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@xxxxxxxxxx/) - 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@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 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@xxxxxxxxx/) - Drop 'Reviewed-by: Juergen' from the second patch (suggested by Roger Pau Monné) - Update contact of the new module param to SeongJae Park <sjpark@xxxxxxxxx> (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@xxxxxxxxx/) - 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@xxxxxxxxx/) - 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@xxxxxxxxx/) - 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@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 | 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
