Re: [HPDD-discuss] [PATCH 2/11] Staging: lustre: fld: Use kzalloc and kfree
Hello!
On May 1, 2015, at 1:48 PM, Julia Lawall wrote:
>> From: Julia Lawall <Julia.Lawall(a)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 <jsimmons(a)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