Free a slot in the slot table.
Mark the slot as free in the bitmap-based allocation table
by clearing a bit corresponding to the slotid.
Update lowest_free_slotid if freed slotid is lower than that.
Update highest_used_slotid. In the case the freed slotid
equals the highest_used_slotid, scan downwards for the next
highest used slotid using the optimized fls* functions.
Finally, wake up thread waiting on slot_tbl_waitq for a free slot
to become available.
Signed-off-by: Benny Halevy <bhalevy@xxxxxxxxxxx>
---
fs/nfs/nfs4proc.c | 54 +++++++++++++++++++++++++++++++++++++++++++++++++++++
1 files changed, 54 insertions(+), 0 deletions(-)
diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c
index 4ded3a5..d26f61d 100644
--- a/fs/nfs/nfs4proc.c
+++ b/fs/nfs/nfs4proc.c
@@ -243,6 +243,60 @@ static inline int bmp2idx(unsigned long *base, unsigned long *bmp,
}
/*
+ * nfs4_find_slot - free a slot and efficiently update slot table.
+ *
+ * freeing a slot is trivially done by clearing its respective bit
+ * in the bitmap.
+ * The lowest_free_slotid is updated if the freed slotid is lower than that.
+ * If the freed slotid equals highest_used_slotid we want to update it
+ * so that the server would be able to size down the slot table if needed,
+ * otherwise we know that the highest_used_slotid is still in use.
+ * When updating highest_used_slotid there may be "holes" in the bitmap
+ * so we need to scan down from highest_used_slotid to 0 looking for the now
+ * highest slotid in use.
+ * We use the fls cpu-optimized function to look for the last set bit in each
+ * word in the bitmap.
+ * If none found, highest_used_slotid is set to -1.
+ */
+static void
+nfs41_free_slot(struct nfs4_slot_table *tbl, struct nfs4_slot *slot)
+{
+ int slotid = slot_idx(tbl, slot);
+ unsigned long *used, u;
+ int bit;
+
+ spin_lock(&tbl->slot_tbl_lock);
+ /* clear used bit in bitmap */
+ used = idx2bmp(tbl->used_slots, slotid, &bit);
+ *used &= ~(1 << bit);
+
+ if (slotid < tbl->lowest_free_slotid)
+ tbl->lowest_free_slotid = slotid;
+
+ /* update highest_used_slotid when it is freed */
+ if (slotid == tbl->highest_used_slotid) {
+ tbl->highest_used_slotid = -1;
+ slotid--;
+ /* scan down for the highest used slotid */
+ while (slotid >= 0) {
+ used = idx2bmp(tbl->used_slots, slotid, NULL);
+ u = *used;
+ if (!u) {
+ /* all slots marked free in this word */
+ slotid -= BITS_PER_LONG;
+ continue;
+ }
+ bit = __fls(u);
+ tbl->highest_used_slotid = bmp2idx(tbl->used_slots,
+ used, bit);
+ break;
+ }
+ }
+ spin_unlock(&tbl->slot_tbl_lock);
+ rpc_wake_up_next(&tbl->slot_tbl_waitq);
+}
+
+/*
* nfs4_find_slot - efficiently look for a free slot
*
* nfs4_find_slot uses the ffz cpu-optimized function to look for an unset
--
1.6.0.2
--
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