On Thu, May 31, 2012 at 12:10 AM, Stefan Priebe - Profihost AG
<s.priebe@xxxxxxxxxxxx> wrote:
> Hi Marc, Hi Stefan,
>
> first thanks for all your help and time.
>
> I found the commit which results in this problem and it is TCP related
> but i'm still wondering if the expected behaviour of this commit is
> expected?
>
> The commit in question is:
> git show c43b874d5d714f271b80d4c3f49e05d0cbf51ed2
> commit c43b874d5d714f271b80d4c3f49e05d0cbf51ed2
> Author: Jason Wang <jasowang@xxxxxxxxxx>
> Date: Thu Feb 2 00:07:00 2012 +0000
>
> tcp: properly initialize tcp memory limits
>
> Commit 4acb4190 tries to fix the using uninitialized value
> introduced by commit 3dc43e3, but it would make the
> per-socket memory limits too small.
>
> This patch fixes this and also remove the redundant codes
> introduced in 4acb4190.
>
> Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
> Acked-by: Glauber Costa <glommer@xxxxxxxxxxxxx>
> Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
>
> diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c
> index 4cb9cd2..7a7724d 100644
> --- a/net/ipv4/sysctl_net_ipv4.c
> +++ b/net/ipv4/sysctl_net_ipv4.c
> @@ -778,7 +778,6 @@ EXPORT_SYMBOL_GPL(net_ipv4_ctl_path);
> static __net_init int ipv4_sysctl_init_net(struct net *net)
> {
> struct ctl_table *table;
> - unsigned long limit;
>
> table = ipv4_net_table;
> if (!net_eq(net, &init_net)) {
> @@ -815,11 +814,6 @@ static __net_init int ipv4_sysctl_init_net(struct
> net *net)
> net->ipv4.sysctl_rt_cache_rebuild_count = 4;
>
> tcp_init_mem(net);
> - limit = nr_free_buffer_pages() / 8;
> - limit = max(limit, 128UL);
> - net->ipv4.sysctl_tcp_mem[0] = limit / 4 * 3;
> - net->ipv4.sysctl_tcp_mem[1] = limit;
> - net->ipv4.sysctl_tcp_mem[2] = net->ipv4.sysctl_tcp_mem[0] * 2;
>
> net->ipv4.ipv4_hdr = register_net_sysctl_table(net,
> net_ipv4_ctl_path, table);
> diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
> index a34f5cf..37755cc 100644
> --- a/net/ipv4/tcp.c
> +++ b/net/ipv4/tcp.c
> @@ -3229,7 +3229,6 @@ __setup("thash_entries=", set_thash_entries);
>
> void tcp_init_mem(struct net *net)
> {
> - /* Set per-socket limits to no more than 1/128 the pressure
> threshold */
> unsigned long limit = nr_free_buffer_pages() / 8;
> limit = max(limit, 128UL);
> net->ipv4.sysctl_tcp_mem[0] = limit / 4 * 3;
> @@ -3298,7 +3297,8 @@ void __init tcp_init(void)
> sysctl_max_syn_backlog = max(128, cnt / 256);
>
> tcp_init_mem(&init_net);
> - limit = nr_free_buffer_pages() / 8;
> + /* Set per-socket limits to no more than 1/128 the pressure
> threshold */
> + limit = nr_free_buffer_pages() << (PAGE_SHIFT - 10);
> limit = max(limit, 128UL);
> max_share = min(4UL*1024*1024, limit);
>
Yeah, this might have affected the tcp performance. Looking at the
current linus tree this function looks more like it looked beforehand,
so it was probable reverted this way or another.
Yehuda
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