Re: [PATCH 02/22] Do not sanity check order in the fast path

Dave Hansen
2009-04-22T16:13:40Z

On Wed, 2009-04-22 at 14:53 +0100, Mel Gorman wrote:
> No user of the allocator API should be passing in an order >= MAX_ORDER
> but we check for it on each and every allocation. Delete this check and
> make it a VM_BUG_ON check further down the call path.

Should we get the check re-added to some of the upper-level functions,
then? Perhaps __get_free_pages() or things like alloc_pages_exact()?

I'm selfishly thinking of what I did in profile_init(). Can I slab
alloc it? Nope. Page allocator? Nope. Oh, well, try vmalloc():

prof_buffer = kzalloc(buffer_bytes, GFP_KERNEL);
if (prof_buffer)
return 0;

prof_buffer = alloc_pages_exact(buffer_bytes, GFP_KERNEL|__GFP_ZERO);
if (prof_buffer)
return 0;

prof_buffer = vmalloc(buffer_bytes);
if (prof_buffer)
return 0;

free_cpumask_var(prof_cpu_mask);
return -ENOMEM;

Same thing in __kmalloc_section_memmap():

page = alloc_pages(GFP_KERNEL|__GFP_NOWARN, get_order(memmap_size));
if (page)
goto got_map_page;

ret = vmalloc(memmap_size);
if (ret)
goto got_map_ptr;

I depend on the allocator to tell me when I've fed it too high of an
order. If we really need this, perhaps we should do an audit and then
add a WARN_ON() for a few releases to catch the stragglers.

-- Dave