[PATCH v12 0/5] xenbus/backend: Add memory pressure handler callback

From: SeongJae Park
Date: Wed Dec 18 2019 - 05:43:08 EST


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
flexibility.

To mitigate such problems, this patchset adds a memory reclaim callback
to 'xenbus_driver' (patch 1) and then introduce a lock for race
condition avoidance (patch 2). After that, patch 3 applies the callback
mechanism to mitigate the problem in 'xen-blkback'. The fourth and
fifth patches are trivial cleanups; those fix nits we found during the
development of this patchset.

Note that patch 1, 4, and 5 are not changed since v9.


Base Version
------------

This patch is based on v5.4. A complete tree is also available at my
public git repo:
https://github.com/sjp38/linux/tree/patches/blkback/buffer_squeeze/v12


Patch History
-------------

Changes from v11
(https://lore.kernel.org/xen-devel/20191217160748.693-2-sjpark@xxxxxxxxxx/)
- Fix wrong trylock use (reported by Juergen)
- Merge patch 3 and 4 (suggested by Juergen)
- Update test result

Changes from v10
(https://lore.kernel.org/xen-devel/20191216124527.30306-1-sjpark@xxxxxxxxxx/)
- Fix race condition (reported by SeongJae, suggested by Juergen)

Changes from v9
(https://lore.kernel.org/xen-devel/20191213153546.17425-1-sjpark@xxxxxxxxx/)
- Add 'Reviewed-by' and 'Acked-by' from Roger Pau MonnÃ
- Update the commit message for overhead test of the 2nd path

Changes from v8
(https://lore.kernel.org/xen-devel/20191213130211.24011-1-sjpark@xxxxxxxxx/)
- Drop 'Reviewed-by: Juergen' from the second patch
(suggested by Roger Pau MonnÃ)
- Update contact of the new module param to SeongJae Park
<sjpark@xxxxxxxxx>
(suggested by Roger Pau MonnÃ)
- Wordsmith the description of the parameter
(suggested by Roger Pau MonnÃ)
- Fix dumb bugs
(suggested by Roger Pau MonnÃ)
- Move module param definition to xenbus.c and reduce the number of
lines for this change
(suggested by Roger Pau MonnÃ)
- 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
(https://lore.kernel.org/xen-devel/20191211181016.14366-1-sjpark@xxxxxxxxx/)
- Update sysfs-driver-xen-blkback for new parameter
(suggested by Roger Pau MonnÃ)
- Use per-xen_blkif buffer_squeeze_end instead of global variable
(suggested by Roger Pau MonnÃ)

Changes from v6
(https://lore.kernel.org/linux-block/20191211042428.5961-1-sjpark@xxxxxxxxx/)
- Remove more unnecessary prefixes (suggested by Roger Pau MonnÃ)
- Constify a variable (suggested by Roger Pau MonnÃ)
- Rename 'reclaim' into 'reclaim_memory' (suggested by Roger Pau MonnÃ)
- More wordsmith of the commit message (suggested by Roger Pau MonnÃ)

Changes from v5
(https://lore.kernel.org/linux-block/20191210080628.5264-1-sjpark@xxxxxxxxx/)
- Wordsmith the commit messages (suggested by Roger Pau MonnÃ)
- Change the reclaim callback return type (suggested by Roger Pau
MonnÃ)
- Change the type of the blkback squeeze duration variable
(suggested by Roger Pau MonnÃ)
- Add a patch for removal of unnecessary static variable name prefixes
(suggested by Roger Pau MonnÃ)
- Fix checkpatch.pl warnings

Changes from v4
(https://lore.kernel.org/xen-devel/20191209194305.20828-1-sjpark@xxxxxxxxxx/)
- Remove domain id parameter from the callback (suggested by Juergen
Gross)
- Rename xen-blkback module parameter (suggested by Stefan Nuernburger)

Changes from v3
(https://lore.kernel.org/xen-devel/20191209085839.21215-1-sjpark@xxxxxxxxxx/)
- Add general callback in xen_driver and use it (suggested by Juergen
Gross)

Changes from v2
(https://lore.kernel.org/linux-block/af195033-23d5-38ed-b73b-f6e2e3b34541@xxxxxxxxxx)
- Rename the module parameter and variables for brevity
(aggressive shrinking -> squeezing)

Changes from v1
(https://lore.kernel.org/xen-devel/20191204113419.2298-1-sjpark@xxxxxxxxxx/)
- 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 (5):
xenbus/backend: Add memory pressure handler callback
xenbus/backend: Protect xenbus callback with lock
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 | 37 +++++++++++++---
drivers/xen/xenbus/xenbus_probe.c | 1 +
drivers/xen/xenbus/xenbus_probe_backend.c | 39 +++++++++++++++++
include/xen/xenbus.h | 3 ++
7 files changed, 107 insertions(+), 26 deletions(-)

--
2.17.1