[Devel] [PATCH RHEL7 COMMIT] ms/net: don't wait for order-3 page allocation

[Konstantin Khorenko]

The commit is pushed to "branch-rh7-3.10.0-693.17.1.vz7.43.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-693.17.1.vz7.43.4
------>
commit 497a0449ec62f49bc2f29f2e1a90154c6b536fa3
Author: Shaohua Li <shli at fb.com>
Date:   Wed Feb 14 13:17:33 2018 +0300

    ms/net: don't wait for order-3 page allocation
    
    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 at google.com>
    Cc: Chris Mason <clm at fb.com>
    Cc: Debabrata Banerjee <dbavatar at gmail.com>
    Signed-off-by: Shaohua Li <shli at fb.com>
    Acked-by: Eric Dumazet <edumazet at google.com>
    Signed-off-by: David S. Miller <davem at davemloft.net>
    
    https://jira.sw.ru/browse/PSBM-81488
    (cherry picked from commit fb05e7a89f500cfc06ae277bdc911b281928995d)
    Signed-off-by: Andrey Ryabinin <aryabinin at virtuozzo.com>
---
 net/core/skbuff.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 4147d7219589..dca9d1d9676b 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -4360,7 +4360,7 @@ struct sk_buff *alloc_skb_with_frags(unsigned long header_len,
 
 		while (order) {
 			if (npages >= 1 << order) {
-				page = alloc_pages(gfp_mask |
+				page = alloc_pages((gfp_mask & ~__GFP_WAIT) |
 						   __GFP_COMP |
 						   __GFP_NOWARN |
 						   __GFP_NORETRY,