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Subject: Re: [PATCH RESEND] mm: show number of vmalloc pages in /proc/meminfo
To:     Roman Gushchin <guro@fb.com>,
        Andrew Morton <akpm@linux-foundation.org>
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        kernel-team@fb.com, Johannes Weiner <hannes@cmpxchg.org>
References: <20190514235111.2817276-1-guro@fb.com>
 <20190514235111.2817276-2-guro@fb.com>
From:   Anshuman Khandual <anshuman.khandual@arm.com>
Message-ID: <f0e640c9-2eff-ffc5-8558-4bc1b374eb2a@arm.com>
Date:   Wed, 15 May 2019 12:44:16 +0530
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On 05/15/2019 05:21 AM, Roman Gushchin wrote:
> Vmalloc() is getting more and more used these days (kernel stacks,
> bpf and percpu allocator are new top users), and the total %
> of memory consumed by vmalloc() can be pretty significant
> and changes dynamically.
> 
> /proc/meminfo is the best place to display this information:
> its top goal is to show top consumers of the memory.
> 
> Since the VmallocUsed field in /proc/meminfo is not in use
> for quite a long time (it has been defined to 0 by the
> commit a5ad88ce8c7f ("mm: get rid of 'vmalloc_info' from
> /proc/meminfo")), let's reuse it for showing the actual
> physical memory consumption of vmalloc().
The primary concern which got addressed with a5ad88ce8c7f was that computing
get_vmalloc_info() was taking long time. But here its reads an already updated
value which gets added or subtracted during __vmalloc_area_node/__vunmap cycle.
Hence this should not cost much (like get_vmalloc_info). But is not this similar
to the caching solution Linus mentioned.