Re: [PATCH] [9/20] Add blk_kmalloc/blk_alloc_pages

[Jens Axboe <jens.axboe@oracle.com>]

On Thu, Mar 13 2008, James Bottomley wrote:
> \On Fri, 2008-03-07 at 18:54 +0100, Andi Kleen wrote:
> > When a user is doing IO in the kernel and wants to avoid bouncing
> > it is best to just ask the block layer to allocate the memory for it.
> > This patch adds two simple wrappers: blk_kmalloc and blk_alloc_pages
> > and respective free functions to do this.
> > 
> > blk_alloc_pages is a little unusual in that it takes size
> > instead of order arguments -- i did this because I have later
> > patches to convert it over to a new allocator which does not 
> > require power of two for pages.
> 
> I really don't like this ... it's wedging something in the block layer
> that shouldn't be there just to avoid doing it properly in terms of
> allocations on the device dma_mask.
> 
> I also think the kfree takes a length part is asking for trouble because
> it's pretty fragile.
> 
> However, if Jens will ack it, I'll (reluctantly) add it.

I agree with you, I don't like it at all (for a variety of reasons).
Since callers need to remember size for free anyway (I've always hated
such interfaces), they may as well do their own allocations. I don't
think the block abstraction buys us anything.

If anything, add a generic allocator helper that you can pass a mask to
instead.

-- 
Jens Axboe