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Subject[PATCH v10 0/4] xenbus/backend: Add a memory pressure handler callback
Granting pages consumes backend system memory.  In systems configured
with insufficient spare memory for those pages, it can cause a memory
pressure situation. However, finding the optimal amount of the spare
memory is challenging for large systems having dynamic resource
utilization patterns. Also, such a static configuration might lack

To mitigate such problems, this patchset adds a memory reclaim callback
to 'xenbus_driver' (patch 1) and use it to mitigate the problem in
'xen-blkback' (patch 2). The third and fourth patches are trivial

Base Version

This patch is based on v5.4. A complete tree is also available at my
public git repo:

Patch History

Changes from v9
- Add 'Reviewed-by' and 'Acked-by' from Roger Pau Monné
- Update the commit message for overhead test of the 2nd path

Changes from v8
- Drop 'Reviewed-by: Juergen' from the second patch
(suggested by Roger Pau Monné)
- Update contact of the new module param to SeongJae Park
(suggested by Roger Pau Monné)
- Wordsmith the description of the parameter
(suggested by Roger Pau Monné)
- Fix dumb bugs
(suggested by Roger Pau Monné)
- Move module param definition to xenbus.c and reduce the number of
lines for this change
(suggested by Roger Pau Monné)
- Add a comment for the new callback, reclaim_memory, as other
callbacks also have
- Add another trivial cleanup of xenbus.c file (4th patch)

Changes from v7
- Update sysfs-driver-xen-blkback for new parameter
(suggested by Roger Pau Monné)
- Use per-xen_blkif buffer_squeeze_end instead of global variable
(suggested by Roger Pau Monné)

Changes from v6
- Remove more unnecessary prefixes (suggested by Roger Pau Monné)
- Constify a variable (suggested by Roger Pau Monné)
- Rename 'reclaim' into 'reclaim_memory' (suggested by Roger Pau Monné)
- More wordsmith of the commit message (suggested by Roger Pau Monné)

Changes from v5
- Wordsmith the commit messages (suggested by Roger Pau Monné)
- Change the reclaim callback return type (suggested by Roger Pau
- Change the type of the blkback squeeze duration variable
(suggested by Roger Pau Monné)
- Add a patch for removal of unnecessary static variable name prefixes
(suggested by Roger Pau Monné)
- Fix warnings

Changes from v4
- Remove domain id parameter from the callback (suggested by Juergen
- Rename xen-blkback module parameter (suggested by Stefan Nuernburger)

Changes from v3
- Add general callback in xen_driver and use it (suggested by Juergen

Changes from v2
- Rename the module parameter and variables for brevity
(aggressive shrinking -> squeezing)

Changes from v1
- Adjust the description to not use the term, `arbitrarily`
(suggested by Paul Durrant)
- Specify time unit of the duration in the parameter description,
(suggested by Maximilian Heyne)
- Change default aggressive shrinking duration from 1ms to 10ms
- Merge two patches into one single patch

SeongJae Park (4):
xenbus/backend: Add memory pressure handler callback
xen/blkback: Squeeze page pools if a memory pressure is detected
xen/blkback: Remove unnecessary static variable name prefixes
xen/blkback: Consistently insert one empty line between functions

.../ABI/testing/sysfs-driver-xen-blkback | 10 +++++
drivers/block/xen-blkback/blkback.c | 42 +++++++++----------
drivers/block/xen-blkback/common.h | 1 +
drivers/block/xen-blkback/xenbus.c | 26 +++++++++---
drivers/xen/xenbus/xenbus_probe_backend.c | 32 ++++++++++++++
include/xen/xenbus.h | 1 +
6 files changed, 86 insertions(+), 26 deletions(-)


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