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.
Thanks!
Ezequiel.
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