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Subject[PATCH 3.16.y-ckt 005/185] net: don't wait for order-3 page allocation
Date
3.16.7-ckt15 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Shaohua Li <shli@fb.com>

commit fb05e7a89f500cfc06ae277bdc911b281928995d upstream.

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@google.com>
Cc: Chris Mason <clm@fb.com>
Cc: Debabrata Banerjee <dbavatar@gmail.com>
Signed-off-by: Shaohua Li <shli@fb.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
[ luis: backported to 3.16: used davem's backport to 3.14 ]
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
---
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 dc27721ece4d..167a92c896b9 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -368,9 +368,11 @@ 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 a6ddd4ada315..9956e854d0e6 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -1914,8 +1914,10 @@ bool skb_page_frag_refill(unsigned int sz, struct page_frag *pfrag, gfp_t prio)
do {
gfp_t gfp = prio;

- 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;

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