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Re: [PATCH 1/2] xen/blkback: turn the cache purge LRU interval into a parameter

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 LRU intervals is not calculated
properly if a partially written value is read, but that would only be
a transient issue.

Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Cc: Jens Axboe <axboe@xxxxxxxxx>
Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Cc: SeongJae Park <sjpark@xxxxxxxxx>
Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx
Cc: linux-block@xxxxxxxxxxxxxxx
Cc: J. Roeleveld <joost@xxxxxxxxxxxx>
Cc: Jürgen Groß <jgross@xxxxxxxx>
  Documentation/ABI/testing/sysfs-driver-xen-blkback | 10 ++++++++++
  drivers/block/xen-blkback/blkback.c                |  9 ++++++---
  2 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/Documentation/ABI/testing/sysfs-driver-xen-blkback 
index ecb7942ff146..776f25d335ca 100644
--- a/Documentation/ABI/testing/sysfs-driver-xen-blkback
+++ b/Documentation/ABI/testing/sysfs-driver-xen-blkback
@@ -35,3 +35,13 @@ Description:
                  controls the duration in milliseconds that blkback will not
                  cache any page not backed by a grant mapping.
                  The default is 10ms.
+What:           /sys/module/xen_blkback/parameters/lru_internval


+Date:           October 2020
+KernelVersion:  5.10
+Contact:        Roger Pau Monné <roger.pau@xxxxxxxxxx>
+                The LRU mechanism to clean the lists of persistent grants needs
+                to be executed periodically. This parameter controls the time
+                interval between consecutive executions of the purge mechanism
+                is set in ms.
diff --git a/drivers/block/xen-blkback/blkback.c 
index adfc9352351d..6ad9b76fdb2b 100644
--- a/drivers/block/xen-blkback/blkback.c
+++ b/drivers/block/xen-blkback/blkback.c
@@ -117,7 +117,10 @@ MODULE_PARM_DESC(max_ring_page_order, "Maximum order of 
pages to be used for the
   * be executed periodically. The time interval between consecutive executions
   * of the purge mechanism is set in ms.
-#define LRU_INTERVAL 100
+static unsigned int lru_interval = 100;
+module_param_named(lru_interval, lru_interval, uint, 0644);


+                "Time interval between consecutive executions of the cache purge 
mechanism (in ms)");
   * When the persistent grants list is full we will remove unused grants
@@ -620,7 +623,7 @@ int xen_blkif_schedule(void *arg)
                if (unlikely(vbd->size != vbd_sz(vbd)))
- timeout = msecs_to_jiffies(LRU_INTERVAL);
+               timeout = msecs_to_jiffies(lru_interval);
timeout = wait_event_interruptible_timeout(
@@ -650,7 +653,7 @@ int xen_blkif_schedule(void *arg)
                if (blkif->vbd.feature_gnt_persistent &&
                    time_after(jiffies, ring->next_lru)) {
-                       ring->next_lru = jiffies + 
+                       ring->next_lru = jiffies + 
/* Shrink the free pages pool if it is too large. */




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