[PATCH] tcp_mem initialization

[John Heffner <jheffner@psc.edu>]

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The current tcp_mem initialization gives values that are really too 
small for systems with ~256-768 MB of memory, and also for systems with 
larger page sizes (ia64).  This patch gives an alternate method of 
initialization that doesn't depend on the cache allocation functions, 
but I think should still provide a nice curve that gives a smaller 
fraction of total memory with small-memory systems, while maintaining 
the same upper bound (pressure at 1/2, max as 3/4) on larger memory systems.

   -John


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Change tcp_mem initialization function.  The fraction of total memory is now
a continuous function of memory size, and independent of page size.

Signed-off-by: John Heffner <jheffner@psc.edu>

---
commit a4461a36efb376bf01399cfd6f1ad15dc89a8794
tree 23b2fb9da52b45de8008fc7ea6bb8c10e3a3724b
parent 8b9909ded6922c33c221b105b26917780cfa497d
author John Heffner <jheffner@psc.edu> Wed, 14 Mar 2007 17:15:06 -0400
committer John Heffner <jheffner@psc.edu> Wed, 14 Mar 2007 17:15:06 -0400

 net/ipv4/tcp.c |   13 ++++++++++---
 1 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 74c4d10..3834b10 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -2458,11 +2458,18 @@ void __init tcp_init(void)
 		sysctl_max_syn_backlog = 128;
 	}
 
-	/* Allow no more than 3/4 kernel memory (usually less) allocated to TCP */
-	sysctl_tcp_mem[0] = (1536 / sizeof (struct inet_bind_hashbucket)) << order;
-	sysctl_tcp_mem[1] = sysctl_tcp_mem[0] * 4 / 3;
+	/* Set the pressure threshold to be a fraction of global memory that
+	 * is up to 1/2 at 256 MB, decreasing toward zero with the amount of
+	 * memory, with a floor of 128 pages.
+	 */
+	limit = min(nr_all_pages, 1UL<<(28-PAGE_SHIFT)) >> (20-PAGE_SHIFT);
+	limit = (limit * (nr_all_pages >> (20-PAGE_SHIFT))) >> (PAGE_SHIFT-11);
+	limit = max(limit, 128UL);
+	sysctl_tcp_mem[0] = limit / 4 * 3;
+	sysctl_tcp_mem[1] = limit;
 	sysctl_tcp_mem[2] = sysctl_tcp_mem[0] * 2;
 
+	/* Set per-socket limits to no more than 1/128 the pressure threshold */
 	limit = ((unsigned long)sysctl_tcp_mem[1]) << (PAGE_SHIFT - 7);
 	max_share = min(4UL*1024*1024, limit);