Re: [PATCH v4 1/1] Create debugfs file with virtio balloon usage information

[Alexander Atanasov <alexander.atanasov@virtuozzo.com>]

Hello,

On 05/07/2022 11:59, Michael S. Tsirkin wrote:
> On Tue, Jul 05, 2022 at 08:36:37AM +0000, Alexander Atanasov wrote:
>> Allow the guest to know how much it is ballooned by the host.
>> It is useful when debugging out of memory conditions.
>>
>> When host gets back memory from the guest it is accounted
>> as used memory in the guest but the guest have no way to know
>> how much it is actually ballooned.
>>
>> Signed-off-by: Alexander Atanasov <alexander.atanasov@virtuozzo.com>
>> ---
>>   drivers/virtio/virtio_balloon.c     | 77 +++++++++++++++++++++++++++++
>>   include/uapi/linux/virtio_balloon.h |  1 +
>>   2 files changed, 78 insertions(+)
>>
>> V2:
>>   - fixed coding style
>>   - removed pretty print
>> V3:
>>   - removed dublicate of features
>>   - comment about balooned_pages more clear
>>   - convert host pages to balloon pages
>> V4:
>>   - added a define for BALLOON_PAGE_SIZE to make things clear
>>
>> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
>> index b9737da6c4dd..dc4ad584b947 100644
>> --- a/drivers/virtio/virtio_balloon.c
>> +++ b/drivers/virtio/virtio_balloon.c
>> @@ -10,6 +10,7 @@
>>   #include <linux/virtio_balloon.h>
>>   #include <linux/swap.h>
>>   #include <linux/workqueue.h>
>> +#include <linux/debugfs.h>
>>   #include <linux/delay.h>
>>   #include <linux/slab.h>
>>   #include <linux/module.h>
>> @@ -731,6 +732,77 @@ static void report_free_page_func(struct work_struct *work)
>>   	}
>>   }
>>   
>> +/*
>> + * DEBUGFS Interface
>> + */
>> +#ifdef CONFIG_DEBUG_FS
>> +
>> +#define guest_to_balloon_pages(i) ((i)*VIRTIO_BALLOON_PAGES_PER_PAGE)
>> +/**
>> + * virtio_balloon_debug_show - shows statistics of balloon operations.
>> + * @f: pointer to the &struct seq_file.
>> + * @offset: ignored.
>> + *
>> + * Provides the statistics that can be accessed in virtio-balloon in the debugfs.
>> + *
>> + * Return: zero on success or an error code.
>> + */
>> +
>> +static int virtio_balloon_debug_show(struct seq_file *f, void *offset)
>> +{
>> +	struct virtio_balloon *b = f->private;
>> +	u32 num_pages;
>> +	struct sysinfo i;
>> +
>> +	si_meminfo(&i);
>> +
>> +	seq_printf(f, "%-22s: %d\n", "page_size", VIRTIO_BALLOON_PAGE_SIZE);
>> +
>> +	virtio_cread_le(b->vdev, struct virtio_balloon_config, actual,
>> +			&num_pages);
>> +	/*
>> +	 * Pages allocated by host from the guest memory.
>> +	 * Host inflates the balloon to get more memory.
>> +	 * Guest needs to deflate the balloon to get more memory.
>> +	 */
>> +	seq_printf(f, "%-22s: %u\n", "ballooned_pages", num_pages);
>> +
>> +	/* Total Memory for the guest from host */
>> +	seq_printf(f, "%-22s: %lu\n", "total_pages",
>> +			guest_to_balloon_pages(i.totalram));
>> +
>> +	/* Current memory for the guest */
>> +	seq_printf(f, "%-22s: %lu\n", "current_pages",
>> +			guest_to_balloon_pages(i.totalram) - num_pages);
>> +
>> +	return 0;
>> +}
>> +
>> +DEFINE_SHOW_ATTRIBUTE(virtio_balloon_debug);
>> +
>> +static void  virtio_balloon_debugfs_init(struct virtio_balloon *b)
>> +{
>> +	debugfs_create_file("virtio-balloon", 0444, NULL, b,
>> +			    &virtio_balloon_debug_fops);
>> +}
>> +
>> +static void  virtio_balloon_debugfs_exit(struct virtio_balloon *b)
>> +{
>> +	debugfs_remove(debugfs_lookup("virtio-balloon", NULL));
>> +}
>> +
>> +#else
>> +
>> +static inline void virtio_balloon_debugfs_init(struct virtio_balloon *b)
>> +{
>> +}
>> +
>> +static inline void virtio_balloon_debugfs_exit(struct virtio_balloon *b)
>> +{
>> +}
>> +
>> +#endif	/* CONFIG_DEBUG_FS */
>> +
>>   #ifdef CONFIG_BALLOON_COMPACTION
>>   /*
>>    * virtballoon_migratepage - perform the balloon page migration on behalf of
>> @@ -1019,6 +1091,9 @@ static int virtballoon_probe(struct virtio_device *vdev)
>>   
>>   	if (towards_target(vb))
>>   		virtballoon_changed(vdev);
>> +
>> +	virtio_balloon_debugfs_init(vb);
>> +
>>   	return 0;
>>   
>>   out_unregister_oom:
>> @@ -1065,6 +1140,8 @@ static void virtballoon_remove(struct virtio_device *vdev)
>>   {
>>   	struct virtio_balloon *vb = vdev->priv;
>>   
>> +	virtio_balloon_debugfs_exit(vb);
>> +
>>   	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_REPORTING))
>>   		page_reporting_unregister(&vb->pr_dev_info);
>>   	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_DEFLATE_ON_OOM))
>> diff --git a/include/uapi/linux/virtio_balloon.h b/include/uapi/linux/virtio_balloon.h
>> index ddaa45e723c4..f3ff7c4e5884 100644
>> --- a/include/uapi/linux/virtio_balloon.h
>> +++ b/include/uapi/linux/virtio_balloon.h
>> @@ -40,6 +40,7 @@
>>   
>>   /* Size of a PFN in the balloon interface. */
>>   #define VIRTIO_BALLOON_PFN_SHIFT 12
>> +#define VIRTIO_BALLOON_PAGE_SIZE (1<<VIRTIO_BALLOON_PFN_SHIFT)
>>   #define VIRTIO_BALLOON_CMD_ID_STOP	0
>>   #define VIRTIO_BALLOON_CMD_ID_DONE	1
> Did you run checkpatch on this?


Sure, i did:

scripts/checkpatch.pl 
../outgoing/v4-0001-Create-debugfs-file-with-virtio-balloon-usage-inf.patch
total: 0 errors, 0 warnings, 108 lines checked

../outgoing/v4-0001-Create-debugfs-file-with-virtio-balloon-usage-inf.patch 
has no obvious style problems and is ready for submission.

-- 
Regards,
Alexander Atanasov