(Sort of) cherry-picked from the out-of-tree drbd9 branch. Original
commit message by Joel Colledge:

    This simplifies drbd_submit_peer_request by removing most of the
    arguments. It also makes the treatment of the op better aligned with
    that in struct bio.

    Determine fault_type dynamically using information which is already
    available instead of passing it in as a parameter.

Note: The opf in receive_rs_deallocated was changed from
REQ_OP_WRITE_ZEROES to REQ_OP_DISCARD. This was required in the
out-of-tree module, and does not matter in-tree. The opf is ignored
anyway in drbd_submit_peer_request, since the discard/zero-out is
decided by the EE_TRIM flag.
Signed-off-by: Joel Colledge <joel.colledge@linbit.com>
Signed-off-by: Christoph Böhmwalder <christoph.boehmwalder@linbit.com>
Link: https://lore.kernel.org/r/20221109133453.51652-4-christoph.boehmwalder@linbit.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

The discard_granularity describes the minimum unit of a discard.
If that is larger than the maximal discard size, we need to disable
discards completely.
Reviewed-by: Joel Colledge <joel.colledge@linbit.com>
Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Christoph Böhmwalder <christoph.boehmwalder@linbit.com>
Link: https://lore.kernel.org/r/20221109133453.51652-3-christoph.boehmwalder@linbit.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

We currently only set q->limits.max_discard_sectors, but that is not
enough. Another field, max_hw_discard_sectors, was introduced in
commit 0034af03 ("block: make /sys/block/<dev>/queue/discard_max_bytes
writeable").

The difference is that max_discard_sectors can be changed from user
space via sysfs, while max_hw_discard_sectors is the "hardware" upper
limit.

So use this helper, which sets both.

This is also a fixup for commit 998e9cbc ("drbd: cleanup
decide_on_discard_support"): if discards are not supported, that does
not necessarily mean we also want to disable write_zeroes.

Fixes: 998e9cbc ("drbd: cleanup decide_on_discard_support")
Reviewed-by: Joel Colledge <joel.colledge@linbit.com>
Signed-off-by: Christoph Böhmwalder <christoph.boehmwalder@linbit.com>
Link: https://lore.kernel.org/r/20221109133453.51652-2-christoph.boehmwalder@linbit.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

Add documentation for the p2pmem/allocate binary file which allows
for allocating p2pmem buffers in userspace for passing to drivers
that support them. (Currently only O_DIRECT to NVMe devices.)
Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Link: https://lore.kernel.org/r/20221021174116.7200-10-logang@deltatee.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

Create a sysfs bin attribute called "allocate" under the existing
"p2pmem" group. The only allowable operation on this file is the mmap()
call.

When mmap() is called on this attribute, the kernel allocates a chunk of
memory from the genalloc and inserts the pages into the VMA. The
dev_pagemap .page_free callback will indicate when these pages are no
longer used and they will be put back into the genalloc.

On device unbind, remove the sysfs file before the memremap_pages are
cleaned up. This ensures unmap_mapping_range() is called on the files
inode and no new mappings can be created.
Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Link: https://lore.kernel.org/r/20221021174116.7200-9-logang@deltatee.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

When a bio's queue supports PCI P2PDMA, set FOLL_PCI_P2PDMA for
iov_iter_get_pages_flags(). This allows PCI P2PDMA pages to be
passed from userspace and enables the NVMe passthru requests to
use P2PDMA pages.
Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Link: https://lore.kernel.org/r/20221021174116.7200-8-logang@deltatee.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

When a bio's queue supports PCI P2PDMA, set FOLL_PCI_P2PDMA for
iov_iter_get_pages_flags(). This allows PCI P2PDMA pages to be passed
from userspace and enables the O_DIRECT path in iomap based filesystems
and direct to block devices.
Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Link: https://lore.kernel.org/r/20221021174116.7200-7-logang@deltatee.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

Consecutive zone device pages should not be merged into the same sgl
or bvec segment with other types of pages or if they belong to different
pgmaps. Otherwise getting the pgmap of a given segment is not possible
without scanning the entire segment. This helper returns true either if
both pages are not zone device pages or both pages are zone device
pages with the same pgmap.

Factor out the check for page mergability into a pages_are_mergable()
helper and add a check with zone_device_pages_are_mergeable().
Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Link: https://lore.kernel.org/r/20221021174116.7200-6-logang@deltatee.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

Consecutive zone device pages should not be merged into the same sgl
or bvec segment with other types of pages or if they belong to different
pgmaps. Otherwise getting the pgmap of a given segment is not possible
without scanning the entire segment. This helper returns true either if
both pages are not zone device pages or both pages are zone device
pages with the same pgmap.

Add a helper to determine if zone device pages are mergeable and use
this helper in page_is_mergeable().
Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Link: https://lore.kernel.org/r/20221021174116.7200-5-logang@deltatee.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

Add iov_iter_get_pages_flags() and iov_iter_get_pages_alloc_flags()
which take a flags argument that is passed to get_user_pages_fast().

This is so that FOLL_PCI_P2PDMA can be passed when appropriate.
Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20221021174116.7200-4-logang@deltatee.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

GUP Callers that expect PCI P2PDMA pages can now set FOLL_PCI_P2PDMA to
allow obtaining P2PDMA pages. If GUP is called without the flag and a
P2PDMA page is found, it will return an error in try_grab_page() or
try_grab_folio().

The check is safe to do before taking the reference to the page in both
cases seeing the page should be protected by either the appropriate
ptl or mmap_lock; or the gup fast guarantees preventing TLB flushes.

try_grab_folio() has one call site that WARNs on failure and cannot
actually deal with the failure of this function (it seems it will
get into an infinite loop). Expand the comment there to document a
couple more conditions on why it will not fail.

FOLL_PCI_P2PDMA cannot be set if FOLL_LONGTERM is set. This is to copy
fsdax until pgmap refcounts are fixed (see the link below for more
information).

Link: https://lkml.kernel.org/r/Yy4Ot5MoOhsgYLTQ@ziepe.caSigned-off-by: Logan Gunthorpe <logang@deltatee.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Link: https://lore.kernel.org/r/20221021174116.7200-3-logang@deltatee.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

In order to add checks for P2PDMA memory into try_grab_page(), expand
the error return from a bool to an int/error code. Update all the
callsites handle change in usage.

Also remove the WARN_ON_ONCE() call at the callsites seeing there
already is a WARN_ON_ONCE() inside the function if it fails.
Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20221021174116.7200-2-logang@deltatee.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

Remove the description of @required_features in elevator_match()
to clear the below warning:

block/elevator.c:103: warning: Excess function parameter 'required_features' description in 'elevator_match'

Link: https://bugzilla.openanolis.cn/show_bug.cgi?id=2734
Fixes: ffb86425 ("block: don't check for required features in elevator_match")
Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Yang Li <yang.lee@linux.alibaba.com>
Link: https://lore.kernel.org/r/20221107062255.2685-1-yang.lee@linux.alibaba.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

if-else is more readable than goto here.
Signed-off-by: Jinlong Chen <nickyc975@zju.edu.cn>
Link: https://lore.kernel.org/r/d3306fa4e92dc9cc614edc8f1802686096bafef2.1667356813.git.nickyc975@zju.edu.cnSigned-off-by: Jens Axboe <axboe@kernel.dk>

Use goto-style error handling like we do elsewhere in the kernel.
Signed-off-by: Jinlong Chen <nickyc975@zju.edu.cn>
Link: https://lore.kernel.org/r/bbbc2d9b17b137798c7fb92042141ca4cbbc58cc.1667356813.git.nickyc975@zju.edu.cnSigned-off-by: Jens Axboe <axboe@kernel.dk>

All controller namespaces share the same tagset, so we can use this
interface which does the optimal operation for parallel quiesce based on
the tagset type(e.g. blocking tagsets and non-blocking tagsets).

nvme connect_q should not be quiesced when quiesce tagset, so set the
QUEUE_FLAG_SKIP_TAGSET_QUIESCE to skip it when init connect_q.

Currently we use NVME_NS_STOPPED to ensure pairing quiescing and
unquiescing. If use blk_mq_[un]quiesce_tagset, NVME_NS_STOPPED will be
invalided, so introduce NVME_CTRL_STOPPED to replace NVME_NS_STOPPED.
In addition, we never really quiesce a single namespace. It is a better
choice to move the flag from ns to ctrl.
Signed-off-by: Chao Leng <lengchao@huawei.com>
[hch: rebased on top of prep patches]
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Keith Busch <kbusch@kernel.org>
Reviewed-by: Chao Leng <lengchao@huawei.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Link: https://lore.kernel.org/r/20221101150050.3510-15-hch@lst.deSigned-off-by: Jens Axboe <axboe@kernel.dk>

Drivers that have shared tagsets may need to quiesce potentially a lot
of request queues that all share a single tagset (e.g. nvme). Add an
interface to quiesce all the queues on a given tagset. This interface is
useful because it can speedup the quiesce by doing it in parallel.

Because some queues should not need to be quiesced (e.g. the nvme
connect_q) when quiescing the tagset, introduce a
QUEUE_FLAG_SKIP_TAGSET_QUIESCE flag to allow this new interface to
ski quiescing a particular queue.
Signed-off-by: Chao Leng <lengchao@huawei.com>
[hch: simplify for the per-tag_set srcu_struct]
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Keith Busch <kbusch@kernel.org>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Chao Leng <lengchao@huawei.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Link: https://lore.kernel.org/r/20221101150050.3510-14-hch@lst.deSigned-off-by: Jens Axboe <axboe@kernel.dk>

Nothing in blk_mq_wait_quiesce_done needs the request_queue now, so just
pass the tagset, and move the non-mq check into the only caller that
needs it.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Keith Busch <kbusch@kernel.org>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Chao Leng <lengchao@huawei.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Link: https://lore.kernel.org/r/20221101150050.3510-13-hch@lst.deSigned-off-by: Jens Axboe <axboe@kernel.dk>

All I/O submissions have fairly similar latencies, and a tagset-wide
quiesce is a fairly common operation.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Keith Busch <kbusch@kernel.org>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Chao Leng <lengchao@huawei.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Link: https://lore.kernel.org/r/20221101150050.3510-12-hch@lst.de
[axboe: fix whitespace]
Signed-off-by: Jens Axboe <axboe@kernel.dk>

For submit_bio based queues there is no (S)RCU critical section during
I/O submission and thus nothing to wait for in blk_mq_wait_quiesce_done,
so skip doing any synchronization.  No non-mq driver should be calling
this, but for now we have core callers that unconditionally call into it.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Keith Busch <kbusch@kernel.org>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Link: https://lore.kernel.org/r/20221101150050.3510-11-hch@lst.deSigned-off-by: Jens Axboe <axboe@kernel.dk>

apple_nvme_reset_work schedules apple_nvme_remove, to be called, which
will call apple_nvme_disable and unquiesce the I/O queues.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Link: https://lore.kernel.org/r/20221101150050.3510-10-hch@lst.deSigned-off-by: Jens Axboe <axboe@kernel.dk>

nvme_remove_dead_ctrl schedules nvme_remove to be called, which will
call nvme_dev_disable and unquiesce the I/O queues.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Link: https://lore.kernel.org/r/20221101150050.3510-9-hch@lst.deSigned-off-by: Jens Axboe <axboe@kernel.dk>

nvme_kill_queues does two things:

 1) mark the gendisk of all namespaces dead
 2) unquiesce all I/O queues

These used to be be intertwined due to block layer issues, but aren't
any more.  So move the unquiscing of the I/O queues into the callers,
and rename the rest of the function to the now more descriptive
nvme_mark_namespaces_dead.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Link: https://lore.kernel.org/r/20221101150050.3510-8-hch@lst.deSigned-off-by: Jens Axboe <axboe@kernel.dk>

None of the callers of nvme_kill_queues needs it to unquiesce the
admin queues, as all of them already do it themselves:

 1) nvme_reset_work explicit call nvme_start_admin_queue toward the
    beginning of the function.  The extra call to nvme_start_admin_queue
    in nvme_reset_work this won't do anything as
    NVME_CTRL_ADMIN_Q_STOPPED will already be cleared.
 2) nvme_remove calls nvme_dev_disable with shutdown flag set to true at
    the very beginning of the function if the PCIe device was not present,
    which is the precondition for the call to nvme_kill_queues.
    nvme_dev_disable already calls nvme_start_admin_queue toward the
    end of the function when the shutdown flag is set to true, so the
    admin queue is already enabled at this point.
 3) nvme_remove_dead_ctrl schedules a workqueue to unbind the driver,
    which will end up in nvme_remove, which calls nvme_dev_disable with
    the shutdown flag.  This case will call nvme_start_admin_queue a bit
    later than before.
 4) apple_nvme_remove uses the same sequence as nvme_remove_dead_ctrl
    above.
 5) nvme_remove_namespaces only calls nvme_kill_queues when the
    controller is in the DEAD state.  That can only happen in the PCIe
    driver, and only from nvme_remove. See item 2) above for the
    conditions there.

So it is safe to just remove the call to nvme_start_admin_queue in
nvme_kill_queues without replacement.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Link: https://lore.kernel.org/r/20221101150050.3510-7-hch@lst.deSigned-off-by: Jens Axboe <axboe@kernel.dk>

At the point where namespaces are marked dead, the controller is in a
non-live state and we won't get pass the identify commands.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Link: https://lore.kernel.org/r/20221101150050.3510-6-hch@lst.deSigned-off-by: Jens Axboe <axboe@kernel.dk>

The NVME_NS_DEAD check only made sense when we revalidated namespaces
in nvme_passthrough_end for commands that affected the namespace inventory.
These days NVME_NS_DEAD is only set during reset or when tearing down
namespaces, and we always remove all namespaces right after that.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Link: https://lore.kernel.org/r/20221101150050.3510-5-hch@lst.deSigned-off-by: Jens Axboe <axboe@kernel.dk>

The call to nvme_remove_invalid_namespaces made sense when
nvme_passthru_end revalidated all namespaces and had to remove those that
didn't exist any more.  Since we don't revalidate from nvme_passthru_end
now, this call is entirely spurious.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Link: https://lore.kernel.org/r/20221101150050.3510-4-hch@lst.deSigned-off-by: Jens Axboe <axboe@kernel.dk>

The code to create, update or delete a tagset and namespaces in
nvme_reset_work is a bit convoluted.  Refactor it with a two high-level
conditionals for first probe vs reset and I/O queues vs no I/O queues
to make the code flow more clear.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Link: https://lore.kernel.org/r/20221101150050.3510-3-hch@lst.de
[axboe: fix whitespace issue]
Signed-off-by: Jens Axboe <axboe@kernel.dk>

nvme and xen-blkfront are already doing this to stop buffered writes from
creating dirty pages that can't be written out later.  Move it to the
common code.

This also removes the comment about the ordering from nvme, as bd_mutex
not only is gone entirely, but also hasn't been used for locking updates
to the disk size long before that, and thus the ordering requirement
documented there doesn't apply any more.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Keith Busch <kbusch@kernel.org>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Chao Leng <lengchao@huawei.com>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Link: https://lore.kernel.org/r/20221101150050.3510-2-hch@lst.deSigned-off-by: Jens Axboe <axboe@kernel.dk>

Prevent unnecessary format conversion for bfqg->bfqd in multiple
places.
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Acked-by: Paolo Valente <paolo.valente@unimore.it>
Link: https://lore.kernel.org/r/20221102022542.3621219-6-yukuai1@huaweicloud.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

Such code are not even compiled since they are inside marco "#if 0".
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Acked-by: Paolo Valente <paolo.valente@unimore.it>
Link: https://lore.kernel.org/r/20221102022542.3621219-5-yukuai1@huaweicloud.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

Just make the code a litter cleaner by removing the unnecessary
variable 'sd'.
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Acked-by: Paolo Valente <paolo.valente@unimore.it>
Link: https://lore.kernel.org/r/20221102022542.3621219-4-yukuai1@huaweicloud.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

Current code is a bit ugly and hard to read.
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Acked-by: Paolo Valente <paolo.valente@unimore.it>
Link: https://lore.kernel.org/r/20221102022542.3621219-3-yukuai1@huaweicloud.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

After the patch "block, bfq: cleanup bfq_weights_tree add/remove apis"),
the local variable 'bfqd' is not used anymore, thus remove it.
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Link: https://lore.kernel.org/r/20221102022542.3621219-2-yukuai1@huaweicloud.com
Fixes: afdba146 ("block, bfq: cleanup bfq_weights_tree add/remove apis")
Signed-off-by: Jens Axboe <axboe@kernel.dk>

We only need a max queue depth for every iolatency to limit the inflight io
number. Replace struct rq_depth with unsigned int to simplfy "struct
iolatency_grp" and save memory.
Signed-off-by: Kemeng Shi <shikemeng@huawei.com>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Link: https://lore.kernel.org/r/20221018111240.22612-4-shikemeng@huawei.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

Default queue depth of iolatency_grp is unlimited, so we scale down
quickly(once by half) in scale_cookie_change. Remove the "subtract
1/16th" part which is not the truth and add the actual way we
scale down.
Signed-off-by: Kemeng Shi <shikemeng@huawei.com>
Link: https://lore.kernel.org/r/20221018111240.22612-3-shikemeng@huawei.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

Function blkcg_iolatency_throttle will make sure blkg->parent is not
NULL before calls check_scale_change. And function check_scale_change
is only called in blkcg_iolatency_throttle.
Signed-off-by: Kemeng Shi <shikemeng@huawei.com>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Link: https://lore.kernel.org/r/20221018111240.22612-2-shikemeng@huawei.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

Split an elevator_disable helper from elevator_switch for the case where
we want to switch to no scheduler at all.  This includes removing the
pointless elevator_switch_mq helper and removing the switch to no
schedule logic from blk_mq_init_sched.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20221030100714.876891-8-hch@lst.deSigned-off-by: Jens Axboe <axboe@kernel.dk>

Checking for the required features in the callers simplifies the code
quite a bit, so do that.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20221030100714.876891-7-hch@lst.de
[axboe: adjust for dropping patch 1, use __elevator_find()]
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Just compare the pointers instead of using the string based
elevator_match.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20221030100714.876891-6-hch@lst.deSigned-off-by: Jens Axboe <axboe@kernel.dk>