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Commit 5e6d444e authored by Christoph Lameter's avatar Christoph Lameter Committed by Linus Torvalds
Browse files

SLUB: rework slab order determination 



In some cases SLUB is creating uselessly slabs that are larger than
slub_max_order. Also the layout of some of the slabs was not satisfactory.

Go to an iterarive approach.

Signed-off-by: default avatarChristoph Lameter <clameter@sgi.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 45edfa58

mm/slub.c

+52 −14
Original line number Diff line number Diff line
@@ -1577,35 +1577,73 @@ static int slub_nomerge; 
 * requested a higher mininum order then we start with that one instead of

 * the smallest order which will fit the object.

 */

static int calculate_order(int size)

static inline int slab_order(int size, int min_objects,

				int max_order, int fract_leftover)

{

	int order;

	int rem;



	for (order = max(slub_min_order, fls(size - 1) - PAGE_SHIFT);

			order < MAX_ORDER; order++) {

	for (order = max(slub_min_order,

				fls(min_objects * size - 1) - PAGE_SHIFT);

			order <= max_order; order++) {



		unsigned long slab_size = PAGE_SIZE << order;



		if (order < slub_max_order &&

				slab_size < slub_min_objects * size)

		if (slab_size < min_objects * size)

			continue;



		if (slab_size < size)

			continue;

		rem = slab_size % size;



		if (order >= slub_max_order)

		if (rem <= slab_size / fract_leftover)

			break;



		rem = slab_size % size;

	}



		if (rem <= slab_size / 8)

			break;

	return order;

}



static inline int calculate_order(int size)

{

	int order;

	int min_objects;

	int fraction;



	/*

	 * Attempt to find best configuration for a slab. This

	 * works by first attempting to generate a layout with

	 * the best configuration and backing off gradually.

	 *

	 * First we reduce the acceptable waste in a slab. Then

	 * we reduce the minimum objects required in a slab.

	 */

	min_objects = slub_min_objects;

	while (min_objects > 1) {

		fraction = 8;

		while (fraction >= 4) {

			order = slab_order(size, min_objects,

						slub_max_order, fraction);

			if (order <= slub_max_order)

				return order;

			fraction /= 2;

		}

		min_objects /= 2;

	}

	if (order >= MAX_ORDER)

		return -E2BIG;



	/*

	 * We were unable to place multiple objects in a slab. Now

	 * lets see if we can place a single object there.

	 */

	order = slab_order(size, 1, slub_max_order, 1);

	if (order <= slub_max_order)

		return order;



	/*

	 * Doh this slab cannot be placed using slub_max_order.

	 */

	order = slab_order(size, 1, MAX_ORDER, 1);

	if (order <= MAX_ORDER)

		return order;

	return -ENOSYS;

}



/*