netdev - [RFC] net: use atomic allocation for order-3 page allocation

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Date:	Thu, 11 Jun 2015 13:24:31 -0700
From:	Shaohua Li <shli@...com>
To:	<netdev@...r.kernel.org>
CC:	<davem@...emloft.net>, <Kernel-team@...com>,
	Eric Dumazet <edumazet@...gle.com>
Subject: [RFC] net: use atomic allocation for order-3 page allocation

We saw excessive memory compaction triggered by skb_page_frag_refill.
This causes performance issues. Commit 5640f7685831e0 introduces the
order-3 allocation to improve performance. But memory compaction has
high overhead. The benefit of order-3 allocation can't compensate the
overhead of 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, compaction will not be triggered and we will fallback
to order-0 immediately.

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

Cc: Eric Dumazet <edumazet@...gle.com>
Signed-off-by: Shaohua Li <shli@...com>
---
 net/core/sock.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/core/sock.c b/net/core/sock.c
index 292f422..e9855a4 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -1883,7 +1883,7 @@ bool skb_page_frag_refill(unsigned int sz, struct page_frag *pfrag, gfp_t gfp)

 	pfrag->offset = 0;
 	if (SKB_FRAG_PAGE_ORDER) {
-		pfrag->page = alloc_pages(gfp | __GFP_COMP |
+		pfrag->page = alloc_pages((gfp & ~__GFP_WAIT) | __GFP_COMP |
 					  __GFP_NOWARN | __GFP_NORETRY,
 					  SKB_FRAG_PAGE_ORDER);
 		if (likely(pfrag->page)) {
-- 
1.8.1

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