From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Subject: Re: [PATCH 2/4] xen/blkfront: cleanup stale persistent grants To: =?UTF-8?Q?Roger_Pau_Monn=c3=a9?= Cc: linux-kernel@vger.kernel.org, xen-devel@lists.xenproject.org, linux-block@vger.kernel.org, konrad.wilk@oracle.com, axboe@kernel.dk, boris.ostrovsky@oracle.com References: <20180806113403.24728-1-jgross@suse.com> <20180806113403.24728-4-jgross@suse.com> <20180806161638.nmjamflckekeuyzb@mac> <20180807141404.lzsqtdd2seqgwtgx@mac> From: Juergen Gross Message-ID: Date: Tue, 7 Aug 2018 17:56:38 +0200 MIME-Version: 1.0 In-Reply-To: <20180807141404.lzsqtdd2seqgwtgx@mac> Content-Type: text/plain; charset=utf-8 List-ID: On 07/08/18 16:14, Roger Pau Monné wrote: > On Tue, Aug 07, 2018 at 08:31:31AM +0200, Juergen Gross wrote: >> On 06/08/18 18:16, Roger Pau Monné wrote: >>> On Mon, Aug 06, 2018 at 01:34:01PM +0200, Juergen Gross wrote: >>>> Add a periodic cleanup function to remove old persistent grants which >>>> are no longer in use on the backend side. This avoids starvation in >>>> case there are lots of persistent grants for a device which no longer >>>> is involved in I/O business. >>>> >>>> Signed-off-by: Juergen Gross >>>> --- >>>> drivers/block/xen-blkfront.c | 99 ++++++++++++++++++++++++++++++++++++++++++-- >>>> 1 file changed, 95 insertions(+), 4 deletions(-) >>>> >>>> diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c >>>> index b5cedccb5d7d..19feb8835fc4 100644 >>>> --- a/drivers/block/xen-blkfront.c >>>> +++ b/drivers/block/xen-blkfront.c >>>> @@ -46,6 +46,7 @@ >>>> #include >>>> #include >>>> #include >>>> +#include >>>> >>>> #include >>>> #include >>>> @@ -121,6 +122,9 @@ static inline struct blkif_req *blkif_req(struct request *rq) >>>> >>>> static DEFINE_MUTEX(blkfront_mutex); >>>> static const struct block_device_operations xlvbd_block_fops; >>>> +static struct delayed_work blkfront_work; >>>> +static LIST_HEAD(info_list); >>>> +static bool blkfront_work_active; >>>> >>>> /* >>>> * Maximum number of segments in indirect requests, the actual value used by >>>> @@ -216,6 +220,7 @@ struct blkfront_info >>>> /* Save uncomplete reqs and bios for migration. */ >>>> struct list_head requests; >>>> struct bio_list bio_list; >>>> + struct list_head info_list; >>>> }; >>>> >>>> static unsigned int nr_minors; >>>> @@ -1764,6 +1769,12 @@ static int write_per_ring_nodes(struct xenbus_transaction xbt, >>>> return err; >>>> } >>>> >>>> +static void free_info(struct blkfront_info *info) >>>> +{ >>>> + list_del(&info->info_list); >>>> + kfree(info); >>>> +} >>>> + >>>> /* Common code used when first setting up, and when resuming. */ >>>> static int talk_to_blkback(struct xenbus_device *dev, >>>> struct blkfront_info *info) >>>> @@ -1885,7 +1896,10 @@ static int talk_to_blkback(struct xenbus_device *dev, >>>> destroy_blkring: >>>> blkif_free(info, 0); >>>> >>>> - kfree(info); >>>> + mutex_lock(&blkfront_mutex); >>>> + free_info(info); >>>> + mutex_unlock(&blkfront_mutex); >>>> + >>>> dev_set_drvdata(&dev->dev, NULL); >>>> >>>> return err; >>>> @@ -1996,6 +2010,10 @@ static int blkfront_probe(struct xenbus_device *dev, >>>> info->handle = simple_strtoul(strrchr(dev->nodename, '/')+1, NULL, 0); >>>> dev_set_drvdata(&dev->dev, info); >>>> >>>> + mutex_lock(&blkfront_mutex); >>>> + list_add(&info->info_list, &info_list); >>>> + mutex_unlock(&blkfront_mutex); >>>> + >>>> return 0; >>>> } >>>> >>>> @@ -2306,6 +2324,15 @@ static void blkfront_gather_backend_features(struct blkfront_info *info) >>>> if (indirect_segments <= BLKIF_MAX_SEGMENTS_PER_REQUEST) >>>> indirect_segments = 0; >>>> info->max_indirect_segments = indirect_segments; >>>> + >>>> + if (info->feature_persistent) { >>>> + mutex_lock(&blkfront_mutex); >>>> + if (!blkfront_work_active) { >>>> + blkfront_work_active = true; >>>> + schedule_delayed_work(&blkfront_work, HZ * 10); >>> >>> Does it make sense to provide a module parameter to rune the schedule >>> of the cleanup routine? >> >> I don't think this is something anyone would like to tune. >> >> In case you think it should be tunable I can add a parameter, of course. > > We can always add it later if required. I'm fine as-is now. > >>> >>>> + } >>>> + mutex_unlock(&blkfront_mutex); >>> >>> Is it really necessary to have the blkfront_work_active boolean? What >>> happens if you queue the same delayed work more than once? >> >> In case there is already work queued later calls of >> schedule_delayed_work() will be ignored. >> >> So yes, I can drop the global boolean (I still need a local flag in >> blkfront_delay_work() for controlling the need to call >> schedule_delayed_work() again). > > Can't you just call schedule_delayed_work if info->feature_persistent > is set, even if that means calling it multiple times if multiple > blkfront instances are using persistent grants? I don't like that. With mq we have a high chance for multiple instances to use persistent grants and a local bool is much cheaper than unneeded calls of schedule_delayed_work(). Juergen