On 10/5/21 4:23 AM, John Garry wrote:

Currently a full set of static requests are allocated per hw queue per
tagset when shared sbitmap is used.

However, only tagset->queue_depth number of requests may be active at
any given time. As such, only tagset->queue_depth number of static
requests are required.

The same goes for using an IO scheduler, which allocates a full set of
static requests per hw queue per request queue.

This series changes shared sbitmap support by using a shared tags per
tagset and request queue. Ming suggested something along those lines in
v1 review. In using a shared tags, the static rqs also become shared,
reducing the number of sets of static rqs, reducing memory usage.

Patch "blk-mq: Use shared tags for shared sbitmap support" is a bit big,
and could potentially be broken down. But then maintaining ability to
bisect becomes harder and each sub-patch would get more convoluted.

For megaraid sas driver on my 128-CPU arm64 system with 1x SATA disk, we
save approx. 300MB(!) [370MB -> 60MB]

Baseline is 1b2d1439fc25 (block/for-next) Merge branch 'for-5.16/io_uring'
into for-next

Let's get this queued up for testing, thanks John.

-- 
Jens Axboe