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In some use cases[1], the backend is created while the frontend doesn't
support the persistent grants feature, but later the frontend can be
changed to support the feature and reconnect. In the past, 'blkback'
enabled the persistent grants feature since it unconditionally checked
if frontend supports the persistent grants feature for every connect
('connect_ring()') and decided whether it should use persistent grans or
not.
However, commit aac8a70db2 ("xen-blkback: add a parameter for
disabling of persistent grants") has mistakenly changed the behavior.
It made the frontend feature support check to not be repeated once it
shown the 'feature_persistent' as 'false', or the frontend doesn't
support persistent grants.
This commit changes the behavior of the parameter to make effect for
every connect, so that the previous workflow can work again as expected.
[1] https://lore.kernel.org/xen-devel/CAJwUmVB6H3iTs-C+U=v-pwJB7-_ZRHPxHzKRJZ22xEPW7z8a=g@mail.gmail.com/
Reported-by: Andrii Chepurnyi <andrii.chepurnyi82@gmail.com>
Fixes: aac8a70db2 ("xen-blkback: add a parameter for disabling of persistent grants")
Cc: <stable@vger.kernel.org> # 5.10.x
Signed-off-by: Maximilian Heyne <mheyne@amazon.de>
Signed-off-by: SeongJae Park <sj@kernel.org>
Reviewed-by: Maximilian Heyne <mheyne@amazon.de>
Reviewed-by: Juergen Gross <jgross@suse.com>
Link: https://lore.kernel.org/r/20220715225108.193398-3-sj@kernel.org
Signed-off-by: Juergen Gross <jgross@suse.com>
47 lines
1.9 KiB
Plaintext
47 lines
1.9 KiB
Plaintext
What: /sys/module/xen_blkback/parameters/max_buffer_pages
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Date: March 2013
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KernelVersion: 3.11
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Contact: Roger Pau Monné <roger.pau@citrix.com>
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Description:
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Maximum number of free pages to keep in each block
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backend buffer.
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What: /sys/module/xen_blkback/parameters/max_persistent_grants
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Date: March 2013
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KernelVersion: 3.11
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Contact: Roger Pau Monné <roger.pau@citrix.com>
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Description:
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Maximum number of grants to map persistently in
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blkback. If the frontend tries to use more than
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max_persistent_grants, the LRU kicks in and starts
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removing 5% of max_persistent_grants every 100ms.
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What: /sys/module/xen_blkback/parameters/persistent_grant_unused_seconds
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Date: August 2018
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KernelVersion: 4.19
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Contact: Roger Pau Monné <roger.pau@citrix.com>
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Description:
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How long a persistent grant is allowed to remain
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allocated without being in use. The time is in
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seconds, 0 means indefinitely long.
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The default is 60 seconds.
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What: /sys/module/xen_blkback/parameters/buffer_squeeze_duration_ms
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Date: December 2019
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KernelVersion: 5.6
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Contact: Maximilian Heyne <mheyne@amazon.de>
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Description:
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When memory pressure is reported to blkback this option
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controls the duration in milliseconds that blkback will not
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cache any page not backed by a grant mapping.
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The default is 10ms.
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What: /sys/module/xen_blkback/parameters/feature_persistent
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Date: September 2020
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KernelVersion: 5.10
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Contact: Maximilian Heyne <mheyne@amazon.de>
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Description:
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Whether to enable the persistent grants feature or not. Note
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that this option only takes effect on newly connected backends.
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The default is Y (enable).
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