On Mon, Aug 18, 2025 at 02:31:20PM +0800, Yu Kuai wrote: > Hi, > > 在 2025/08/18 14:18, Christoph Hellwig 写道: > > On Mon, Aug 18, 2025 at 02:14:06PM +0800, Yu Kuai wrote: > > > Please take a look at the first patch, nothing special, the new flag > > > will be passed to the top device. > > > > But passing it on will be incorrect in many cases, e.g. for any > > write caching solution. And that is a much more common use case > > than stacking different raid level using block layer stacking. > > I don't quite understand why it's incorrect for write caching solution, > can you please explain in details? AFAIK, the behaviour is only changed > for the first mdraid device is the stacking chain. The way I read the patch, the flag is inherited if any underlying device sets it. Now if you stack something that buffers most I/O the md raid limits aren't really that relevant, and you'd rather expose the limits for the writeback or read caching.
