[PATCH net-next] netlink: do not enter direct reclaim from netlink_trim()

[PATCH net-next] netlink: do not enter direct reclaim from netlink_trim()

[Eric Dumazet]

From: Eric Dumazet <edumazet@google.com>

In commit d35c99ff77ecb ("netlink: do not enter direct reclaim from
netlink_dump()") we made sure to not trigger expensive memory reclaim.

Problem is that a bit later, netlink_trim() might be called and
trigger memory reclaim.

netlink_trim() should be best effort, and really as fast as possible.
Under memory pressure, it is fine to not trim this skb.

Signed-off-by: Eric Dumazet <edumazet@google.com>
---
 net/netlink/af_netlink.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index 161b628ab2b08bf4321dbe617022c4c50486534d..edcc1e19ad532641f51f6809b8c90d1e377081ff 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -1210,7 +1210,9 @@ static struct sk_buff *netlink_trim(struct sk_buff *skb, gfp_t allocation)
 		skb = nskb;
 	}
 
-	if (!pskb_expand_head(skb, 0, -delta, allocation))
+	if (!pskb_expand_head(skb, 0, -delta,
+			      (allocation & ~__GFP_DIRECT_RECLAIM) |
+			      __GFP_NOWARN | __GFP_NORETRY))
 		skb->truesize -= delta;
 
 	return skb;

Re: [PATCH net-next] netlink: do not enter direct reclaim from netlink_trim()

[Alexei Starovoitov]

On Fri, Jan 13, 2017 at 09:11:22AM -0800, Eric Dumazet wrote:
> From: Eric Dumazet <edumazet@google.com>
> 
> In commit d35c99ff77ecb ("netlink: do not enter direct reclaim from
> netlink_dump()") we made sure to not trigger expensive memory reclaim.
> 
> Problem is that a bit later, netlink_trim() might be called and
> trigger memory reclaim.
> 
> netlink_trim() should be best effort, and really as fast as possible.
> Under memory pressure, it is fine to not trim this skb.
> 
> Signed-off-by: Eric Dumazet <edumazet@google.com>

Thanks!
Acked-by: Alexei Starovoitov <ast@kernel.org>

Re: [PATCH net-next] netlink: do not enter direct reclaim from netlink_trim()

[David Miller]

From: Eric Dumazet <eric.dumazet@gmail.com>
Date: Fri, 13 Jan 2017 09:11:22 -0800

> From: Eric Dumazet <edumazet@google.com>
> 
> In commit d35c99ff77ecb ("netlink: do not enter direct reclaim from
> netlink_dump()") we made sure to not trigger expensive memory reclaim.
> 
> Problem is that a bit later, netlink_trim() might be called and
> trigger memory reclaim.
> 
> netlink_trim() should be best effort, and really as fast as possible.
> Under memory pressure, it is fine to not trim this skb.
> 
> Signed-off-by: Eric Dumazet <edumazet@google.com>

Applied, thanks Eric.