On Thu, 18 Oct 2012, 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).
>
> Cc: Pekka Penberg <penberg@xxxxxxxxxx>
Is Pekka Penberg the long distant cousin of Pekka Enberg? :) You should
probably cc the author of slob, Matt Mackall <mpm@xxxxxxxxxxx>, on slob
patches.
> Acked-by: Christoph Lameter <cl@xxxxxxxxx>
> Signed-off-by: Ezequiel Garcia <elezegarcia@xxxxxxxxx>
> ---
> mm/slob.c | 24 ++++++++++--------------
> 1 files changed, 10 insertions(+), 14 deletions(-)
>
> diff --git a/mm/slob.c b/mm/slob.c
> index a08e468..06a5ec7 100644
> --- a/mm/slob.c
> +++ b/mm/slob.c
> @@ -28,9 +28,8 @@
> * from kmalloc are prepended with a 4-byte header with the kmalloc size.
> * If kmalloc is asked for objects of PAGE_SIZE or larger, it calls
> * alloc_pages() directly, allocating compound pages so the page order
> - * does not have to be separately tracked, and also stores the exact
> - * allocation size in page->private so that it can be used to accurately
> - * provide ksize(). These objects are detected in kfree() because slob_page()
> + * does not have to be separately tracked.
> + * These objects are detected in kfree() because PageSlab()
> * is false for them.
> *
> * SLAB is emulated on top of SLOB by simply calling constructors and
> @@ -455,11 +454,6 @@ __do_kmalloc_node(size_t size, gfp_t gfp, int node, unsigned long caller)
> if (likely(order))
> gfp |= __GFP_COMP;
> ret = slob_new_pages(gfp, order, node);
> - if (ret) {
> - struct page *page;
> - page = virt_to_page(ret);
> - page->private = size;
> - }
>
> trace_kmalloc_node(caller, ret,
> size, PAGE_SIZE << order, gfp, node);
> @@ -514,18 +508,20 @@ EXPORT_SYMBOL(kfree);
> size_t ksize(const void *block)
> {
> struct page *sp;
> + int align;
> + unsigned int *m;
>
> BUG_ON(!block);
> if (unlikely(block == ZERO_SIZE_PTR))
> return 0;
>
> sp = virt_to_page(block);
> - if (PageSlab(sp)) {
> - int align = max(ARCH_KMALLOC_MINALIGN, ARCH_SLAB_MINALIGN);
> - unsigned int *m = (unsigned int *)(block - align);
> - return SLOB_UNITS(*m) * SLOB_UNIT;
> - } else
> - return sp->private;
> + if (unlikely(!PageSlab(sp)))
> + return PAGE_SIZE << compound_order(sp);
> +
> + align = max(ARCH_KMALLOC_MINALIGN, ARCH_SLAB_MINALIGN);
> + m = (unsigned int *)(block - align);
> + return SLOB_UNITS(*m) * SLOB_UNIT;
> }
> EXPORT_SYMBOL(ksize);
>
--
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