[CC Mel]
On Fri 10-03-17 14:41:22, Andrew Morton wrote:
> From: Wei Yang <richard.weiyang@xxxxxxxxx>
> Subject: mm/sparse: refine usemap_size() a little
>
> Current implementation calculates usemap_size in two steps:
> * calculate number of bytes to cover these bits
> * calculate number of "unsigned long" to cover these bytes
>
> It would be more clear by:
> * calculate number of "unsigned long" to cover these bits
> * multiple it with sizeof(unsigned long)
>
> This patch refine usemap_size() a little to make it more easy to
> understand.
I haven't checked deeply yet but reading through 5c0e3066474b ("Fix
corruption of memmap on IA64 SPARSEMEM when mem_section is not a power
of 2") made me ask whether the case described in the commit message
still applies after this change or whether it has been considered at
all.
> Link: http://lkml.kernel.org/r/20170310043713.96871-1-richard.weiyang@xxxxxxxxx
> Signed-off-by: Wei Yang <richard.weiyang@xxxxxxxxx>
> Cc: Tejun Heo <tj@xxxxxxxxxx>
> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> ---
>
> mm/sparse.c | 5 +----
> 1 file changed, 1 insertion(+), 4 deletions(-)
>
> diff -puN mm/sparse.c~mm-sparse-refine-usemap_size-a-little mm/sparse.c
> --- a/mm/sparse.c~mm-sparse-refine-usemap_size-a-little
> +++ a/mm/sparse.c
> @@ -248,10 +248,7 @@ static int __meminit sparse_init_one_sec
>
> unsigned long usemap_size(void)
> {
> - unsigned long size_bytes;
> - size_bytes = roundup(SECTION_BLOCKFLAGS_BITS, 8) / 8;
> - size_bytes = roundup(size_bytes, sizeof(unsigned long));
> - return size_bytes;
> + return BITS_TO_LONGS(SECTION_BLOCKFLAGS_BITS) * sizeof(unsigned long);
> }
>
> #ifdef CONFIG_MEMORY_HOTPLUG
> _
>
> Patches currently in -mm which might be from richard.weiyang@xxxxxxxxx are
>
> mm-sparse-refine-usemap_size-a-little.patch
> mm-page_alloc-return-0-in-case-this-node-has-no-page-within-the-zone.patch
>
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--
Michal Hocko
SUSE Labs
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