On 15.10.20 16:24, Roger Pau Monne wrote:
Assume that reads and writes to the variable will be atomic. The worse that could happen is that one of the purges removes a partially written percentage of grants, but the cache itself will recover.Signed-off-by: Roger Pau Monné <roger....@citrix.com> --- Cc: Konrad Rzeszutek Wilk <konrad.w...@oracle.com> Cc: Jens Axboe <ax...@kernel.dk> Cc: Boris Ostrovsky <boris.ostrov...@oracle.com> Cc: SeongJae Park <sjp...@amazon.de> Cc: xen-de...@lists.xenproject.org Cc: linux-bl...@vger.kernel.org Cc: J. Roeleveld <jo...@antarean.org> Cc: Jürgen Groß <jgr...@suse.com> --- Documentation/ABI/testing/sysfs-driver-xen-blkback | 9 +++++++++ drivers/block/xen-blkback/blkback.c | 7 +++++-- 2 files changed, 14 insertions(+), 2 deletions(-) diff --git a/Documentation/ABI/testing/sysfs-driver-xen-blkback b/Documentation/ABI/testing/sysfs-driver-xen-blkback index 776f25d335ca..7de791ad61f9 100644 --- a/Documentation/ABI/testing/sysfs-driver-xen-blkback +++ b/Documentation/ABI/testing/sysfs-driver-xen-blkback @@ -45,3 +45,12 @@ Description: to be executed periodically. This parameter controls the time interval between consecutive executions of the purge mechanism is set in ms. + +What: /sys/module/xen_blkback/parameters/lru_percent_clean +Date: October 2020 +KernelVersion: 5.10 +Contact: Roger Pau Monné <roger....@citrix.com> +Description: + When the persistent grants list is full we will remove unused + grants from the list. The percent number of grants to be + removed at each LRU execution. diff --git a/drivers/block/xen-blkback/blkback.c b/drivers/block/xen-blkback/blkback.c index 6ad9b76fdb2b..772852d45a5a 100644 --- a/drivers/block/xen-blkback/blkback.c +++ b/drivers/block/xen-blkback/blkback.c @@ -127,7 +127,10 @@ MODULE_PARM_DESC(lru_internval, * from the list. The percent number of grants to be removed at each LRU * execution. */ -#define LRU_PERCENT_CLEAN 5 +static unsigned int lru_percent_clean = 5; +module_param_named(lru_percent_clean, lru_percent_clean, uint, 0644); +MODULE_PARM_DESC(lru_percent_clean, + "Percentage of persistent grants to remove from the cache when full");/* Run-time switchable: /sys/module/blkback/parameters/ */static unsigned int log_stats; @@ -404,7 +407,7 @@ static void purge_persistent_gnt(struct xen_blkif_ring *ring) !ring->blkif->vbd.overflow_max_grants)) { num_clean = 0; } else { - num_clean = (max_pgrants / 100) * LRU_PERCENT_CLEAN; + num_clean = (max_pgrants / 100) * lru_percent_clean;
Hmm, wouldn't it be better to use (max_grants * lru_percent_clean) / 100 here in order to support max_grants values less than 100? Juergen
