On Thu, Oct 15, 2020 at 04:37:52PM +0200, Jürgen Groß wrote:
> 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.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 | 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.pau@xxxxxxxxxx>
> > +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?
Yes, we should have done that when moving max_pgrants to a parameter,
it used to be fixed first.
Will do in next version since I'm already changing the line.
Thanks, Roger.
