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Commit 30d1cff8 authored by Alex Elder's avatar Alex Elder
Browse files

rbd: use binary search for snapshot lookup 



Use bsearch(3) to make snapshot lookup by id more efficient.  (There
could be thousands of snapshots, and conceivably many more.)

Signed-off-by: default avatarAlex Elder <elder@inktank.com>
Reviewed-by: default avatarJosh Durgin <josh.durgin@inktank.com>
parent 15228ede

drivers/block/rbd.c

+29 −5
Original line number Diff line number Diff line
@@ -33,6 +33,7 @@ 
#include <linux/ceph/mon_client.h>

#include <linux/ceph/decode.h>

#include <linux/parser.h>

#include <linux/bsearch.h>



#include <linux/kernel.h>

#include <linux/device.h>
@@ -819,16 +820,39 @@ static const char *_rbd_dev_v1_snap_name(struct rbd_device *rbd_dev, u32 which) 
	return kstrdup(snap_name, GFP_KERNEL);

}



/*

 * Snapshot id comparison function for use with qsort()/bsearch().

 * Note that result is for snapshots in *descending* order.

 */

static int snapid_compare_reverse(const void *s1, const void *s2)

{

	u64 snap_id1 = *(u64 *)s1;

	u64 snap_id2 = *(u64 *)s2;



	if (snap_id1 < snap_id2)

		return 1;

	return snap_id1 == snap_id2 ? 0 : -1;

}



/*

 * Search a snapshot context to see if the given snapshot id is

 * present.

 *

 * Returns the position of the snapshot id in the array if it's found,

 * or BAD_SNAP_INDEX otherwise.

 *

 * Note: The snapshot array is in kept sorted (by the osd) in

 * reverse order, highest snapshot id first.

 */

static u32 rbd_dev_snap_index(struct rbd_device *rbd_dev, u64 snap_id)

{

	struct ceph_snap_context *snapc = rbd_dev->header.snapc;

	u32 which;

	u64 *found;



	for (which = 0; which < snapc->num_snaps; which++)

		if (snapc->snaps[which] == snap_id)

			return which;

	found = bsearch(&snap_id, &snapc->snaps, snapc->num_snaps,

				sizeof (snap_id), snapid_compare_reverse);



	return BAD_SNAP_INDEX;

	return found ? (u32)(found - &snapc->snaps[0]) : BAD_SNAP_INDEX;

}



static const char *rbd_dev_v1_snap_name(struct rbd_device *rbd_dev,