netdev - RFC limit sk_mem

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Message-ID: <20130522004541.GA17240@obelix.rh>
Date:	Tue, 21 May 2013 21:45:41 -0300
From:	Flavio Leitner <fbl@...hat.com>
To:	netdev@...r.kernel.org
Cc:	David Miller <davem@...emloft.net>,
	Eric Dumazet <eric.dumazet@...il.com>
Subject: RFC limit sk_mem_quantum to 8192


Hi,

The page size can be 64k on ppc64, so SK_MEM_QUANTUM increases to
that value as well.

net/ipv4/tcp.c:
...
        sysctl_tcp_wmem[0] = SK_MEM_QUANTUM;
        sysctl_tcp_wmem[1] = 16*1024;
        sysctl_tcp_wmem[2] = max(64*1024, max_share);

        sysctl_tcp_rmem[0] = SK_MEM_QUANTUM;
        sysctl_tcp_rmem[1] = 87380;
        sysctl_tcp_rmem[2] = max(87380, max_share);

and:
include/net/sock.h:
#define SK_MEM_QUANTUM ((int)PAGE_SIZE)

ppc64 config:
# CONFIG_PPC_4K_PAGES is not set
# CONFIG_PPC_16K_PAGES is not set
CONFIG_PPC_64K_PAGES=y
# CONFIG_PPC_256K_PAGES is not set

It seems too much for a minimum reserved memory. Also, the
other values are meaningless in this case because default
is only 16k and the maximum is limited to 64k.

This will require a modification in the
Documentation/networking/ip-sysctl.txt as well which states
that default minimum is 1 page.

Also, sk_mem_schedule() and friends will have to consider
that SK_MEM_QUANTUM might not be PAGE_SIZE anymore.

Well, the patch below illustrates what I am talking.
thanks,
fbl

diff --git a/include/net/sock.h b/include/net/sock.h
index 5d84de4..d52fa2d 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -954,7 +954,12 @@ static inline struct inode *SOCK_INODE(struct socket *socket)
 extern int __sk_mem_schedule(struct sock *sk, int size, int kind);
 extern void __sk_mem_reclaim(struct sock *sk);
 
+#if PAGE_SIZE < 8192
 #define SK_MEM_QUANTUM ((int)PAGE_SIZE)
+#else
+#define SK_MEM_QUANTUM ((int)8192)
+#endif
+
 #define SK_MEM_QUANTUM_SHIFT ilog2(SK_MEM_QUANTUM)
 #define SK_MEM_SEND	0
 #define SK_MEM_RECV	1

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