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Date: Thu, 18 Apr 2024 13:49:46 +0200
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Subject: Re: [PATCH 2/3] virtio_balloon: introduce memory allocation stall
 counter
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: <20240418062602.1291391-1-pizhenwei@bytedance.com>
 <20240418062602.1291391-3-pizhenwei@bytedance.com>
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From: David Hildenbrand <david@redhat.com>
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Organization: Red Hat
In-Reply-To: <20240418062602.1291391-3-pizhenwei@bytedance.com>
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On 18.04.24 08:26, zhenwei pi wrote:
> Memory allocation stall counter represents the performance/latency of
> memory allocation, expose this counter to the host side by virtio
> balloon device via out-of-bound way.
> 
> Signed-off-by: zhenwei pi <pizhenwei@bytedance.com>
> ---
>   drivers/virtio/virtio_balloon.c     | 20 +++++++++++++++++++-
>   include/uapi/linux/virtio_balloon.h |  6 ++++--
>   2 files changed, 23 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> index fd19934a847f..e88e6573afa5 100644
> --- a/drivers/virtio/virtio_balloon.c
> +++ b/drivers/virtio/virtio_balloon.c
> @@ -321,7 +321,7 @@ static unsigned int update_balloon_stats(struct virtio_balloon *vb)
>   	unsigned long events[NR_VM_EVENT_ITEMS];
>   	struct sysinfo i;
>   	unsigned int idx = 0;
> -	long available;
> +	long available, stall = 0;
>   	unsigned long caches;
>   
>   	all_vm_events(events);
> @@ -338,6 +338,24 @@ static unsigned int update_balloon_stats(struct virtio_balloon *vb)
>   	update_stat(vb, idx++, VIRTIO_BALLOON_S_MAJFLT, events[PGMAJFAULT]);
>   	update_stat(vb, idx++, VIRTIO_BALLOON_S_MINFLT, events[PGFAULT]);
>   	update_stat(vb, idx++, VIRTIO_BALLOON_S_OOM_KILL, events[OOM_KILL]);
> +
> +	/* sum all the stall events */
> +#ifdef CONFIG_ZONE_DMA
> +	stall += events[ALLOCSTALL_DMA];
> +#endif
> +#ifdef CONFIG_ZONE_DMA32
> +	stall += events[ALLOCSTALL_DMA32];
> +#endif
> +#ifdef CONFIG_HIGHMEM
> +	stall += events[ALLOCSTALL_HIGH];
> +#endif
> +#ifdef CONFIG_ZONE_DEVICE
> +	stall += events[ALLOCSTALL_DEVICE];
> +#endif

Naive me would think that ALLOCSTALL_DEVICE is always 0. :)

Likely we should just do:

for (zid = 0; zid < MAX_NR_ZONES; zid++)
	stall += events[ALLOCSTALL_NORMAL - ZONE_NORMAL + zid];

(see isolate_lru_folios() -> __count_zid_vm_events(), where we realy on 
the same ordering)

Apart form that, LGTM.

-- 
Cheers,

David / dhildenb