linux-kernel - [PATCH 3.12 078/124] net: don't wait for order-3 page allocation

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Message-Id: <6088661c5342f33e3d667e866339b85ff985934b.1438076484.git.jslaby@suse.cz>
Date:	Tue, 28 Jul 2015 11:43:32 +0200
From:	Jiri Slaby <jslaby@...e.cz>
To:	stable@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, Shaohua Li <shli@...com>,
	Eric Dumazet <edumazet@...gle.com>, Chris Mason <clm@...com>,
	Debabrata Banerjee <dbavatar@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 3.12 078/124] net: don't wait for order-3 page allocation

From: Shaohua Li <shli@...com>

3.12-stable review patch.  If anyone has any objections, please let me know.

===============

[ Upstream commit fb05e7a89f500cfc06ae277bdc911b281928995d ]

We saw excessive direct memory compaction triggered by skb_page_frag_refill.
This causes performance issues and add latency. Commit 5640f7685831e0
introduces the order-3 allocation. According to the changelog, the order-3
allocation isn't a must-have but to improve performance. But direct memory
compaction has high overhead. The benefit of order-3 allocation can't
compensate the overhead of direct memory compaction.

This patch makes the order-3 page allocation atomic. If there is no memory
pressure and memory isn't fragmented, the alloction will still success, so we
don't sacrifice the order-3 benefit here. If the atomic allocation fails,
direct memory compaction will not be triggered, skb_page_frag_refill will
fallback to order-0 immediately, hence the direct memory compaction overhead is
avoided. In the allocation failure case, kswapd is waken up and doing
compaction, so chances are allocation could success next time.

alloc_skb_with_frags is the same.

The mellanox driver does similar thing, if this is accepted, we must fix
the driver too.

V3: fix the same issue in alloc_skb_with_frags as pointed out by Eric
V2: make the changelog clearer

Cc: Eric Dumazet <edumazet@...gle.com>
Cc: Chris Mason <clm@...com>
Cc: Debabrata Banerjee <dbavatar@...il.com>
Signed-off-by: Shaohua Li <shli@...com>
Acked-by: Eric Dumazet <edumazet@...gle.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
 net/core/skbuff.c | 4 +++-
 net/core/sock.c   | 4 +++-
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index fa8448a730a9..b01dd5f421da 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -367,9 +367,11 @@ refill:
 		for (order = NETDEV_FRAG_PAGE_MAX_ORDER; ;) {
 			gfp_t gfp = gfp_mask;

-			if (order)
+			if (order) {
 				gfp |= __GFP_COMP | __GFP_NOWARN |
 				       __GFP_NOMEMALLOC;
+				gfp &= ~__GFP_WAIT;
+			}
 			nc->frag.page = alloc_pages(gfp, order);
 			if (likely(nc->frag.page))
 				break;
diff --git a/net/core/sock.c b/net/core/sock.c
index f9ec2f5be1c0..2335a7a130f2 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -1907,8 +1907,10 @@ bool sk_page_frag_refill(struct sock *sk, struct page_frag *pfrag)
 	do {
 		gfp_t gfp = sk->sk_allocation;

-		if (order)
+		if (order) {
 			gfp |= __GFP_COMP | __GFP_NOWARN | __GFP_NORETRY;
+			gfp &= ~__GFP_WAIT;
+		}
 		pfrag->page = alloc_pages(gfp, order);
 		if (likely(pfrag->page)) {
 			pfrag->offset = 0;
-- 
2.4.6

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