Re: [Xen-devel] [PATCH v13 0/5] xenbus/backend: Add memory pressure handler callback

[SeongJae Park <sjpark@amazon.com>]

Every patch of this patchset got at least one 'Reviewed-by' or 'Acked-by' from
appropriate maintainers by last Wednesday, and after that, got no comment yet.
May I ask some more comments?


Thanks,
SeongJae Park

On Wed, 18 Dec 2019 19:37:13 +0100 SeongJae Park <sjpark@amazon.com> wrote:

> 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 patches 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/v13
> 
> 
> Patch History
> -------------
> 
> Changes from v12
> (https://lore.kernel.org/xen-devel/20191218104232.9606-1-sjpark@amazon.com/)
>  - Do not unnecessarily disable interrupts (suggested by Juergen)
>  - Hold lock from xenbus side (suggested by Juergen)
> 
> Changes from v11
> (https://lore.kernel.org/xen-devel/20191217160748.693-2-sjpark@amazon.com/)
>  - 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@amazon.com/)
>  - Fix race condition (reported by SeongJae, suggested by Juergen)
> 
> Changes from v9
> (https://lore.kernel.org/xen-devel/20191213153546.17425-1-sjpark@amazon.de/)
>  - Add 'Reviewed-by' and 'Acked-by' from Roger Pau Monné
>  - Update the commit message for overhead test of the 2nd path
> 
> Changes from v8
> (https://lore.kernel.org/xen-devel/20191213130211.24011-1-sjpark@amazon.de/)
>  - Drop 'Reviewed-by: Juergen' from the second patch
>    (suggested by Roger Pau Monné)
>  - Update contact of the new module param to SeongJae Park
>    <sjpark@amazon.de>
>    (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
> (https://lore.kernel.org/xen-devel/20191211181016.14366-1-sjpark@amazon.de/)
>  - 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
> (https://lore.kernel.org/linux-block/20191211042428.5961-1-sjpark@amazon.de/)
>  - 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
> (https://lore.kernel.org/linux-block/20191210080628.5264-1-sjpark@amazon.de/)
>  - Wordsmith the commit messages (suggested by Roger Pau Monné)
>  - Change the reclaim callback return type (suggested by Roger Pau
>    Monné)
>  - 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 checkpatch.pl warnings
> 
> Changes from v4
> (https://lore.kernel.org/xen-devel/20191209194305.20828-1-sjpark@amazon.com/)
>  - 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@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 (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            | 28 ++++++++++---
>  drivers/xen/xenbus/xenbus_probe.c             |  8 +++-
>  drivers/xen/xenbus/xenbus_probe_backend.c     | 38 +++++++++++++++++
>  include/xen/xenbus.h                          |  3 ++
>  7 files changed, 103 insertions(+), 27 deletions(-)
> 
> -- 
> 2.17.1
>