9:49 a.m.
Forwarding to devel(a)lists.nfs-ganesha.org so others can see also.
Frank
From: 方媛 [mailto:fang_yuan1004@163.com]
Sent: Friday, March 29, 2019 1:46 AM
To: malahal(a)us.ibm.com; ffilzlnx(a)mindspring.com
Cc: yanhuan(a)bwstor.com.cn
Subject: A question about ganesha drc can not be free
I have a question about ganasha drc ref count, can you help me. thank you.
I read the latest ganesha git codes, for the protocol V4.0 case, I find drc ref count will
not decrease to 0, so can not been inserted into the tcp_drc_recycle_q, I wonder how to
free expired drc?
1. At the begining of the request process, nfs_dupreq_start will call nfs_dupreq_get_drc,
either a new drc be allocated or an old drc be reused, the drc.ref is set to 0 at first
and then added to 1 as below
/* Avoid double reference of drc,
* setting xp_u2 under DRC_ST_LOCK */
req->rq_xprt->xp_u2 = (void *)drc;
(void)nfs_dupreq_ref_drc(drc); /* xprt ref */
DRC_ST_UNLOCK();
drc->d_u.tcp.recycle_time = 0;
then at the end of the nfs_dupreq_get_drc, drc.ref is added to 2 as below
/* call path ref */
(void)nfs_dupreq_ref_drc(drc);
PTHREAD_MUTEX_unlock(&drc->mtx);
if (drc_check_expired)
drc_free_expired();
2. After finish the request process, drc ref count will not decrease 1. Because I see
nfs_dupreq_finish will not decrease ref count every time, just when the drc->size >
drc->maxsize, will call nfs_dupreq_put_drc to decrease ref count.
/* conditionally retire entries */
dq_again:
if (drc_should_retire(drc)) { /* if drc->sixe < drc->maxsize, will not
call nfs_dupreq_put_drc to decrease the drc ref count */
......
TAILQ_REMOVE(&drc->dupreq_q, ov, fifo_q);
--(drc->size);
/* release dv's ref */
nfs_dupreq_put_drc(drc, DRC_FLAG_LOCKED);
/* drc->mtx gets unlocked in the above call! */
rbtree_x_cached_remove(&drc->xt, t, &ov->rbt_k, ov->hk);
}
so drc ref count will not decrease to 1 forever.
3. Then umount the connection, drc ref count will not decrease to 0,
static enum xprt_stat nfs_rpc_free_user_data(SVCXPRT *xprt)
{
if (xprt->xp_u2) {
nfs_dupreq_put_drc(xprt->xp_u2, DRC_FLAG_RELEASE); /* drc ref count is more then 1
*/
xprt->xp_u2 = NULL;
}
return XPRT_DESTROYED;
}
so drc can not insert to the tcp_drc_recycle_q, then how to free expired drc?
I will waiting for your reply, thanks very much.