Hello!
On May 1, 2015, at 1:48 PM, Julia Lawall wrote:
>>> From: Julia Lawall <julia.law...@lip6.fr>
>>>
>>> Replace OBD_ALLOC, OBD_ALLOC_WAIT, OBD_ALLOC_PTR, and OBD_ALLOC_PTR_WAIT by
>>> kalloc/kcalloc, and OBD_FREE and OBD_FREE_PTR by kfree.
>>
>> Nak: James Simmons <jsimm...@infradead.org>
>>
>> A simple replace will not work. The OBD_ALLOC and OBD_FREE functions
>> allocate memory
>> anywhere from one page to 4MB in size. You can't use kmalloc for the 4MB
>> allocations.
>> Currently lustre uses a 4 page water mark to determine if we allocate using
>> vmalloc. Even
>> using kmalloc for 4 pages has shown high failure rates on some systems. It
>> gets even more
>> messy with 64K page systems like ppc64 boxes. Now I'm not suggesting to port
>> the larger
>> allocations to vmalloc either since issues have been founded with using
>> vmalloc. For example
>> when using large stripe count files the MDS rpc generated crosses the 4 page
>> line and vmalloc
>> is used. Using vmalloc caused a global spinlock to be taken which causes
>> meta data operations
>> to serialized on the MDS servers.
>
> It's not the LARGE functions that do the switching? For example OBD_ALLOC
> ends up at __OBD_MALLOC_VERBOSE, which as far as I can see calls kmalloc
> (with __GFP_ZERO, and hance the use of kzalloc).
This is true. We have OBD_ALLOC that is straight kmalloc and then we have
OBD_ALLOC_LARGE
that depends on allocation size whenever it's kmalloc or vmalloc.
Similarly we have OBD_FREE and OBD_FREE_LARGE (This one could be converted
straight into kvfree).
I think the patches look fine.
Bye,
Oleg--
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