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Commit 999d8795 authored by Ezequiel Garcia's avatar Ezequiel Garcia Committed by Pekka Enberg
Browse files

mm/slob: Drop usage of page->private for storing page-sized allocations 



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 Enberg <penberg@kernel.org>
Cc: Matt Mackall <mpm@selenic.com>
Acked-by: default avatarChristoph Lameter <cl@linux.com>
Signed-off-by: default avatarEzequiel Garcia <elezegarcia@gmail.com>
Signed-off-by: default avatarPekka Enberg <penberg@kernel.org>
parent 1b4f59e3

mm/slob.c

+10 −14
Original line number Diff line number Diff line
@@ -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);

	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;

	} else

		return sp->private;

}

EXPORT_SYMBOL(ksize);