On 27/04/2021 10:52, Ming Lei wrote:

quoted

quoted

Then you just waste lots of memory, I remember that scsi request payload
is a bit big.

It's true that we waste much memory for regular static requests for when
using hostwide tags today.

One problem in trying to use a single set of "hostwide" static requests is
that we call blk_mq_init_request(..., hctx_idx, ...) ->
set->ops->init_request(.., hctx_idx, ...) for each static rq, and this would
not work for a single set of "hostwide" requests.

And I see a similar problem for a "request queue-wide" sched static
requests.

Maybe we can improve this in future.

OK, fair enough.

JFYI, I am working on this now.

My idea is to introduce a hostwide and request-wide static requests (for 
hostwide tagset), and have the per-hctx tags point at them, so that we 
don't need to allocate per-hctx static requests.

SCSI init_request callback just ignores hctx_idx passed, so then we can 
just call init_request(hctx_idx = 0) for those hostwide/request 
queue-wide static requests.

Thanks,
John