pnfs: change layout state seqlock to a spinlock
This prepares for future changes, where the layout state needs
to change atomically with several other variables. In particular,
it will need to know if lo->segs is empty, as we test that instead
of manipulating the NFS_LAYOUT_STATEID_SET bit. Moreover, the
layoutstateid is not really a read-mostly structure, as it is
written almost as often as it is read.
The behavior of pnfs_get_layout_stateid is also slightly changed, so that
it no longer changes the stateid. Its name is changed to +pnfs_choose_layoutget_stateid.
Signed-off-by: Fred Isaman <iisaman@netapp.com>
Signed-off-by: Benny Halevy <bhalevy@panasas.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
diff --git a/fs/nfs/pnfs.c b/fs/nfs/pnfs.c
index 6736f9e..08313f53 100644
--- a/fs/nfs/pnfs.c
+++ b/fs/nfs/pnfs.c
@@ -258,9 +258,6 @@
/* List does not take a reference, so no need for put here */
list_del_init(&lo->plh_layouts);
spin_unlock(&clp->cl_lock);
- write_seqlock(&lo->plh_seqlock);
- clear_bit(NFS_LAYOUT_STATEID_SET, &lo->plh_flags);
- write_sequnlock(&lo->plh_seqlock);
dprintk("%s:Return\n", __func__);
}
@@ -319,69 +316,40 @@
}
}
-/* update lo->plh_stateid with new if is more recent
- *
- * lo->plh_stateid could be the open stateid, in which case we just use what given.
- */
+/* update lo->plh_stateid with new if is more recent */
static void
pnfs_set_layout_stateid(struct pnfs_layout_hdr *lo,
const nfs4_stateid *new)
{
- nfs4_stateid *old = &lo->plh_stateid;
- bool overwrite = false;
+ u32 oldseq, newseq;
- write_seqlock(&lo->plh_seqlock);
- if (!test_bit(NFS_LAYOUT_STATEID_SET, &lo->plh_flags) ||
- memcmp(old->stateid.other, new->stateid.other, sizeof(new->stateid.other)))
- overwrite = true;
- else {
- u32 oldseq, newseq;
-
- oldseq = be32_to_cpu(old->stateid.seqid);
- newseq = be32_to_cpu(new->stateid.seqid);
- if ((int)(newseq - oldseq) > 0)
- overwrite = true;
- }
- if (overwrite)
- memcpy(&old->stateid, &new->stateid, sizeof(new->stateid));
- write_sequnlock(&lo->plh_seqlock);
+ oldseq = be32_to_cpu(lo->plh_stateid.stateid.seqid);
+ newseq = be32_to_cpu(new->stateid.seqid);
+ if ((int)(newseq - oldseq) > 0)
+ memcpy(&lo->plh_stateid, &new->stateid, sizeof(new->stateid));
}
-static void
-pnfs_layout_from_open_stateid(struct pnfs_layout_hdr *lo,
- struct nfs4_state *state)
+int
+pnfs_choose_layoutget_stateid(nfs4_stateid *dst, struct pnfs_layout_hdr *lo,
+ struct nfs4_state *open_state)
{
- int seq;
+ int status = 0;
dprintk("--> %s\n", __func__);
- write_seqlock(&lo->plh_seqlock);
- do {
- seq = read_seqbegin(&state->seqlock);
- memcpy(lo->plh_stateid.data, state->stateid.data,
- sizeof(state->stateid.data));
- } while (read_seqretry(&state->seqlock, seq));
- set_bit(NFS_LAYOUT_STATEID_SET, &lo->plh_flags);
- write_sequnlock(&lo->plh_seqlock);
- dprintk("<-- %s\n", __func__);
-}
+ spin_lock(&lo->plh_inode->i_lock);
+ if (list_empty(&lo->plh_segs)) {
+ int seq;
-void
-pnfs_get_layout_stateid(nfs4_stateid *dst, struct pnfs_layout_hdr *lo,
- struct nfs4_state *open_state)
-{
- int seq;
-
- dprintk("--> %s\n", __func__);
- do {
- seq = read_seqbegin(&lo->plh_seqlock);
- if (!test_bit(NFS_LAYOUT_STATEID_SET, &lo->plh_flags)) {
- /* This will trigger retry of the read */
- pnfs_layout_from_open_stateid(lo, open_state);
- } else
- memcpy(dst->data, lo->plh_stateid.data,
- sizeof(lo->plh_stateid.data));
- } while (read_seqretry(&lo->plh_seqlock, seq));
+ do {
+ seq = read_seqbegin(&open_state->seqlock);
+ memcpy(dst->data, open_state->stateid.data,
+ sizeof(open_state->stateid.data));
+ } while (read_seqretry(&open_state->seqlock, seq));
+ } else
+ memcpy(dst->data, lo->plh_stateid.data, sizeof(lo->plh_stateid.data));
+ spin_unlock(&lo->plh_inode->i_lock);
dprintk("<-- %s\n", __func__);
+ return status;
}
/*
@@ -496,7 +464,6 @@
lo->plh_refcount = 1;
INIT_LIST_HEAD(&lo->plh_layouts);
INIT_LIST_HEAD(&lo->plh_segs);
- seqlock_init(&lo->plh_seqlock);
lo->plh_inode = ino;
return lo;
}