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

Alexey Starikovskiy
2008-12-01T17:32:45Z

Christoph Hellwig wrote:
> On Mon, Dec 01, 2008 at 05:14:36PM +0300, Alexey Starikovskiy wrote:
>
>> Why then you try to delete ACPICA code, which might be just disabled by
>> undefining ACPI_USE_LOCAL_CACHE?
>> If you do want to go that path, you need to create patch against ACPICA, not
>> Linux code.
>>
>
> Sorry dude, but that's not how Linux development works. Please talk to
> some intel OTC folks to get an advice on how it does.
>
>
We are not speaking about Linux code here -- Nick changed ACPICA files.
And he already admits, that his patch is at least half-way wrong.
Sorry dude, ACPICA code is not Linux only, so one needs some care while
dropping some functionality from it.
>>> Ah OK I misread, that's the cache's freelist... ACPI shouldn't be poking
>>> this button inside the slab allocator anyway, honestly. What is it
>>> for?
>>>
>>>
>> And it is not actually used -- you cannot unload ACPI interpreter, and
>> this function is called only from there.
>>
>
> Care to remove all this dead code?
>
>
It is used at least in Windows userspace programs. So, removing these 4
lines only from Linux will
create another headache for Len during his merging of each new ACPICA
release into Linux.
>>> Is there a reasonable performance or memory win by using kmem cache? If
>>> not, then they should not be used
>>>
>> ACPI is still working in machines with several megabytes of RAM and
>> 100mhz Pentium processors. Do you say we should just not consider them
>> any longer?
>> If so, then just delete all ACPICA caches altogether.
>>
>
> As Nick is trying to explain you for a while it's not actually going
> to be a performance benefit for these, quite contrary because of how
> slab caches waste a lot of memory when only used very lightly or not
> at all.
>
>
If you care to do the math, and I helped you in another posting, he may
save about 11k in 32bit mode on thinkpad, and loose 70k in 64bit mode on
similar thinkpad.

Regards,
Alex.