linux-kernel - Re: [PATCH v4 3/4] mm/sparse: Add a new parameter 'data_unit_size' for alloc_usemap_and

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Message-ID: <20180608062733.GB16231@MiWiFi-R3L-srv>
Date:   Fri, 8 Jun 2018 14:27:33 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
        pagupta@...hat.com, linux-mm@...ck.org,
        kirill.shutemov@...ux.intel.com
Subject: Re: [PATCH v4 3/4] mm/sparse: Add a new parameter 'data_unit_size'
 for alloc_usemap_and_memmap

On 06/07/18 at 03:48pm, Dave Hansen wrote:
> 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?

Thanks for reviewing, Dave.

In alloc_usemap_and_memmap(), it will call
sparse_early_usemaps_alloc_node() or sparse_early_mem_maps_alloc_node()
to allocate usemap and memmap for each node and install them into
usemap_map[] and map_map[]. Here we need pass in the number of present
sections on this node so that we can move pointer of usemap_map[] and
map_map[] to right position.

How do think about above words?

Thanks
Baoquan