On 09/04/2012 02:34 PM, Ezequiel Garcia wrote:
> Hi Glauber,
>
> On Tue, Sep 4, 2012 at 7:15 AM, Glauber Costa <glommer@xxxxxxxxxxxxx> wrote:
>> On 09/04/2012 02:13 PM, Ezequiel Garcia wrote:
>>> This field was being used to store size allocation so it could be
>>> retrieved by ksize(). However, it is a bad practice to not mark a page
>>> as a slab page and then use fields for special purposes.
>>> There is no need to store the allocated size and
>>> ksize() can simply return PAGE_SIZE << compound_order(page).
>>
>> What happens for allocations smaller than a page?
>> It seems you are breaking ksize for those.
>>
>
> Allocations smaller than a page save its own size on a header
> located at each returned pointer. This is documented at the beginning of slob:
>
> "Above this is an implementation of kmalloc/kfree. Blocks returned
> from kmalloc are prepended with a 4-byte header with the kmalloc size."
>
> For this objects (smaller than a page) ksize works fine:
>
> size_t ksize(const void *block) {
> [...]
> unsigned int *m = (unsigned int *)(block - align);
> return SLOB_UNITS(*m) * SLOB_UNIT;
>
> (see how ksize substract 'align' from block to find the header?)
>
> Of course, it's possible I've overlooked something, but I think this
> should work.
>
Ok. Slob also goes to the page allocator for higher order kmallocs,
so it should work.
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@xxxxxxxxx. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>