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Subject: Re: [PATCH] mm: add ZONE_DEVICE statistics to smaps
To: Dan Williams <dan.j.williams@intel.com>, akpm@linux-foundation.org
References: <147881591739.39198.1358237993213024627.stgit@dwillia2-desk3.amr.corp.intel.com>
Cc: linux-nvdimm@ml01.01.org, Christoph Hellwig <hch@lst.de>,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org
From: Dave Hansen <dave.hansen@intel.com>
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Date: Tue, 15 Nov 2016 16:15:05 -0800
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On 11/10/2016 02:11 PM, Dan Williams wrote:
> @@ -774,6 +778,8 @@ static int show_smap(struct seq_file *m, void *v, int is_pid)
>  		   "ShmemPmdMapped: %8lu kB\n"
>  		   "Shared_Hugetlb: %8lu kB\n"
>  		   "Private_Hugetlb: %7lu kB\n"
> +		   "Device:         %8lu kB\n"
> +		   "DeviceHugePages: %7lu kB\n"
>  		   "Swap:           %8lu kB\n"
>  		   "SwapPss:        %8lu kB\n"
>  		   "KernelPageSize: %8lu kB\n"

So, a couple of nits...

smaps is getting a bit big, and the fields that get added in this patch
are going to be pretty infrequently used.  Is it OK if smaps grows
forever, even if most of them items are "0 kB"?

IOW, Could we make it output Device* only for DAX VMAs?  All the parsers
have to handle that field being there or not (for old kernels).

The other thing missing for DAX is the page size.  DAX mappings support
mixed page sizes, so MMUPageSize in this context is pretty worthless.
What will we do in here for 1GB DAX pages?