > Might it be worth to add unlikely annotations? > > I don't really know about the historical uses. There might be old > filesystems out there with a non-power-of-2 raid stripe size that are > set up for full stripe allocations for speed. > > We (oracle) are interested in using rt for PMD allocations on pmem/cxl > devices and atomic writes on scsi/nvme devices. Both of those cases > will only ever use powers of 2. > > I'll add some if-test annotations and we'll see if anyone notices. ;) > > --D We are using 1044KB realtime extents (blocksize = 4096, rextsize = 261) for our blob storage system. It's a goofy number, but IIRC it was chosen because their most common blob sizes were single-digit multiples of a megabyte, and they wanted a large-ish (~1MB) realtime extent size to reduce external fragmentation, but they also wanted to store a bit of extra metadata without requiring an extra realtime extent and blowing up internal fragmentation.
