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[6.6] bcache IO hinting updates #32

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[6.6] bcache IO hinting updates #32

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Commits on Nov 19, 2023

  1. bcache: introduce bcache sysfs entries for ioprio-based bypass/writeb… 

    …ack hints

Add sysfs entries to support to hint for bypass/writeback by the ioprio
assigned to the bio.  If the bio is unassigned, use current's io-context
ioprio for cache writeback or bypass (configured per-process with
`ionice`).

Having idle IOs bypass the cache can increase performance elsewhere
since you probably don't care about their performance.  In addition,
this prevents idle IOs from promoting into (polluting) your cache and
evicting blocks that are more important elsewhere.

If you really nead the performance at the expense of SSD wearout,
then configure ioprio_writeback and set your `ionice` appropriately.

For example:
	echo 2,7 > /sys/block/bcache0/bcache/ioprio_bypass
	echo 2,0 > /sys/block/bcache0/bcache/ioprio_writeback

See the documentation commit for details.

v2: Removed calls to get_task_io_context()

Signed-off-by: Eric Wheeler <[email protected]>
Acked-by: Kent Overstreet <[email protected]>
Tested-by: Kai Krakow <[email protected]>
Cc: [email protected]
Signed-off-by: Kai Krakow <[email protected]>
    @kakra
    Eric Wheeler authored and kakra committed Nov 19, 2023
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  2. bcache: documentation for sysfs entries describing bcache cache hinting 

    v2: get_task_io_context() no longer exists in the kernel

Signed-off-by: Eric Wheeler <[email protected]>
Signed-off-by: Kai Krakow <[email protected]>
    @kakra
    Eric Wheeler authored and kakra committed Nov 19, 2023
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  3. bcache: Only skip data request in io_prio bypass mode 

    Even if ioprio_bypass hints bypassing the request, we still allow it
for REQ_META|REQ_PRIO bio.

Cc: Eric Wheeler <[email protected]>
Signed-off-by: Kai Krakow <[email protected]>
    @kakra
    kakra committed Nov 19, 2023
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