blk-cgroup: use group allocation/free of per-cpu counters API

Use group allocation/free of per-cpu counters api to accelerate
blkg_rwstat_init/exit() and simplify code.

Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Link: https://lore.kernel.org/r/20240325035955.50019-1-wangkefeng.wang@huawei.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Revert "blk-cgroup: pin the gendisk in struct blkcg_gq"

This reverts commit 84d7d462b16dd5f0bf7c7ca9254bf81db2c952a2.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20230214183308.1658775-6-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>

blk-cgroup: pin the gendisk in struct blkcg_gq

Currently each blkcg_gq holds a request_queue reference, which is what
is used in the policies. But a lot of these interfaces will move over to
use a gendisk, so store a disk in struct blkcg_gq and hold a reference to
it.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Andreas Herrmann <aherrmann@suse.de>
Acked-by: Tejun Heo <tj@kernel.org>
Link: https://lore.kernel.org/r/20230203150400.3199230-7-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>

blk-cgroup: Fix the recursive blkg rwstat

The current blkio.throttle.io_service_bytes_recursive doesn't
work correctly.

As an example, for the following blkcg hierarchy:
(Made 1GB READ in test1, 512MB READ in test2)
test
/ \
test1 test2

$ head -n 1 test/test1/blkio.throttle.io_service_bytes_recursive
8:0 Read 1073684480
$ head -n 1 test/test2/blkio.throttle.io_service_bytes_recursive
8:0 Read 537448448
$ head -n 1 test/blkio.throttle.io_service_bytes_recursive
8:0 Read 537448448

Clearly, above data of "test" reflects "test2" not "test1"+"test2".

Do the correct summary in blkg_rwstat_recursive_sum().

Signed-off-by: Xunlei Pang <xlpang@linux.alibaba.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

blk-cgroup: separate out blkg_rwstat under CONFIG_BLK_CGROUP_RWSTAT

blkg_rwstat is now only used by bfq-iosched and blk-throtl when on
cgroup1. Let's move it into its own files and gate it behind a config
option.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>