net: don't wait for order-3 page allocation

[ 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@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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 69ec61abfb37aee9ab8f6ba2f752189ccc7ff094..8207f8d7f665b14ff8c279c39dc948ef9c1060da 100644 (file)
--- 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 650dd58ebd050d795c158df00503f247925a2637..8ebfa52e5d70c8bdc808fef44e4df68f95342a7c 100644 (file)
--- 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;