linux-kernel - Re: [PATCH v2] memcg: add per-memcg vmalloc stat

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Date:   Mon, 27 Dec 2021 11:48:35 +0100
From:   Michal Hocko <mhocko@...e.com>
To:     Shakeel Butt <shakeelb@...gle.com>
Cc:     Johannes Weiner <hannes@...xchg.org>, Roman Gushchin <guro@...com>,
        Muchun Song <songmuchun@...edance.com>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] memcg: add per-memcg vmalloc stat

On Tue 21-12-21 21:24:57, Shakeel Butt wrote:
> The kvmalloc* allocation functions can fallback to vmalloc allocations
> and more often on long running machines. In addition the kernel does
> have __GFP_ACCOUNT kvmalloc* calls. So, often on long running machines,
> the memory.stat does not tell the complete picture which type of memory
> is charged to the memcg. So add a per-memcg vmalloc stat.
> 
> Signed-off-by: Shakeel Butt <shakeelb@...gle.com>

The counter is useful IMHO. I just have one implementation specific
question.
[...]
> @@ -2626,6 +2627,9 @@ static void __vunmap(const void *addr, int deallocate_pages)
>  		unsigned int page_order = vm_area_page_order(area);
>  		int i;
>  
> +		mod_memcg_page_state(area->pages[0], MEMCG_VMALLOC,
> +				     -(int)area->nr_pages);
> +
>  		for (i = 0; i < area->nr_pages; i += 1U << page_order) {
>  			struct page *page = area->pages[i];
>  
> @@ -2964,6 +2968,7 @@ static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,
>  		page_order, nr_small_pages, area->pages);
>  
>  	atomic_long_add(area->nr_pages, &nr_vmalloc_pages);
> +	mod_memcg_page_state(area->pages[0], MEMCG_VMALLOC, area->nr_pages);
>  
>  	/*
>  	 * If not enough pages were obtained to accomplish an

Is it safe to assume that the whole area is always charged to the same
memcg? I am not really deeply familiar with vmalloc internals but is it
possible that an area could get resized/partially reused with a
different charging context?

A clarification comment would be really handy.
-- 
Michal Hocko
SUSE Labs