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Subject[PATCH v2 3/3] erofs: simplify try_to_claim_pcluster()
Date
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().

Signed-off-by: Gao Xiang <hsiangkao@redhat.com>
---
fs/erofs/zdata.c | 51 +++++++++++++++++++++++-------------------------
1 file changed, 24 insertions(+), 27 deletions(-)

diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c
index edd7325570e1..b1b6cd03046f 100644
--- a/fs/erofs/zdata.c
+++ b/fs/erofs/zdata.c
@@ -298,34 +298,33 @@ 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) {
- /*
- * type 2, link to the end of a existing open chain,
- * be careful that its submission itself is governed
- * by the original owned chain.
- */
- if (cmpxchg(&pcl->next, Z_EROFS_PCLUSTER_TAIL,
- *owned_head) != Z_EROFS_PCLUSTER_TAIL)
- goto retry;
+ /* so we can attach this pcluster to our submission chain. */
+ clt->mode = COLLECT_PRIMARY_FOLLOWED;
+ return;
+ }
+
+ /*
+ * 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) {
*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,
@@ -370,10 +369,8 @@ 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;
+
+ z_erofs_try_to_claim_pcluster(clt);
clt->cl = cl;
return 0;
}
--
2.18.4
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