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Subject: Re: [PATCH v4 3/4] mm/sparse: Add a new parameter 'data_unit_size'
 for alloc_usemap_and_memmap
References: <20180521101555.25610-1-bhe@redhat.com>
 <20180521101555.25610-4-bhe@redhat.com>
From: Dave Hansen <dave.hansen@intel.com>
Message-ID: <8ff7638c-d3ee-a40c-e5cf-deded8d19e93@intel.com>
Date: Thu, 7 Jun 2018 15:48:07 -0700
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To: Baoquan He <bhe@redhat.com>, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, pagupta@redhat.com
Cc: linux-mm@kvack.org, kirill.shutemov@linux.intel.com

On 05/21/2018 03:15 AM, Baoquan He wrote:
> It's used to pass the size of map data unit into alloc_usemap_and_memmap,
> and is preparation for next patch.

This is the "what", but not the "why".  Could you add another sentence
or two to explain why we need this?