RE: [PATCH v2 1/1] Create debugfs file with hyper-v balloon usage information

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From: Alexander Atanasov <alexander.atanasov@xxxxxxxxxxxxx> Sent: Wednesday, July 6, 2022 11:15 AM
> 
> 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.
> 
> Expose current state, flags and max possible memory to the guest.
> While at it - fix a 10+ years old typo.
> 
> Signed-off-by: Alexander Atanasov <alexander.atanasov@xxxxxxxxxxxxx>
> ---
>  drivers/hv/hv_balloon.c | 126 +++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 125 insertions(+), 1 deletion(-)
> 
> V1->V2:
>  - Fix C&P errors - you got me :)

Did you see my code comments on v1 of your patch (in addition to my
broader comment about debugfs vs. tracing) ?  I didn't see a response from
you, and my code suggestions are not incorporated into this v2, so I wondered
if you disagreed with my suggestions, or just missed them.

Michael

> 
> Note - no attempt to handle guest vs host page size difference
> is made - see ballooning_enabled.
> Basicly if balloon page size != guest page size balloon is off.
> 
> diff --git a/drivers/hv/hv_balloon.c b/drivers/hv/hv_balloon.c
> index 91e8a72eee14..91dfde06c6fb 100644
> --- a/drivers/hv/hv_balloon.c
> +++ b/drivers/hv/hv_balloon.c
> @@ -11,6 +11,7 @@
>  #include <linux/kernel.h>
>  #include <linux/jiffies.h>
>  #include <linux/mman.h>
> +#include <linux/debugfs.h>
>  #include <linux/delay.h>
>  #include <linux/init.h>
>  #include <linux/module.h>
> @@ -248,7 +249,7 @@ struct dm_capabilities_resp_msg {
>   * num_committed: Committed memory in pages.
>   * page_file_size: The accumulated size of all page files
>   *                in the system in pages.
> - * zero_free: The nunber of zero and free pages.
> + * zero_free: The number of zero and free pages.
>   * page_file_writes: The writes to the page file in pages.
>   * io_diff: An indicator of file cache efficiency or page file activity,
>   *         calculated as File Cache Page Fault Count - Page Read Count.
> @@ -567,6 +568,13 @@ struct hv_dynmem_device {
>         __u32 version;
> 
>         struct page_reporting_dev_info pr_dev_info;
> +
> +#ifdef CONFIG_DEBUG_FS
> +       /*
> +        * Maximum number of pages that can be hot_add-ed
> +        */
> +       __u64 max_dynamic_page_count;
> +#endif
>  };
> 
>  static struct hv_dynmem_device dm_device;
> @@ -1078,6 +1086,9 @@ static void process_info(struct hv_dynmem_device *dm,
> struct dm_info_msg *msg)
> 
>                         pr_info("Max. dynamic memory size: %llu MB\n",
>                                 (*max_page_count) >> (20 - HV_HYP_PAGE_SHIFT));
> +#ifdef CONFIG_DEBUG_FS
> +                       dm->max_dynamic_page_count = *max_page_count;
> +#endif
>                 }
> 
>                 break;
> @@ -1807,6 +1818,115 @@ static int balloon_connect_vsp(struct hv_device *dev)
>         return ret;
>  }
> 
> +/*
> + * DEBUGFS Interface
> + */
> +#ifdef CONFIG_DEBUG_FS
> +
> +/**
> + * hv_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 hv-balloon in the debugfs.
> + *
> + * Return: zero on success or an error code.
> + */
> +static int hv_balloon_debug_show(struct seq_file *f, void *offset)
> +{
> +       struct hv_dynmem_device *dm = f->private;
> +       unsigned long num_pages_committed;
> +       char *sname;
> +
> +       seq_printf(f, "%-22s: %u.%u\n", "host_version",
> +                               DYNMEM_MAJOR_VERSION(dm->version),
> +                               DYNMEM_MINOR_VERSION(dm->version));
> +
> +       seq_printf(f, "%-22s:", "capabilities");
> +       if (ballooning_enabled())
> +               seq_puts(f, " enabled");
> +
> +       if (hot_add_enabled())
> +               seq_puts(f, " hot_add");
> +
> +       seq_puts(f, "\n");
> +
> +       seq_printf(f, "%-22s: %u", "state", dm->state);
> +       switch (dm->state) {
> +       case DM_INITIALIZING:
> +                       sname = "Initializing";
> +                       break;
> +       case DM_INITIALIZED:
> +                       sname = "Initialized";
> +                       break;
> +       case DM_BALLOON_UP:
> +                       sname = "Balloon Up";
> +                       break;
> +       case DM_BALLOON_DOWN:
> +                       sname = "Balloon Down";
> +                       break;
> +       case DM_HOT_ADD:
> +                       sname = "Hot Add";
> +                       break;
> +       case DM_INIT_ERROR:
> +                       sname = "Error";
> +                       break;
> +       default:
> +                       sname = "Unknown";
> +       }
> +       seq_printf(f, " (%s)\n", sname);
> +
> +       /* HV Page Size */
> +       seq_printf(f, "%-22s: %ld\n", "page_size", HV_HYP_PAGE_SIZE);
> +
> +       /* Pages added with hot_add */
> +       seq_printf(f, "%-22s: %u\n", "pages_added", dm->num_pages_added);
> +
> +       /* pages that are "onlined"/used from pages_added */
> +       seq_printf(f, "%-22s: %u\n", "pages_onlined", dm->num_pages_onlined);
> +
> +       /* pages we have given back to host */
> +       seq_printf(f, "%-22s: %u\n", "pages_ballooned", dm->num_pages_ballooned);
> +
> +       num_pages_committed = vm_memory_committed();
> +       num_pages_committed += dm->num_pages_ballooned +
> +                               (dm->num_pages_added > dm->num_pages_onlined ?
> +                               dm->num_pages_added - dm->num_pages_onlined : 0) +
> +                               compute_balloon_floor();
> +       seq_printf(f, "%-22s: %lu\n", "total_pages_commited",
> +                               num_pages_committed);
> +
> +       seq_printf(f, "%-22s: %llu\n", "max_dynamic_page_count",
> +                               dm->max_dynamic_page_count);
> +
> +       return 0;
> +}
> +
> +DEFINE_SHOW_ATTRIBUTE(hv_balloon_debug);
> +
> +static void  hv_balloon_debugfs_init(struct hv_dynmem_device *b)
> +{
> +       debugfs_create_file("hv-balloon", 0444, NULL, b,
> +                       &hv_balloon_debug_fops);
> +}
> +
> +static void  hv_balloon_debugfs_exit(struct hv_dynmem_device *b)
> +{
> +       debugfs_remove(debugfs_lookup("hv-balloon", NULL));
> +}
> +
> +#else
> +
> +static inline void hv_balloon_debugfs_init(struct hv_dynmem_device  *b)
> +{
> +}
> +
> +static inline void hv_balloon_debugfs_exit(struct hv_dynmem_device *b)
> +{
> +}
> +
> +#endif /* CONFIG_DEBUG_FS */
> +
>  static int balloon_probe(struct hv_device *dev,
>                          const struct hv_vmbus_device_id *dev_id)
>  {
> @@ -1854,6 +1974,8 @@ static int balloon_probe(struct hv_device *dev,
>                 goto probe_error;
>         }
> 
> +       hv_balloon_debugfs_init(&dm_device);
> +
>         return 0;
> 
>  probe_error:
> @@ -1879,6 +2001,8 @@ static int balloon_remove(struct hv_device *dev)
>         if (dm->num_pages_ballooned != 0)
>                 pr_warn("Ballooned pages: %d\n", dm->num_pages_ballooned);
> 
> +       hv_balloon_debugfs_exit(dm);
> +
>         cancel_work_sync(&dm->balloon_wrk.wrk);
>         cancel_work_sync(&dm->ha_wrk.wrk);
> 
> --
> 2.25.1





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