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Date: Mon, 22 Apr 2024 11:11:15 +0200
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Subject: Re: [PATCH v2 1/4] virtio_balloon: separate vm events into a function
To: zhenwei pi <pizhenwei@bytedance.com>, linux-kernel@vger.kernel.org,
 linux-mm@kvack.org, virtualization@lists.linux.dev
Cc: mst@redhat.com, jasowang@redhat.com, xuanzhuo@linux.alibaba.com,
 akpm@linux-foundation.org
References: <20240422074254.1440457-1-pizhenwei@bytedance.com>
 <20240422074254.1440457-2-pizhenwei@bytedance.com>
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From: David Hildenbrand <david@redhat.com>
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Organization: Red Hat
In-Reply-To: <20240422074254.1440457-2-pizhenwei@bytedance.com>
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On 22.04.24 09:42, zhenwei pi wrote:
> All the VM events related statistics have dependence on
> 'CONFIG_VM_EVENT_COUNTERS', once any stack variable is required by any
> VM events in future, we would have codes like:
>   #ifdef CONFIG_VM_EVENT_COUNTERS
>        unsigned long foo;
>   #endif
>        ...
>   #ifdef CONFIG_VM_EVENT_COUNTERS
>        foo = events[XXX] + events[YYY];
>        update_stat(vb, idx++, VIRTIO_BALLOON_S_XXX, foo);
>   #endif
> 
> Separate vm events into a single function, also remove
> 'CONFIG_VM_EVENT_COUNTERS' from 'update_balloon_stats'.
> 
> Signed-off-by: zhenwei pi <pizhenwei@bytedance.com>
> ---
>   drivers/virtio/virtio_balloon.c | 44 ++++++++++++++++++++++-----------
>   1 file changed, 29 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> index 1f5b3dd31fcf..59fe157e5722 100644
> --- a/drivers/virtio/virtio_balloon.c
> +++ b/drivers/virtio/virtio_balloon.c
> @@ -316,34 +316,48 @@ static inline void update_stat(struct virtio_balloon *vb, int idx,
>   
>   #define pages_to_bytes(x) ((u64)(x) << PAGE_SHIFT)
>   
> -static unsigned int update_balloon_stats(struct virtio_balloon *vb)
> +/* Return the number of entries filled by vm events */
> +static inline unsigned int update_balloon_vm_stats(struct virtio_balloon *vb,
> +						   unsigned int start)
>   {
> +#ifdef CONFIG_VM_EVENT_COUNTERS
>   	unsigned long events[NR_VM_EVENT_ITEMS];
> -	struct sysinfo i;
> -	unsigned int idx = 0;
> -	long available;
> -	unsigned long caches;
> +	unsigned int idx = start;
>   
>   	all_vm_events(events);
> -	si_meminfo(&i);
> -
> -	available = si_mem_available();
> -	caches = global_node_page_state(NR_FILE_PAGES);
> -
> -#ifdef CONFIG_VM_EVENT_COUNTERS
>   	update_stat(vb, idx++, VIRTIO_BALLOON_S_SWAP_IN,
> -				pages_to_bytes(events[PSWPIN]));
> +		    pages_to_bytes(events[PSWPIN]));
>   	update_stat(vb, idx++, VIRTIO_BALLOON_S_SWAP_OUT,
> -				pages_to_bytes(events[PSWPOUT]));
> +		    pages_to_bytes(events[PSWPOUT]));
>   	update_stat(vb, idx++, VIRTIO_BALLOON_S_MAJFLT, events[PGMAJFAULT]);
>   	update_stat(vb, idx++, VIRTIO_BALLOON_S_MINFLT, events[PGFAULT]);
> +
>   #ifdef CONFIG_HUGETLB_PAGE
>   	update_stat(vb, idx++, VIRTIO_BALLOON_S_HTLB_PGALLOC,
>   		    events[HTLB_BUDDY_PGALLOC]);
>   	update_stat(vb, idx++, VIRTIO_BALLOON_S_HTLB_PGFAIL,
>   		    events[HTLB_BUDDY_PGALLOC_FAIL]);
> -#endif
> -#endif
> +#endif /* CONFIG_HUGETLB_PAGE */
> +
> +	return idx - start;
> +#else /* CONFIG_VM_EVENT_COUNTERS */
> +
> +	return 0;
> +#endif /* CONFIG_VM_EVENT_COUNTERS */
> +}
> +
> +static unsigned int update_balloon_stats(struct virtio_balloon *vb)
> +{
> +	struct sysinfo i;
> +	unsigned int idx = 0;
> +	long available;
> +	unsigned long caches;
> +
> +	idx += update_balloon_vm_stats(vb, idx);

No need to handle idx that complicated now. Just do

unsigned int idx;

idx = update_balloon_vm_stats(vb);

We can go down that path if we ever want to rearrange the code and not 
have the vm_stats first.

> +
> +	si_meminfo(&i);
> +	available = si_mem_available();
> +	caches = global_node_page_state(NR_FILE_PAGES);
>   	update_stat(vb, idx++, VIRTIO_BALLOON_S_MEMFREE,
>   				pages_to_bytes(i.freeram));
>   	update_stat(vb, idx++, VIRTIO_BALLOON_S_MEMTOT,

-- 
Cheers,

David / dhildenb