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). Those two patches could be merged into one patch if necessary. The third patch applies the callback mechanism to mitigate the problem in 'xen-blkback' (patch 3), but it lacks use of the race condition mitigation. Following change (patch 4) applies the race protection mechanism to the blkback. Patch 3 and patch 4 has seperated for only review convenience. Highly recommend to merge those into one patch as patch 3 applied version might confuse bisecting. The fifth and sixth patches are trivial cleanups; those fix nits we found during the development of this patchset. Note that patch 1, 3, 5, 6 are same with previous version. I made the changes in this version to different commits (only second and fourth patches) to make review more comfortable. Especially, the third and fourth patches should be merged into one patch, as the third one alone might make bisecting confuse. Tthe next version of this patchset will also merge those. 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/v11 Patch History ------------- 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 (6): 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: Protect 'reclaim_memory()' with 'reclaim_lock' 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 | 38 +++++++++++++++++ include/xen/xenbus.h | 3 ++ 7 files changed, 106 insertions(+), 26 deletions(-) -- 2.17.1
