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Date:   Wed, 5 Aug 2020 21:49:55 +0000
From:   Wei Yang <richard.weiyang@gmail.com>
To:     Wei Yang <richard.weiyang@linux.alibaba.com>
Cc:     akpm@linux-foundation.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, david@redhat.com
Subject: Re: [Patch v2] mm/sparse: only sub-section aligned range would be
 populated
Message-ID: <20200805214955.ds7y3nwjoz2ms37h@master>
Reply-To: Wei Yang <richard.weiyang@gmail.com>
References: <20200703031828.14645-1-richard.weiyang@linux.alibaba.com>
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On Fri, Jul 03, 2020 at 11:18:28AM +0800, Wei Yang wrote:
>There are two code path which invoke __populate_section_memmap()
>
>  * sparse_init_nid()
>  * sparse_add_section()
>
>For both case, we are sure the memory range is sub-section aligned.
>
>  * we pass PAGES_PER_SECTION to sparse_init_nid()
>  * we check range by check_pfn_span() before calling
>    sparse_add_section()
>
>Also, the counterpart of __populate_section_memmap(), we don't do such
>calculation and check since the range is checked by check_pfn_span() in
>__remove_pages().
>
>Clear the calculation and check to keep it simple and comply with its
>counterpart.
>
>Signed-off-by: Wei Yang <richard.weiyang@linux.alibaba.com>
>

Hi, Andrew,

Is this one picked up?

>---
>v2:
>  * add a warn on once for unaligned range, suggested by David
>---
> mm/sparse-vmemmap.c | 20 ++++++--------------
> 1 file changed, 6 insertions(+), 14 deletions(-)
>
>diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c
>index 0db7738d76e9..8d3a1b6287c5 100644
>--- a/mm/sparse-vmemmap.c
>+++ b/mm/sparse-vmemmap.c
>@@ -247,20 +247,12 @@ int __meminit vmemmap_populate_basepages(unsigned long start,
> struct page * __meminit __populate_section_memmap(unsigned long pfn,
> 		unsigned long nr_pages, int nid, struct vmem_altmap *altmap)
> {
>-	unsigned long start;
>-	unsigned long end;
>-
>-	/*
>-	 * The minimum granularity of memmap extensions is
>-	 * PAGES_PER_SUBSECTION as allocations are tracked in the
>-	 * 'subsection_map' bitmap of the section.
>-	 */
>-	end = ALIGN(pfn + nr_pages, PAGES_PER_SUBSECTION);
>-	pfn &= PAGE_SUBSECTION_MASK;
>-	nr_pages = end - pfn;
>-
>-	start = (unsigned long) pfn_to_page(pfn);
>-	end = start + nr_pages * sizeof(struct page);
>+	unsigned long start = (unsigned long) pfn_to_page(pfn);
>+	unsigned long end = start + nr_pages * sizeof(struct page);
>+
>+	if (WARN_ON_ONCE(!IS_ALIGNED(pfn, PAGES_PER_SUBSECTION) ||
>+		!IS_ALIGNED(nr_pages, PAGES_PER_SUBSECTION)))
>+		return NULL;
> 
> 	if (vmemmap_populate(start, end, nid, altmap))
> 		return NULL;
>-- 
>2.20.1 (Apple Git-117)

-- 
Wei Yang
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