Switch to the naming used by the other entries so that we can use the
QUEUE_RW_ENTRY helper.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Add two helpers macros to avoid boilerplate code for the queue sysfs
entries.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NJohannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

The sparse tool complains as follows:

kernel/trace/blktrace.c:796:5: warning:
 symbol 'blk_trace_bio_get_cgid' was not declared. Should it be static?

This function is not used outside of blktrace.c, so this commit
marks it static.
Reported-by: NHulk Robot <hulkci@huawei.com>
Signed-off-by: NWang Hai <wanghai38@huawei.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Now we usually free the hctx->sched_data by e->type->ops.exit_hctx(),
and no users will use blk_mq_sched_free_hctx_data() function.
Remove it.
Signed-off-by: NBaolin Wang <baolin.wang@linux.alibaba.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Discarding blocks and buffers under a mounted filesystem is hardly
anything admin wants to do. Usually it will confuse the filesystem and
sometimes the loss of buffer_head state (including b_private field) can
even cause crashes like:

BUG: unable to handle kernel NULL pointer dereference at 0000000000000008
PGD 0 P4D 0
Oops: 0002 [#1] SMP PTI
CPU: 4 PID: 203778 Comm: jbd2/dm-3-8 Kdump: loaded Tainted: G O     --------- -  - 4.18.0-147.5.0.5.h126.eulerosv2r9.x86_64 #1
Hardware name: Huawei RH2288H V3/BC11HGSA0, BIOS 1.57 08/11/2015
RIP: 0010:jbd2_journal_grab_journal_head+0x1b/0x40 [jbd2]
...
Call Trace:
 __jbd2_journal_insert_checkpoint+0x23/0x70 [jbd2]
 jbd2_journal_commit_transaction+0x155f/0x1b60 [jbd2]
 kjournald2+0xbd/0x270 [jbd2]

So if we don't have block device open with O_EXCL already, claim the
block device while we truncate buffer cache. This makes sure any
exclusive block device user (such as filesystem) cannot operate on the
device while we are discarding buffer cache.
Reported-by: NYe Bin <yebin10@huawei.com>
Signed-off-by: NJan Kara <jack@suse.cz>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
[axboe: fix !CONFIG_BLOCK error in truncate_bdev_range()]
Signed-off-by: NJens Axboe <axboe@kernel.dk>

If block_write_full_page() is called for a page that is beyond current
inode size, it will truncate page buffers for the page and return 0.
This logic has been added in 2.5.62 in commit 81eb69062588 ("fix ext3
BUG due to race with truncate") in history.git tree to fix a problem
with ext3 in data=ordered mode. This particular problem doesn't exist
anymore because ext3 is long gone and ext4 handles ordered data
differently. Also normally buffers are invalidated by truncate code and
there's no need to specially handle this in ->writepage() code.

This invalidation of page buffers in block_write_full_page() is causing
issues to filesystems (e.g. ext4 or ocfs2) when block device is shrunk
under filesystem's hands and metadata buffers get discarded while being
tracked by the journalling layer. Although it is obviously "not
supported" it can cause kernel crashes like:

[ 7986.689400] BUG: unable to handle kernel NULL pointer dereference at
+0000000000000008
[ 7986.697197] PGD 0 P4D 0
[ 7986.699724] Oops: 0002 [#1] SMP PTI
[ 7986.703200] CPU: 4 PID: 203778 Comm: jbd2/dm-3-8 Kdump: loaded Tainted: G
+O     --------- -  - 4.18.0-147.5.0.5.h126.eulerosv2r9.x86_64 #1
[ 7986.716438] Hardware name: Huawei RH2288H V3/BC11HGSA0, BIOS 1.57 08/11/2015
[ 7986.723462] RIP: 0010:jbd2_journal_grab_journal_head+0x1b/0x40 [jbd2]
...
[ 7986.810150] Call Trace:
[ 7986.812595]  __jbd2_journal_insert_checkpoint+0x23/0x70 [jbd2]
[ 7986.818408]  jbd2_journal_commit_transaction+0x155f/0x1b60 [jbd2]
[ 7986.836467]  kjournald2+0xbd/0x270 [jbd2]

which is not great. The crash happens because bh->b_private is suddently
NULL although BH_JBD flag is still set (this is because
block_invalidatepage() cleared BH_Mapped flag and subsequent bh lookup
found buffer without BH_Mapped set, called init_page_buffers() which has
rewritten bh->b_private). So just remove the invalidation in
block_write_full_page().

Note that the buffer cache invalidation when block device changes size
is already careful to avoid similar problems by using
invalidate_mapping_pages() which skips busy buffers so it was only this
odd block_write_full_page() behavior that could tear down bdev buffers
under filesystem's hands.
Reported-by: NYe Bin <yebin10@huawei.com>
Signed-off-by: NJan Kara <jack@suse.cz>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
CC: stable@vger.kernel.org
Signed-off-by: NJens Axboe <axboe@kernel.dk>

High CPU utilization on "native_queued_spin_lock_slowpath" due to lock
contention is possible for mq-deadline and bfq IO schedulers
when nr_hw_queues is more than one.

It is because kblockd work queue can submit IO from all online CPUs
(through blk_mq_run_hw_queues()) even though only one hctx has pending
commands.

The elevator callback .has_work for mq-deadline and bfq scheduler considers
pending work if there are any IOs on request queue but it does not account
hctx context.

Add a per-hctx 'elevator_queued' count to the hctx to avoid triggering
the elevator even though there are no requests queued.

[jpg: Relocated atomic_dec() in dd_dispatch_request(), update commit message per Kashyap]
Signed-off-by: NKashyap Desai <kashyap.desai@broadcom.com>
Signed-off-by: NHannes Reinecke <hare@suse.de>
Signed-off-by: NJohn Garry <john.garry@huawei.com>
Tested-by: NDouglas Gilbert <dgilbert@interlog.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

For when using a shared sbitmap, no longer should the number of active
request queues per hctx be relied on for when judging how to share the tag
bitmap.

Instead maintain the number of active request queues per tag_set, and make
the judgement based on that.

Originally-from: Kashyap Desai <kashyap.desai@broadcom.com>
Signed-off-by: NJohn Garry <john.garry@huawei.com>
Tested-by: Don Brace<don.brace@microsemi.com> #SCSI resv cmds patches used
Tested-by: NDouglas Gilbert <dgilbert@interlog.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

The per-hctx nr_active value can no longer be used to fairly assign a share
of tag depth per request queue for when using a shared sbitmap, as it does
not consider that the tags are shared tags over all hctx's.

For this case, record the nr_active_requests per request_queue, and make
the judgement based on that value.

Co-developed-with: Kashyap Desai <kashyap.desai@broadcom.com>
Signed-off-by: NJohn Garry <john.garry@huawei.com>
Tested-by: Don Brace<don.brace@microsemi.com> #SCSI resv cmds patches used
Tested-by: NDouglas Gilbert <dgilbert@interlog.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

blk-mq.h and blk-mq-tag.h include on each other, which is less than ideal.

Locate hctx_may_queue() to blk-mq.h, as it is not really tag specific code.

In this way, we can drop the blk-mq-tag.h include of blk-mq.h
Signed-off-by: NJohn Garry <john.garry@huawei.com>
Tested-by: NDouglas Gilbert <dgilbert@interlog.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Some SCSI HBAs (such as HPSA, megaraid, mpt3sas, hisi_sas_v3 ..) support
multiple reply queues with single hostwide tags.

In addition, these drivers want to use interrupt assignment in
pci_alloc_irq_vectors(PCI_IRQ_AFFINITY). However, as discussed in [0],
CPU hotplug may cause in-flight IO completion to not be serviced when an
interrupt is shutdown. That problem is solved in commit bf0beec0
("blk-mq: drain I/O when all CPUs in a hctx are offline").

However, to take advantage of that blk-mq feature, the HBA HW queuess are
required to be mapped to that of the blk-mq hctx's; to do that, the HBA HW
queues need to be exposed to the upper layer.

In making that transition, the per-SCSI command request tags are no
longer unique per Scsi host - they are just unique per hctx. As such, the
HBA LLDD would have to generate this tag internally, which has a certain
performance overhead.

However another problem is that blk-mq assumes the host may accept
(Scsi_host.can_queue * #hw queue) commands. In commit 6eb045e0 ("scsi:
 core: avoid host-wide host_busy counter for scsi_mq"), the Scsi host busy
counter was removed, which would stop the LLDD being sent more than
.can_queue commands; however, it should still be ensured that the block
layer does not issue more than .can_queue commands to the Scsi host.

To solve this problem, introduce a shared sbitmap per blk_mq_tag_set,
which may be requested at init time.

New flag BLK_MQ_F_TAG_HCTX_SHARED should be set when requesting the
tagset to indicate whether the shared sbitmap should be used.

Even when BLK_MQ_F_TAG_HCTX_SHARED is set, a full set of tags and requests
are still allocated per hctx; the reason for this is that if tags and
requests were only allocated for a single hctx - like hctx0 - it may break
block drivers which expect a request be associated with a specific hctx,
i.e. not always hctx0. This will introduce extra memory usage.

This change is based on work originally from Ming Lei in [1] and from
Bart's suggestion in [2].

[0] https://lore.kernel.org/linux-block/alpine.DEB.2.21.1904051331270.1802@nanos.tec.linutronix.de/
[1] https://lore.kernel.org/linux-block/20190531022801.10003-1-ming.lei@redhat.com/
[2] https://lore.kernel.org/linux-block/ff77beff-5fd9-9f05-12b6-826922bace1f@huawei.com/T/#m3db0a602f095cbcbff27e9c884d6b4ae826144beSigned-off-by: NJohn Garry <john.garry@huawei.com>
Tested-by: Don Brace<don.brace@microsemi.com> #SCSI resv cmds patches used
Tested-by: NDouglas Gilbert <dgilbert@interlog.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Introduce pointers for the blk_mq_tags regular and reserved bitmap tags,
with the goal of later being able to use a common shared tag bitmap across
all HW contexts in a set.
Signed-off-by: NJohn Garry <john.garry@huawei.com>
Tested-by: Don Brace<don.brace@microsemi.com> #SCSI resv cmds patches used
Tested-by: NDouglas Gilbert <dgilbert@interlog.com>
Reviewed-by: NHannes Reinecke <hare@suse.de>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Pass hctx/tagset flags argument down to blk_mq_init_tags() and
blk_mq_free_tags() for selective init/free.

For now, make it include the alloc policy flag, which can be evaluated
when needed (in blk_mq_init_tags()).
Signed-off-by: NJohn Garry <john.garry@huawei.com>
Tested-by: NDouglas Gilbert <dgilbert@interlog.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Since the tags are allocated in blk_mq_init_tags(), it's better practice
to free in that same function upon error, rather than a callee which is to
init the bitmap tags (blk_mq_init_tags()).

[jpg: Split from an earlier patch with a new commit message]
Signed-off-by: NHannes Reinecke <hare@suse.de>
Signed-off-by: NJohn Garry <john.garry@huawei.com>
Tested-by: NDouglas Gilbert <dgilbert@interlog.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

The function does not set the depth, but rather transitions from
shared to non-shared queues and vice versa.

So rename it to blk_mq_update_tag_set_shared() to better reflect
its purpose.

[jpg: take out some unrelated changes in blk_mq_init_bitmap_tags()]
Signed-off-by: NHannes Reinecke <hare@suse.de>
Signed-off-by: NJohn Garry <john.garry@huawei.com>
Tested-by: NDouglas Gilbert <dgilbert@interlog.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

BLK_MQ_F_TAG_SHARED actually means that tags is shared among request
queues, all of which should belong to LUNs attached to same HBA.

So rename it to make the point explicitly.

[jpg: rebase a few times, add rnbd-clt.c change]
Suggested-by: NBart Van Assche <bvanassche@acm.org>
Signed-off-by: NMing Lei <ming.lei@redhat.com>
Signed-off-by: NJohn Garry <john.garry@huawei.com>
Tested-by: NDouglas Gilbert <dgilbert@interlog.com>
Reviewed-by: NHannes Reinecke <hare@suse.de>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Remove the now unused helper.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NJosef Bacik <josef@toxicpanda.com>
Reviewed-by: NJohannes Thumshirn <johannes.thumshirn@wdc.com>
Acked-by: NSong Liu <song@kernel.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

The nvdimm block driver abuse revalidate_disk in a strange way, and
totally unrelated to what other drivers do.  Simplify this by just
calling nvdimm_revalidate_disk (which seems rather misnamed) from the
probe routines, as the additional bdev size revalidation is pointless
at this point, and remove the revalidate_disk methods given that
it can only be triggered from add_disk, which is right before the
manual calls.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NJosef Bacik <josef@toxicpanda.com>
Reviewed-by: NJohannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Instead of calling revalidate_disk just do the work directly by
calling sd_revalidate_disk, and revalidate_disk_size where needed.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NJosef Bacik <josef@toxicpanda.com>
Reviewed-by: NJohannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Keep control in the NVMe driver instead of going through an indirect
call back into ->revalidate_disk.  Also reorder the function a bit to be
easier to follow with the additional code.

And now that we have removed all callers of revalidate_disk() in the nvme
code, ->revalidate_disk is only called from the open code when first
opening the device.  Which is of course totally pointless as we have
a valid size since the initial scan, and will get an updated view
through the asynchronous notifiation everytime the size changes.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NJosef Bacik <josef@toxicpanda.com>
Reviewed-by: NJohannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Only virtio_blk and xen-blkfront set the revalidate argument to true,
and both do not implement the ->revalidate_disk method.  So switch
to the helper that just updates the size instead.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NJosef Bacik <josef@toxicpanda.com>
Reviewed-by: NJohannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

revalidate_disk is a relative awkward helper for driver use, as it first
calls an optional driver method and then updates the block device size,
while most callers either don't need the method call at all, or want to
keep state between the caller and the called method.

Add a revalidate_disk_size helper that just performs the update of the
block device size from the gendisk one, and switch all drivers that do
not implement ->revalidate_disk to use the new helper instead of
revalidate_disk()
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NJosef Bacik <josef@toxicpanda.com>
Reviewed-by: NJohannes Thumshirn <johannes.thumshirn@wdc.com>
Acked-by: NSong Liu <song@kernel.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Replace bd_invalidate with a new BDEV_NEED_PART_SCAN flag in a bd_flags
variable to better describe the condition.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NJosef Bacik <josef@toxicpanda.com>
Reviewed-by: NJohannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

bd_invalidated is set by check_disk_change or in add_disk to initiate a
partition scan.  Move it from check_disk_size_change which is called
from both revalidate_disk() and bdev_disk_changed() to only the latter,
as that is what is called from the block device open code (and nbd) to
deal with the bd_invalidated event.  revalidate_disk() on the other hand
is mostly used to propagate a size update from the gendisk to the block
device, which is entirely unrelated.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NJosef Bacik <josef@toxicpanda.com>
Reviewed-by: NJohannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

unlock_native_capacity is never called from check_disk_change(), and
while revalidate_disk can be called from it, it can also be called
from two other places at the moment.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NJosef Bacik <josef@toxicpanda.com>
Reviewed-by: NJohannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Remove a duplicative condition to remove below cppcheck warnings:

"warning: Redundant condition: sched_allow_merge. '!A || (A && B)' is
equivalent to '!A || B' [redundantCondition]"
Reported-by: Nkernel test robot <lkp@intel.com>
Signed-off-by: NBaolin Wang <baolin.wang@linux.alibaba.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

If WRITE_ZERO/WRITE_SAME operation is not supported by the storage,
blk_cloned_rq_check_limits() will return IO error which will cause
device-mapper to fail the paths.

Instead, if the queue limit is set to 0, return BLK_STS_NOTSUPP.
BLK_STS_NOTSUPP will be ignored by device-mapper and will not fail the
paths.
Suggested-by: NMartin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: NRitika Srivastava <ritika.srivastava@oracle.com>
Reviewed-by: NMartin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Replace returning legacy errno codes with blk_status_t in
blk_cloned_rq_check_limits().
Signed-off-by: NRitika Srivastava <ritika.srivastava@oracle.com>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

CAP_SYS_ADMIN is too broad, and ionice fits into CAP_SYS_NICE's grouping.

Retain CAP_SYS_ADMIN permission for backwards compatibility.
Signed-off-by: NKhazhismel Kumykov <khazhy@google.com>
Reviewed-by: NBart Van Assche <bvanassche@acm.org>
Acked-by: NSerge Hallyn <serge@hallyn.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

iocost went through significant internal changes. Update iocost_monitor.py
accordingly.
Signed-off-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

These are really cheap to collect and can be useful in debugging iocost
behavior. Add them as debug stats for now.
Signed-off-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Update and restore the inuse update tracepoints.
Signed-off-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

When an iocg accumulates too much vtime or gets deactivated, we throw away
some vtime, which lowers the overall device utilization. As the exact amount
which is being thrown away is known, we can compensate by accelerating the
vrate accordingly so that the extra vtime generated in the current period
matches what got lost.

This significantly improves work conservation when involving high weight
cgroups with intermittent and bursty IO patterns.
Signed-off-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

A low weight iocg can amass a large amount of debt, for example, when
anonymous memory gets reclaimed aggressively. If the system has a lot of
memory paired with a slow IO device, the debt can span multiple seconds or
more. If there are no other subsequent IO issuers, the in-debt iocg may end
up blocked paying its debt while the IO device is idle.

This patch implements a mechanism to protect against such pathological
cases. If the device has been sufficiently idle for a substantial amount of
time, the debts are halved. The criteria are on the conservative side as we
want to resolve the rare extreme cases without impacting regular operation
by forgiving debts too readily.
Signed-off-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Curently, iocost syncs the delay duration to the outstanding debt amount,
which seemed enough to protect the system from anon memory hogs. However,
that was mostly because the delay calcuation was using hweight_inuse which
quickly converges towards zero under debt for delay duration calculation,
often pusnishing debtors overly harshly for longer than deserved.

The previous patch fixed the delay calcuation and now the protection against
anonymous memory hogs isn't enough because the effect of delay is indirect
and non-linear and a huge amount of future debt can accumulate abruptly
while unthrottled.

This patch implements delay hysteresis so that delay is decayed
exponentially over time instead of getting cleared immediately as debt is
paid off. While the overall behavior is similar to the blk-cgroup
implementation used by blk-iolatency, a lot of the details are different and
due to the empirical nature of the mechanism, it's challenging to adapt the
mechanism for one controller without negatively impacting the other.

As the delay is gradually decayed now, there's no point in running it from
its own hrtimer. Periodic updates are now performed from ioc_timer_fn() and
the dedicated hrtimer is removed.
Signed-off-by: NTejun Heo <tj@kernel.org>
Cc: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Debt handling had several issues.

* How much inuse a debtor carries wasn't clearly defined. inuse would be
  driven down over time from not issuing IOs but it'd be better to clamp it
  to minimum immediately once in debt.

* How much can be paid off was determined by hweight_inuse. As inuse was
  driven down, the payment amount would fall together regardless of the
  debtor's active weight. This means that the debtors were punished harshly.

* ioc_rqos_merge() wasn't calling blkcg_schedule_throttle() after
  iocg_kick_delay().

This patch revamps debt handling so that

* Debt handling owns inuse for iocgs in debt and keeps them at zero.

* Payment amount is determined by hweight_active. This is more deterministic
  and safer than hweight_inuse but still far from ideal in that it doesn't
  factor in possible donations from other iocgs for debt payments. This
  likely needs further improvements in the future.

* iocg_rqos_merge() now calls blkcg_schedule_throttle() as necessary.
Signed-off-by: NTejun Heo <tj@kernel.org>
Cc: Andy Newell <newella@fb.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

When the margin drops below the minimum on a donating iocg, donation is
immediately canceled in full. There are a couple shortcomings with the
current behavior.

* It's abrupt. A small temporary budget deficit can lead to a wide swing in
  weight allocation and a large surplus.

* It's open coded in the issue path but not implemented for the merge path.
  A series of merges at a low inuse can make the iocg incur debts and stall
  incorrectly.

This patch reimplements in-period donation snapbacks so that

* inuse adjustment and cost calculations are factored into
  adjust_inuse_and_calc_cost() which is called from both the issue and merge
  paths.

* Snapbacks are more gradual. It occurs in quarter steps.

* A snapback triggers if the margin goes below the low threshold and is
  lower than the budget at the time of the last adjustment.

* For the above, __propagate_weights() stores the margin in
  iocg->saved_margin. Move iocg->last_inuse storing together into
  __propagate_weights() for consistency.

* Full snapback is guaranteed when there are waiters.

* With precise donation and gradual snapbacks, inuse adjustments are now a
  lot more effective and the value of scaling inuse on weight changes isn't
  clear. Removed inuse scaling from weight_update().
Signed-off-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

iocost has various safety nets to combat inuse adjustment calculation
inaccuracies. With Andy's method implemented in transfer_surpluses(), inuse
adjustment calculations are now accurate and we can make donation amount
determinations accurate too.

* Stop keeping track of past usage history and using the maximum. Act on the
  immediate usage information.

* Remove donation constraints defined by SURPLUS_* constants. Donate
  whatever isn't used.

* Determine the donation amount so that the iocg will end up with
  MARGIN_TARGET_PCT budget at the end of the coming period assuming the same
  usage as the previous period. TARGET is set at 50% of period, which is the
  previous maximum. This provides smooth convergence for most repetitive IO
  patterns.

* Apply donation logic early at 20% budget. There's no risk in doing so as
  the calculation is based on the delta between the current budget and the
  target budget at the end of the coming period.

* Remove preemptive iocg activation for zero cost IOs. As donation can reach
  near zero now, the mere activation doesn't provide any protection anymore.
  In the unlikely case that this becomes a problem, the right solution is
  assigning appropriate costs for such IOs.

This significantly improves the donation determination logic while also
simplifying it. Now all donations are immediate, exact and smooth.
Signed-off-by: NTejun Heo <tj@kernel.org>
Cc: Andy Newell <newella@fb.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

iocost implements work conservation by reducing iocg->inuse and propagating
the adjustment upwards proportionally. However, while I knew the target
absolute hierarchical proportion - adjusted hweight_inuse, I couldn't figure
out how to determine the iocg->inuse adjustment to achieve that and
approximated the adjustment by scaling iocg->inuse using the proportion of
the needed hweight_inuse changes.

When nested, these scalings aren't accurate even when adjusting a single
node as the donating node also receives the benefit of the donated portion.
When multiple nodes are donating as they often do, they can be wildly wrong.

iocost employed various safety nets to combat the inaccuracies. There are
ample buffers in determining how much to donate, the adjustments are
conservative and gradual. While it can achieve a reasonable level of work
conservation in simple scenarios, the inaccuracies can easily add up leading
to significant loss of total work. This in turn makes it difficult to
closely cap vrate as vrate adjustment is needed to compensate for the loss
of work. The combination of inaccurate donation calculations and vrate
adjustments can lead to wide fluctuations and clunky overall behaviors.

Andy Newell devised a method to calculate the needed ->inuse updates to
achieve the target hweight_inuse's. The method is compatible with the
proportional inuse adjustment propagation which allows all hot path
operations to be local to each iocg.

To roughly summarize, Andy's method divides the tree into donating and
non-donating parts, calculates global donation rate which is used to
determine the target hweight_inuse for each node, and then derives per-level
proportions. There's non-trivial amount of math involved. Please refer to
the following pdfs for detailed descriptions.

  https://drive.google.com/file/d/1PsJwxPFtjUnwOY1QJ5AeICCcsL7BM3bo
  https://drive.google.com/file/d/1vONz1-fzVO7oY5DXXsLjSxEtYYQbOvsE
  https://drive.google.com/file/d/1WcrltBOSPN0qXVdBgnKm4mdp9FhuEFQN

This patch implements Andy's method in transfer_surpluses(). This makes the
donation calculations accurate per cycle and enables further improvements in
other parts of the donation logic.
Signed-off-by: NTejun Heo <tj@kernel.org>
Cc: Andy Newell <newella@fb.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

The way the surplus donation logic is structured isn't great. There are two
separate paths for starting/increasing donations and decreasing them making
the logic harder to follow and is prone to unnecessary behavior differences.

In preparation for improved donation handling, this patch restructures the
code so that

* All donors - new, increasing and decreasing - are funneled through the
  same code path.

* The target donation calculation is factored into hweight_after_donation()
  which is called once from the same spot for all possible donors.

* Actual inuse adjustment is factored into trasnfer_surpluses().

This change introduces a few behavior differences - e.g. donation amount
reduction now uses the max usage of the recent three periods just like new
and increasing donations, and inuse now gets adjusted upwards the same way
it gets downwards. These differences are unlikely to have severely negative
implications and the whole logic will be revamped soon.

This patch also removes two tracepoints. The existing TPs don't quite fit
the new implementation. A later patch will update and reinstate them.
Signed-off-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>