Find a free slot using bitmap-based allocation.
Use the optimized ffz function to find a zero bit
in the bitmap that indicates a free slot, starting
the search from the 'lowest_free_slotid' position.
If found, mark the slot as used in the bitmap, get
the slot's slotid and seqid, and update max_slotid
to be used by the SEQUENCE operation.
Also, update lowest_free_slotid for next search.
If no free slot was found the caller has to wait
for a free slot (outside the scope of this function)
Signed-off-by: Benny Halevy <bhalevy@xxxxxxxxxxx>
---
fs/nfs/nfs4proc.c | 88 ++++++++++++++++++++++++++++++++++++++++++
include/linux/nfs4_session.h | 5 ++
2 files changed, 93 insertions(+), 0 deletions(-)
diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c
index 08e7129..4ded3a5 100644
--- a/fs/nfs/nfs4proc.c
+++ b/fs/nfs/nfs4proc.c
@@ -207,6 +207,94 @@ static void renew_lease(const struct nfs_server *server, unsigned long timestamp
spin_unlock(&clp->cl_lock);
}
+#if defined(CONFIG_NFS_V4_1)
+
+/*
+ * idx2bmp - return pointer to bitmap word holding index "idx".
+ *
+ * inputs:
+ * @base points to bitmap.
+ * @idx slot index.
+ *
+ * output:
+ * @bit optional, *bit set to bit index of "idx" in the returned
+ * bitmap word.
+ */
+static inline unsigned long *idx2bmp(unsigned long *base, int idx, int *bit)
+{
+ base += idx / BITS_PER_LONG;
+ if (bit)
+ *bit = idx & (BITS_PER_LONG - 1);
+ return base;
+}
+
+/*
+ * bmp2idx - return absolute index of bmp:bit in bitmap.
+ *
+ * inputs:
+ * @base points to bitmap.
+ * @bmp points to bitmap word.
+ * @bit bit index in bitmap word.
+ */
+static inline int bmp2idx(unsigned long *base, unsigned long *bmp,
+ int bit)
+{
+ return ((bmp - base) * BITS_PER_LONG) + bit;
+}
+
+/*
+ * nfs4_find_slot - efficiently look for a free slot
+ *
+ * nfs4_find_slot uses the ffz cpu-optimized function to look for an unset
+ * bit in each word in the bitmap.
+ * Scan starts at lowest_free_slotid, which is a hint for the free slot,
+ * as all lower-numbered slots are known to be used.
+ * If found, we mark the slot as used, update the highest_used_slotid,
+ * and respectively set up the sequence operation args.
+ * The lowest_free_slotid is always set to the successive slotid.
+ * A pointer to the slot's seqid is returned if found, or NULL otherwise.
+ */
+static struct nfs4_slot *
+nfs4_find_slot(struct nfs4_slot_table *tbl, struct rpc_task *task)
+{
+ int bit, slotid;
+ struct nfs4_slot *slot = NULL;
+ unsigned long *used, u;
+
+ spin_lock(&tbl->slot_tbl_lock);
+ slotid = tbl->lowest_free_slotid;
+ while (slotid < tbl->max_slots) {
+ used = idx2bmp(tbl->used_slots, slotid, NULL);
+ u = *used;
+ if (u == ~0UL) {
+ /* all slots marked used in this word */
+ slotid += BITS_PER_LONG;
+ continue;
+ }
+ /* find first slot marked free in word */
+ bit = ffz(u);
+ slotid = bmp2idx(tbl->used_slots, used, bit);
+ /* mark slot used. note that we don't do that if
+ * slotid >= tbl->max_slots so not to confuse
+ * highest_used_slotid algorithm */
+ if (slotid < tbl->max_slots) {
+ *used |= (1 << bit);
+ if (slotid > tbl->highest_used_slotid)
+ tbl->highest_used_slotid = slotid;
+ slot = tbl->slots + slotid;
+ slotid++; /* for updating lowest_free_slot */
+ }
+ break;
+ }
+ tbl->lowest_free_slotid = slotid;
+ spin_unlock(&tbl->slot_tbl_lock);
+ dprintk("<-- %s slot %p slotid %d\n", __func__,
+ slot, slot ? slot_idx(tbl, slot) : -1);
+ return slot;
+}
+
+#endif /* CONFIG_NFS_V4_1 */
+
static void update_changeattr(struct inode *dir, struct nfs4_change_info *cinfo)
{
struct nfs_inode *nfsi = NFS_I(dir);
diff --git a/include/linux/nfs4_session.h b/include/linux/nfs4_session.h
index d534269..2960ba9 100644
--- a/include/linux/nfs4_session.h
+++ b/include/linux/nfs4_session.h
@@ -33,6 +33,11 @@ struct nfs4_slot_table {
* op for dynamic resizing */
};
+static inline int slot_idx(struct nfs4_slot_table *tbl, struct nfs4_slot *sp)
+{
+ return sp - tbl->slots;
+}
+
struct nfs4_channel {
struct nfs4_channel_attrs chan_attrs;
struct rpc_clnt *rpc_client;
--
1.6.0.2
--
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