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Message-ID: <67c0bbac-aa4a-28ce-5416-e41af794e899@redhat.com>
Date:   Mon, 18 Sep 2023 13:28:06 +0200
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Subject: Re: [PATCH v1 2/4] mm/ksm: add pages_skipped metric
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To:     Stefan Roesch <shr@devkernel.io>, kernel-team@fb.com
Cc:     akpm@linux-foundation.org, hannes@cmpxchg.org, riel@surriel.com,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org
References: <20230912175228.952039-1-shr@devkernel.io>
 <20230912175228.952039-3-shr@devkernel.io>
From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat
In-Reply-To: <20230912175228.952039-3-shr@devkernel.io>
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On 12.09.23 19:52, Stefan Roesch wrote:
> This change adds the "pages skipped" metric. To be able to evaluate how
> successful smart page scanning is, the pages skipped metric can be
> compared to the pages scanned metric.
> 
> The pages skipped metric is a cumulative counter. The counter is stored
> under /sys/kernel/mm/ksm/pages_skipped.
> 
> Signed-off-by: Stefan Roesch <shr@devkernel.io>
> ---
>   mm/ksm.c | 12 ++++++++++++
>   1 file changed, 12 insertions(+)
> 
> diff --git a/mm/ksm.c b/mm/ksm.c
> index bfd5087c7d5a..728574a3033e 100644
> --- a/mm/ksm.c
> +++ b/mm/ksm.c
> @@ -293,6 +293,9 @@ static bool ksm_smart_scan;
>   /* The number of zero pages which is placed by KSM */
>   unsigned long ksm_zero_pages;
>   
> +/* The number of pages that have been skipped due to "smart scanning" */
> +static unsigned long ksm_pages_skipped;
> +
>   #ifdef CONFIG_NUMA
>   /* Zeroed when merging across nodes is not allowed */
>   static unsigned int ksm_merge_across_nodes = 1;
> @@ -2345,6 +2348,7 @@ static bool skip_rmap_item(struct page *page, struct ksm_rmap_item *rmap_item)
>   		return false;
>   	}
>   
> +	ksm_pages_skipped++;
>   	if (rmap_item->skip_age == 0) {
>   		rmap_item->skip_age = age + inc_skip_age(age);
>   		remove_rmap_item_from_tree(rmap_item);
> @@ -3435,6 +3439,13 @@ static ssize_t pages_volatile_show(struct kobject *kobj,
>   }
>   KSM_ATTR_RO(pages_volatile);
>   
> +static ssize_t pages_skipped_show(struct kobject *kobj,
> +				  struct kobj_attribute *attr, char *buf)
> +{
> +	return sysfs_emit(buf, "%lu\n", ksm_pages_skipped);
> +}
> +KSM_ATTR_RO(pages_skipped);
> +
>   static ssize_t ksm_zero_pages_show(struct kobject *kobj,
>   				struct kobj_attribute *attr, char *buf)
>   {
> @@ -3532,6 +3543,7 @@ static struct attribute *ksm_attrs[] = {
>   	&pages_sharing_attr.attr,
>   	&pages_unshared_attr.attr,
>   	&pages_volatile_attr.attr,
> +	&pages_skipped_attr.attr,
>   	&ksm_zero_pages_attr.attr,
>   	&full_scans_attr.attr,
>   #ifdef CONFIG_NUMA

Reviewed-by: David Hildenbrand <david@redhat.com>

-- 
Cheers,

David / dhildenb