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From:   "NeilBrown" <neilb@suse.de>
To:     Chuck Lever <chuck.lever@oracle.com>,
        "J. Bruce Fields" <bfields@fieldses.org>
Cc:     linux-nfs@vger.kernel.org
Subject: [PATCH] SUNRPC: use congestion_wait() in svc_alloc_args()
Date:   Mon, 06 Sep 2021 14:44:08 +1000
Message-id: <163090344807.19339.10071205771966144716@noble.neil.brown.name>
Precedence: bulk


Many places that need to wait before retrying a memory allocation use
congestion_wait().  xfs_buf_alloc_pages() is a good example which
follows a similar pattern to that in svc_alloc_args().

It make sense to do the same thing in svc_alloc_args(); This will allow
the allocation to be retried sooner if some backing device becomes
non-congested before the timeout.

Every call to congestion_wait() in the entire kernel passes BLK_RW_ASYNC
as the first argument, so we should so.

The second argument - an upper limit for waiting - seem fairly
arbitrary.  Many places use "HZ/50" or "HZ/10".  As there is no obvious
choice, it seems reasonable to leave the maximum time unchanged.

If a service using svc_alloc_args() is terminated, it may now have to
wait up to the full 500ms before termination completes as
congestion_wait() cannot be interrupted.  I don't believe this will be a
problem in practice, though it might be justification for using a
smaller timeout.

Signed-off-by: NeilBrown <neilb@suse.de>
---

I happened to notice this inconsistency between svc_alloc_args() and
xfs_buf_alloc_pages() despite them doing very similar things, so thought
I'd send a patch.

NeilBrown


 net/sunrpc/svc_xprt.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c
index 796eebf1787d..161433ae0fab 100644
--- a/net/sunrpc/svc_xprt.c
+++ b/net/sunrpc/svc_xprt.c
@@ -10,6 +10,7 @@
 #include <linux/freezer.h>
 #include <linux/kthread.h>
 #include <linux/slab.h>
+#include <linux/backing-dev.h>
 #include <net/sock.h>
 #include <linux/sunrpc/addr.h>
 #include <linux/sunrpc/stats.h>
@@ -682,12 +683,10 @@ static int svc_alloc_arg(struct svc_rqst *rqstp)
 			/* Made progress, don't sleep yet */
 			continue;
=20
-		set_current_state(TASK_INTERRUPTIBLE);
-		if (signalled() || kthread_should_stop()) {
-			set_current_state(TASK_RUNNING);
+		if (signalled() || kthread_should_stop())
 			return -EINTR;
-		}
-		schedule_timeout(msecs_to_jiffies(500));
+
+		congestion_wait(BLK_RW_ASYNC, msecs_to_jiffies(500));
 	}
 	rqstp->rq_page_end =3D &rqstp->rq_pages[pages];
 	rqstp->rq_pages[pages] =3D NULL; /* this might be seen in nfsd_splice_actor=
() */
--=20
2.33.0