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Commit 6fdf3375 authored by Gao Xiang's avatar Gao Xiang Committed by Gao Xiang
Browse files

erofs: simplify try_to_claim_pcluster() 

simplify try_to_claim_pcluster() by directly using cmpxchg() here
(the retry loop caused more overhead.) Also, move the chain loop
detection in and rename it to z_erofs_try_to_claim_pcluster().

Link: https://lore.kernel.org/r/20201208095834.3133565-3-hsiangkao@redhat.com


Reviewed-by: default avatarChao Yu <yuchao0@huawei.com>
Signed-off-by: default avatarGao Xiang <hsiangkao@redhat.com>
parent d25241a0

fs/erofs/zdata.c

+24 −27
Original line number Diff line number Diff line
@@ -305,34 +305,33 @@ static int z_erofs_attach_page(struct z_erofs_collector *clt, 
	return ret ? 0 : -EAGAIN;

}



static enum z_erofs_collectmode

try_to_claim_pcluster(struct z_erofs_pcluster *pcl,

		      z_erofs_next_pcluster_t *owned_head)

static void z_erofs_try_to_claim_pcluster(struct z_erofs_collector *clt)

{

	/* let's claim these following types of pclusters */

retry:

	if (pcl->next == Z_EROFS_PCLUSTER_NIL) {

		/* type 1, nil pcluster */

		if (cmpxchg(&pcl->next, Z_EROFS_PCLUSTER_NIL,

			    *owned_head) != Z_EROFS_PCLUSTER_NIL)

			goto retry;

	struct z_erofs_pcluster *pcl = clt->pcl;

	z_erofs_next_pcluster_t *owned_head = &clt->owned_head;



	/* type 1, nil pcluster (this pcluster doesn't belong to any chain.) */

	if (cmpxchg(&pcl->next, Z_EROFS_PCLUSTER_NIL,

		    *owned_head) == Z_EROFS_PCLUSTER_NIL) {

		*owned_head = &pcl->next;

		/* lucky, I am the followee :) */

		return COLLECT_PRIMARY_FOLLOWED;

	} else if (pcl->next == Z_EROFS_PCLUSTER_TAIL) {

		/* so we can attach this pcluster to our submission chain. */

		clt->mode = COLLECT_PRIMARY_FOLLOWED;

		return;

	}



	/*

		 * type 2, link to the end of a existing open chain,

		 * be careful that its submission itself is governed

		 * by the original owned chain.

	 * type 2, link to the end of an existing open chain, be careful

	 * that its submission is controlled by the original attached chain.

	 */

	if (cmpxchg(&pcl->next, Z_EROFS_PCLUSTER_TAIL,

			    *owned_head) != Z_EROFS_PCLUSTER_TAIL)

			goto retry;

		    *owned_head) == Z_EROFS_PCLUSTER_TAIL) {

		*owned_head = Z_EROFS_PCLUSTER_TAIL;

		return COLLECT_PRIMARY_HOOKED;

		clt->mode = COLLECT_PRIMARY_HOOKED;

		clt->tailpcl = NULL;

		return;

	}

	return COLLECT_PRIMARY;	/* :( better luck next time */

	/* type 3, it belongs to a chain, but it isn't the end of the chain */

	clt->mode = COLLECT_PRIMARY;

}



static int z_erofs_lookup_collection(struct z_erofs_collector *clt,
@@ -385,10 +384,8 @@ static int z_erofs_lookup_collection(struct z_erofs_collector *clt, 
	/* used to check tail merging loop due to corrupted images */

	if (clt->owned_head == Z_EROFS_PCLUSTER_TAIL)

		clt->tailpcl = pcl;

	clt->mode = try_to_claim_pcluster(pcl, &clt->owned_head);

	/* clean tailpcl if the current owned_head is Z_EROFS_PCLUSTER_TAIL */

	if (clt->owned_head == Z_EROFS_PCLUSTER_TAIL)

		clt->tailpcl = NULL;

	clt->pcl = pcl;

	z_erofs_try_to_claim_pcluster(clt);

	clt->pcl = pcl;

	clt->cl = cl;

	return 0;