On 11/12/21 1:44 AM, Christoph Hellwig wrote: > On Fri, Nov 12, 2021 at 04:37:19PM +0800, Ming Lei wrote: >>> can only be used for reads, and no fua can be set if the preallocating >>> I/O didn't use fua, etc. >>> >>> What are the pitfalls of just chanigng cmd_flags? >> >> Then we need to check cmd_flags carefully, such as hctx->type has to >> be same, flush & passthrough flags has to be same, that said all >> ->cmd_flags used for allocating rqs have to be same with the following >> bio->bi_opf. >> >> In usual cases, I guess all IOs submitted from same plug batch should be >> same type. If not, we can switch to change cmd_flags. > > Jens: is this a limit fitting into your use cases? It's not a big problem for my use case, as that ones all the same type of IO. And in general I don't expect a lot of mixed uses here, I guess the main issue might be a plug for writes and an initial meta data read will "polute" the request cache with requests that we won't be using. But probably not a big enough thing to worry about in terms of efficiency. > I guess as a quick fix this rejecting different flags is probably the > best we can do for now, but I suspect we'll want to eventually relax > them. Agree on both. -- Jens Axboe
