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nfs41: free slot

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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@panasas.com>
[nfs41: free slot use slotid]
Signed-off-by: Andy Adamson <andros@netapp.com>
Signed-off-by: Benny Halevy <bhalevy@panasas.com>
[nfs41: use find_first_zero_bit for nfs4_find_slot]
    While at it, obliterate lowest_free_slotid and fix-up related comments.
    As per review comment 21/85.
Signed-off-by: Benny Halevy <bhalevy@panasas.com>
[nfs41: use __clear_bit for nfs4_free_slot]
    While at it, fix-up function comment.
    Part of review comment 22/85.
Signed-off-by: Benny Halevy <bhalevy@panasas.com>
[nfs41: use find_last_bit in nfs4_free_slot to determine highest used slot.]
Signed-off-by: Benny Halevy <bhalevy@panasas.com>
[nfs41: rpc_sleep_on slot_tbl_waitq must be called under slot_tbl_lock]
    Otherwise there's a race (we've hit) with nfs4_free_slot where
    nfs41_setup_sequence sees a full slot table, unlocks slot_tbl_lock,
    nfs4_free_slots happen concurrently and call rpc_wake_up_next
    where there's nobody to wake up yet, context goes back to
    nfs41_setup_sequence which goes to sleep when the slot table
    is actually empty now and there's no-one to wake it up anymore.
Signed-off-by: Benny Halevy <bhalevy@panasas.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
This commit is contained in:
Andy Adamson 2009-04-01 09:22:16 -04:00 committed by Benny Halevy
parent fbcd4abcb3
commit e2c4ab3ce2
1 changed files with 36 additions and 0 deletions
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36
fs/nfs/nfs4proc.c
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@ -273,6 +273,42 @@ static void renew_lease(const struct nfs_server *server, unsigned long timestamp
#if defined(CONFIG_NFS_V4_1)
/*
* nfs4_free_slot - free a slot and efficiently update slot table.
*
* freeing a slot is trivially done by clearing its respective bit
* in the bitmap.
* 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.
* If none found, highest_used_slotid is set to -1.
*/
static void
nfs4_free_slot(struct nfs4_slot_table *tbl, u8 free_slotid)
{
int slotid = free_slotid;
spin_lock(&tbl->slot_tbl_lock);
/* clear used bit in bitmap */
__clear_bit(slotid, tbl->used_slots);
/* update highest_used_slotid when it is freed */
if (slotid == tbl->highest_used_slotid) {
slotid = find_last_bit(tbl->used_slots, tbl->max_slots);
if (slotid >= 0 && slotid < tbl->max_slots)
tbl->highest_used_slotid = slotid;
else
tbl->highest_used_slotid = -1;
}
rpc_wake_up_next(&tbl->slot_tbl_waitq);
spin_unlock(&tbl->slot_tbl_lock);
dprintk("%s: free_slotid %u highest_used_slotid %d\n", __func__,
free_slotid, tbl->highest_used_slotid);
}
/*
* nfs4_find_slot - efficiently look for a free slot
*