linux-kernel - Re: [PATCH v8 03/12] mm/sparsemem: Add helpers track active portions of a section at boot

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Date:   Fri, 10 May 2019 14:56:54 +0200
From:   osalvador@...e.de
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     akpm@...ux-foundation.org, Michal Hocko <mhocko@...e.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Logan Gunthorpe <logang@...tatee.com>,
        Pavel Tatashin <pasha.tatashin@...een.com>,
        Jane Chu <jane.chu@...cle.com>, linux-nvdimm@...ts.01.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 03/12] mm/sparsemem: Add helpers track active portions
 of a section at boot

On 2019-05-07 01:39, Dan Williams wrote:
> Prepare for hot{plug,remove} of sub-ranges of a section by tracking a
> sub-section active bitmask, each bit representing a PMD_SIZE span of 
> the
> architecture's memory hotplug section size.
> 
> The implications of a partially populated section is that pfn_valid()
> needs to go beyond a valid_section() check and read the sub-section
> active ranges from the bitmask. The expectation is that the bitmask
> (subsection_map) fits in the same cacheline as the valid_section() 
> data,
> so the incremental performance overhead to pfn_valid() should be
> negligible.
> 
> Cc: Michal Hocko <mhocko@...e.com>
> Cc: Vlastimil Babka <vbabka@...e.cz>
> Cc: Logan Gunthorpe <logang@...tatee.com>
> Cc: Oscar Salvador <osalvador@...e.de>
> Cc: Pavel Tatashin <pasha.tatashin@...een.com>
> Tested-by: Jane Chu <jane.chu@...cle.com>
> Signed-off-by: Dan Williams <dan.j.williams@...el.com>

Now that the handling is done in pfn/nr_pages, it looks better to me:

Reviewed-by: Oscar Salvador <osalvador@...e.de>

Thanks