Re: [patch][rfc] acpi: do not use kmem caches

Alexey Starikovskiy
2008-12-01T17:43:20Z

Nick Piggin wrote:
> On Mon, Dec 01, 2008 at 08:04:21PM +0300, Alexey Starikovskiy wrote:
>
>> Nick Piggin wrote:
>>
>>> Hmm.
>>> Acpi-Operand 2641 2773 64 59 1 : tunables 120 60 8
>>> : slabdata 47 47 0
>>> Acpi-ParseExt 0 0 64 59 1 : tunables 120 60 8
>>> : slabdata 0 0 0
>>> Acpi-Parse 0 0 40 92 1 : tunables 120 60 8
>>> : slabdata 0 0 0
>>> Acpi-State 0 0 80 48 1 : tunables 120 60 8
>>> : slabdata 0 0 0
>>> Acpi-Namespace 1711 1792 32 112 1 : tunables 120 60 8
>>> : slabdata 16 16 0
>>>
>>>
>>> Looks different for my thinkpad.
>>>
>>>
>> Probably this is SLUB vs. SLAB thing Pecca was talking about...
>>
>
> Sizes should not be bigger with SLUB. Although if you have SLUB debugging
> turned on then maybe the size gets padded with redzones, but in that
> configuration you don't expect memory saving anyway because padding bloats
> things up.
>
>
>
>> And, probably you run at 32-bit? This is part of my .config:
>>
>
> No, 64 bit.
>
>
>
>> --------------------------------------------
>> CONFIG_SLUB_DEBUG=y
>> # CONFIG_SLAB is not set
>> CONFIG_SLUB=y
>> # CONFIG_SLOB is not set
>> -------------------------------------------
>>
>> With your patch you would be able to save 64*(2773 - 2641) + 32 *
>> (1792-1711)= 8448 + 2592 = 11040 bytes of memory, less than 3 pages?
>>
>
> You don't account the cost of the kmem cache. Or fragmentation that
> can be caused with extra kmem caches. I guess neither is any problem
> with SLOB, which is used by tiny systems...
>
There is very small amount of fragmentation -- underfill, maybe 3 pages
out of 63, less than 5%.