On 08/05/2016 05:24 AM, Andrew Morton wrote:
>>
>> it causes double align requirement for __get_vm_area_node() if parameter
>> size is power of 2 and VM_IOREMAP is set in parameter flags
>>
>> it is fixed by handling the specail case manually due to lack of
>> get_count_order() for long parameter
>>
>> ...
>>
>> --- a/mm/vmalloc.c
>> +++ b/mm/vmalloc.c
>> @@ -1357,11 +1357,16 @@ static struct vm_struct *__get_vm_area_node(unsigned long size,
>> {
>> struct vmap_area *va;
>> struct vm_struct *area;
>> + int ioremap_size_order;
>>
>> BUG_ON(in_interrupt());
>> - if (flags & VM_IOREMAP)
>> - align = 1ul << clamp_t(int, fls_long(size),
>> - PAGE_SHIFT, IOREMAP_MAX_ORDER);
>> + if (flags & VM_IOREMAP) {
>> + ioremap_size_order = fls_long(size);
>> + if (is_power_of_2(size) && size != 1)
>> + ioremap_size_order--;
>> + align = 1ul << clamp_t(int, ioremap_size_order, PAGE_SHIFT,
>> + IOREMAP_MAX_ORDER);
>> + }
>>
>> size = PAGE_ALIGN(size);
>> if (unlikely(!size))
>
> I'm having trouble with this, and a more complete description would
> have helped!
>
> As far as I can tell, the current code will decide the following:
>
> size=0x10000: alignment=0x10000
> size=0x0f000: alignment=0x8000
>
no, the current code doesn't achieve the above results as shown below
size=0x10000 -> fls_long(0x10000)=17 -> alignment=0x20000
size=0x0f000 -> fls_long(0x0f000)=16 -> alignment=0x10000
it is wrong for power of 2 value such as size=0x10000
> And your patch will change it so that
>
> size=0x10000: alignment=0x8000
> size=0x0f000: alignment=0x8000
>
> Correct?
>
no, my patch will results in the following calculations
size=0x10000: alignment=0x10000
size=0x0f000: alignment=0x10000
> If so, I'm struggling to see the sense in this. Shouldn't we be
> changing things so that
>
> size=0x10000: alignment=0x10000
> size=0x0f000: alignment=0x10000
>
> ?
okay, it is the aim of my patch as explained above
>
>
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