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    SubjectRe: [v3.3-rc2+ PATCH] tcp: properly initialize tcp memory limits
    On 02/02/2012 02:07 PM, Jason Wang wrote:
    > 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@redhat.com>
    Acked-by: Glauber Costa <glommer@parallels.com>

    > ---
    > net/ipv4/sysctl_net_ipv4.c | 5 -----
    > net/ipv4/tcp.c | 4 ++--
    > 2 files changed, 2 insertions(+), 7 deletions(-)
    >
    > diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c
    > index 4cb9cd2..1eb8caa 100644
    > --- a/net/ipv4/sysctl_net_ipv4.c
    > +++ b/net/ipv4/sysctl_net_ipv4.c
    > @@ -815,11 +815,6 @@ 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);
    Ok, this is indeed a good change, since we avoid initializing it twice.

    > diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
    > index 06373b4..3a7514b 100644
    > --- a/net/ipv4/tcp.c
    > +++ b/net/ipv4/tcp.c
    > @@ -3218,7 +3218,6 @@ __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;
    > @@ -3287,7 +3286,8 @@ 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);

    Indeed, this ends up influencing the value of max_share used below to
    initialize the other fields.
    I like your change because now the limit variable is being set
    independently between the global (now per-cgroup) and the per-socket
    limits. (it previously was limit = sysctl_tcp_mem[1] << (PAGE_SHIFT-7))

    So in the end, I personally think this is even clearer than what we had
    before.

    Acked-by: Glauber Costa <glommer@parallels.com>


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