Re: [PATCH net] netlink: do not enter direct reclaim from netlink_dump()

[David Miller <davem@davemloft.net>]

From: Eric Dumazet <eric.dumazet@gmail.com>
Date: Thu, 06 Oct 2016 04:13:18 +0900

> From: Eric Dumazet <edumazet@google.com>
> 
> Since linux-3.15, netlink_dump() can use up to 16384 bytes skb
> allocations.
> 
> Due to struct skb_shared_info ~320 bytes overhead, we end up using
> order-3 (on x86) page allocations, that might trigger direct reclaim and
> add stress.
> 
> The intent was really to attempt a large allocation but immediately
> fallback to a smaller one (order-1 on x86) in case of memory stress.
> 
> On recent kernels (linux-4.4), we can remove __GFP_DIRECT_RECLAIM to
> meet the goal. Old kernels would need to remove __GFP_WAIT
> 
> While we are at it, since we do an order-3 allocation, allow to use
> all the allocated bytes instead of 16384 to reduce syscalls during
> large dumps.
> 
> iproute2 already uses 32KB recvmsg() buffer sizes.
> 
> Alexei provided an initial patch downsizing to SKB_WITH_OVERHEAD(16384)
> 
> Fixes: 9063e21fb026 ("netlink: autosize skb lengthes")
> Signed-off-by: Eric Dumazet <edumazet@google.com>
> Reported-by: Alexei Starovoitov <ast@kernel.org>
> Cc: Greg Thelen <gthelen@google.com>
> ---
> Note: This will apply to net tree when it has synced with Linus tree.

Applied.