Messages in this thread | | | Subject | Re: [PATCH 2/2] xen/blkback: turn the cache purge percent into a parameter | From | Jürgen Groß <> | Date | Thu, 15 Oct 2020 16:37:52 +0200 |
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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@citrix.com> > --- > Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> > Cc: Jens Axboe <axboe@kernel.dk> > Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com> > Cc: SeongJae Park <sjpark@amazon.de> > Cc: xen-devel@lists.xenproject.org > Cc: linux-block@vger.kernel.org > Cc: J. Roeleveld <joost@antarean.org> > Cc: Jürgen Groß <jgross@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.pau@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
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