[PATCH v5 0/2] xenbus/backend: Add a memory pressure handler callback

[SeongJae Park <sj38.park@gmail.com>]

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 a
flexibility.

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).

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/blkback_squeezing_v5


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

Changes from v4
(https://lore.kernel.org/xen-devel/20191209194305.20828-1-sjpark@amazon.com/)
 - Remove domain id parameter from the callback (suggested by Jergen Gross)

Changes from v3
(https://lore.kernel.org/xen-devel/20191209085839.21215-1-sjpark@amazon.com/)
 - 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@amazon.com)
 - Rename the module parameter and variables for brevity (aggressive
   shrinking -> squeezing)

Changes from v1
(https://lore.kernel.org/xen-devel/20191204113419.2298-1-sjpark@amazon.com/)
 - 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 (2):
  xenbus/backend: Add memory pressure handler callback
  xen/blkback: Squeeze page pools if a memory pressure is detected

 drivers/block/xen-blkback/blkback.c       | 23 +++++++++++++++--
 drivers/block/xen-blkback/common.h        |  1 +
 drivers/block/xen-blkback/xenbus.c        |  3 ++-
 drivers/xen/xenbus/xenbus_probe_backend.c | 31 +++++++++++++++++++++++
 include/xen/xenbus.h                      |  1 +
 5 files changed, 56 insertions(+), 3 deletions(-)

-- 
2.17.1