On Mon, Dec 19, 2016 at 04:15:14PM +0100, Michal Hocko wrote:
>On Sun 18-12-16 14:47:49, Wei Yang wrote:
>> The base address is already guaranteed to be in the region by
>> memblock_search().
>
Hi, Michal
Nice to receive your comment.
>First of all the way how the check is removed is the worst possible...
>Apart from that it is really not clear to me why checking the base
>is not needed. You are mentioning memblock_search but what about other
>callers? adjust_range_page_size_mask e.g...
>
Hmm... the memblock_search() is called by memblock_is_region_memory(). Maybe I
paste the whole function here would clarify the change.
int __init_memblock memblock_is_region_memory(phys_addr_t base, phys_addr_t size)
{
int idx = memblock_search(&memblock.memory, base);
phys_addr_t end = base + memblock_cap_size(base, &size);
if (idx == -1)
return 0;
return memblock.memory.regions[idx].base <= base &&
(memblock.memory.regions[idx].base +
memblock.memory.regions[idx].size) >= end;
}
So memblock_search() will search "base" in memblock.memory. If "base" is not
in memblock.memory, idx would be -1. Then following code will not be executed.
And if the following code is executed, it means idx is not -1 and
memblock_search() has found the "base" in memblock.memory.regions[idx], which
is ture for statement (memblock.memory.regions[idx].base <= base).
>You also didn't mention what is the motivation of this change? What will
>work better or why it makes sense in general?
>
The purpose is to improve the code by reduce an extra check.
>Also this seems to be a general purpose function so it should better
>be robust.
>
I think it is as robust as it was.
>> This patch removes the check on base.
>>
>> Signed-off-by: Wei Yang <richard.weiyang@xxxxxxxxx>
>
>Without a proper justification and with the horrible way how it is done
>Nacked-by: Michal Hocko <mhocko@xxxxxxxx>
>
Not sure I make it clear or I may miss something?
>> ---
>> mm/memblock.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/mm/memblock.c b/mm/memblock.c
>> index 7608bc3..cd85303 100644
>> --- a/mm/memblock.c
>> +++ b/mm/memblock.c
>> @@ -1615,7 +1615,7 @@ int __init_memblock memblock_is_region_memory(phys_addr_t base, phys_addr_t size
>>
>> if (idx == -1)
>> return 0;
>> - return memblock.memory.regions[idx].base <= base &&
>> + return /* memblock.memory.regions[idx].base <= base && */
>> (memblock.memory.regions[idx].base +
>> memblock.memory.regions[idx].size) >= end;
>> }
>> --
>> 2.5.0
>>
>> --
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>
>--
>Michal Hocko
>SUSE Labs
--
Wei Yang
Help you, Help me
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