Re: [PATCH v1 1/2] Enable balloon drivers to report inflated memory

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Aug 09, 2022 at 12:49:32PM +0300, Alexander Atanasov wrote:
> Display reported in /proc/meminfo as:
> 
> Inflated(total) or Inflated(free)
> 
> depending on the driver.
> 
> Drivers use the sign bit to indicate where they do account
> the inflated memory.
> 
> Amount of inflated memory can be used by:
>  - as a hint for the oom a killer
>  - user space software that monitors memory pressure
> 
> Cc: David Hildenbrand <david@redhat.com>
> Cc: Wei Liu <wei.liu@kernel.org>
> Cc: Nadav Amit <namit@vmware.com>
> 
> Signed-off-by: Alexander Atanasov <alexander.atanasov@virtuozzo.com>
> ---
>  Documentation/filesystems/proc.rst |  5 +++++
>  fs/proc/meminfo.c                  | 11 +++++++++++
>  include/linux/mm.h                 |  4 ++++
>  mm/page_alloc.c                    |  4 ++++
>  4 files changed, 24 insertions(+)
> 
> diff --git a/Documentation/filesystems/proc.rst b/Documentation/filesystems/proc.rst
> index 1bc91fb8c321..064b5b3d5bd8 100644
> --- a/Documentation/filesystems/proc.rst
> +++ b/Documentation/filesystems/proc.rst
> @@ -986,6 +986,7 @@ Example output. You may not have all of these fields.
>      VmallocUsed:       40444 kB
>      VmallocChunk:          0 kB
>      Percpu:            29312 kB
> +    Inflated(total):  2097152 kB
>      HardwareCorrupted:     0 kB
>      AnonHugePages:   4149248 kB
>      ShmemHugePages:        0 kB
> @@ -1133,6 +1134,10 @@ VmallocChunk
>  Percpu
>                Memory allocated to the percpu allocator used to back percpu
>                allocations. This stat excludes the cost of metadata.
> +Inflated(total) or Inflated(free)
> +               Amount of memory that is inflated by the balloon driver.
> +               Due to differences among balloon drivers inflated memory
> +               is either subtracted from TotalRam or from MemFree.
>  HardwareCorrupted
>                The amount of RAM/memory in KB, the kernel identifies as
>                corrupted.
> diff --git a/fs/proc/meminfo.c b/fs/proc/meminfo.c
> index 6e89f0e2fd20..ebbe52ccbb93 100644
> --- a/fs/proc/meminfo.c
> +++ b/fs/proc/meminfo.c
> @@ -38,6 +38,9 @@ static int meminfo_proc_show(struct seq_file *m, void *v)
>  	unsigned long pages[NR_LRU_LISTS];
>  	unsigned long sreclaimable, sunreclaim;
>  	int lru;
> +#ifdef CONFIG_MEMORY_BALLOON
> +	long inflated_kb;
> +#endif
>  
>  	si_meminfo(&i);
>  	si_swapinfo(&i);
> @@ -153,6 +156,14 @@ static int meminfo_proc_show(struct seq_file *m, void *v)
>  		    global_zone_page_state(NR_FREE_CMA_PAGES));
>  #endif
>  
> +#ifdef CONFIG_MEMORY_BALLOON
> +	inflated_kb = atomic_long_read(&mem_balloon_inflated_kb);
> +	if (inflated_kb >= 0)
> +		seq_printf(m,  "Inflated(total): %8ld kB\n", inflated_kb);
> +	else
> +		seq_printf(m,  "Inflated(free): %8ld kB\n", -inflated_kb);
> +#endif
> +
>  	hugetlb_report_meminfo(m);
>  
>  	arch_report_meminfo(m);


This seems too baroque for my taste.
Why not just have two counters for the two pruposes?
And is there any value in having this atomic?
We want a consistent value but just READ_ONCE seems sufficient ...


> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 7898e29bcfb5..b190811dc16e 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -2582,6 +2582,10 @@ extern int watermark_boost_factor;
>  extern int watermark_scale_factor;
>  extern bool arch_has_descending_max_zone_pfns(void);
>  
> +#ifdef CONFIG_MEMORY_BALLOON
> +extern atomic_long_t mem_balloon_inflated_kb;
> +#endif
> +
>  /* nommu.c */
>  extern atomic_long_t mmap_pages_allocated;
>  extern int nommu_shrink_inode_mappings(struct inode *, size_t, size_t);
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index b0bcab50f0a3..12359179a3a2 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -194,6 +194,10 @@ EXPORT_SYMBOL(init_on_alloc);
>  DEFINE_STATIC_KEY_MAYBE(CONFIG_INIT_ON_FREE_DEFAULT_ON, init_on_free);
>  EXPORT_SYMBOL(init_on_free);
>  
> +#ifdef CONFIG_MEMORY_BALLOON
> +atomic_long_t mem_balloon_inflated_kb = ATOMIC_LONG_INIT(0);
> +#endif
> +
>  static bool _init_on_alloc_enabled_early __read_mostly
>  				= IS_ENABLED(CONFIG_INIT_ON_ALLOC_DEFAULT_ON);
>  static int __init early_init_on_alloc(char *buf)
> -- 
> 2.31.1
> 
>