[PATCH v3] ipvs: increase ip_vs_conn_tab_bits range for 64BIT

[Abhijeet Rastogi <abhijeet.1989@xxxxxxxxx>]

Current range [8, 20] is set purely due to historical reasons
because at the time, ~1M (2^20) was considered sufficient.
With this change, 27 is the upper limit for 64-bit, 20 otherwise.

Previous change regarding this limit is here.

Link: 
https://lore.kernel.org/all/86eabeb9dd62aebf1e2533926fdd13fed48bab1f.1631289960.git.aclaudi@xxxxxxxxxx/T/#u

Signed-off-by: Abhijeet Rastogi <abhijeet.1989@xxxxxxxxx>
---
The conversation for this started at: 

https://www.spinics.net/lists/netfilter/msg60995.html

The upper limit for algo is any bit size less than 32, so this
change will allow us to set bit size > 20. Today, it is common to have
RAM available to handle greater than 2^20 connections per-host.

Distros like RHEL already allow setting limits higher than 20.
---
Changes in v3:
- Fix text width in Kconfig, now text is 70 columns, excluding tab.
- Link to v2: 
https://lore.kernel.org/r/20230412-increase_ipvs_conn_tab_bits-v2-1-994c0df018e6@xxxxxxxxx

Changes in v2:
- Lower the ranges, 27 for 64bit, 20 otherwise
- Link to v1: 
https://lore.kernel.org/r/20230412-increase_ipvs_conn_tab_bits-v1-1-60a4f9f4c8f2@xxxxxxxxx
---
 net/netfilter/ipvs/Kconfig      | 27 ++++++++++++++-------------
 net/netfilter/ipvs/ip_vs_conn.c |  4 ++--
 2 files changed, 16 insertions(+), 15 deletions(-)

diff --git a/net/netfilter/ipvs/Kconfig b/net/netfilter/ipvs/Kconfig
index 271da8447b29..2a3017b9c001 100644
--- a/net/netfilter/ipvs/Kconfig
+++ b/net/netfilter/ipvs/Kconfig
@@ -44,7 +44,8 @@ config        IP_VS_DEBUG
 
 config IP_VS_TAB_BITS
        int "IPVS connection table size (the Nth power of 2)"
-       range 8 20
+       range 8 20 if !64BIT
+       range 8 27 if 64BIT
        default 12
        help
          The IPVS connection hash table uses the chaining scheme to handle
@@ -54,24 +55,24 @@ config      IP_VS_TAB_BITS
 
          Note the table size must be power of 2. The table size will be the
          value of 2 to the your input number power. The number to choose is
-         from 8 to 20, the default number is 12, which means the table size
-         is 4096. Don't input the number too small, otherwise you will lose
-         performance on it. You can adapt the table size yourself, according
-         to your virtual server application. It is good to set the table size
-         not far less than the number of connections per second multiplying
-         average lasting time of connection in the table.  For example, your
-         virtual server gets 200 connections per second, the connection lasts
-         for 200 seconds in average in the connection table, the table size
-         should be not far less than 200x200, it is good to set the table
-         size 32768 (2**15).
+         from 8 to 27 for 64BIT(20 otherwise), the default number is 12,
+         which means the table size is 4096. Don't input the number too
+         small, otherwise you will lose performance on it. You can adapt the
+         table size yourself, according to your virtual server application.
+         It is good to set the table size not far less than the number of
+         connections per second multiplying average lasting time of
+         connection in the table.  For example, your virtual server gets 200
+         connections per second, the connection lasts for 200 seconds in
+         average in the connection table, the table size should be not far
+         less than 200x200, it is good to set the table size 32768 (2**15).
 
          Another note that each connection occupies 128 bytes effectively and
          each hash entry uses 8 bytes, so you can estimate how much memory is
          needed for your box.
 
          You can overwrite this number setting conn_tab_bits module parameter
-         or by appending ip_vs.conn_tab_bits=? to the kernel command line
-         if IP VS was compiled built-in.
+         or by appending ip_vs.conn_tab_bits=? to the kernel command line if
+         IP VS was compiled built-in.
 
 comment "IPVS transport protocol load balancing support"
 
diff --git a/net/netfilter/ipvs/ip_vs_conn.c b/net/netfilter/ipvs/ip_vs_conn.c
index 13534e02346c..e1b9b52909a5 100644
--- a/net/netfilter/ipvs/ip_vs_conn.c
+++ b/net/netfilter/ipvs/ip_vs_conn.c
@@ -1484,8 +1484,8 @@ int __init ip_vs_conn_init(void)
        int idx;
 
        /* Compute size and mask */
-       if (ip_vs_conn_tab_bits < 8 || ip_vs_conn_tab_bits > 20) {
-               pr_info("conn_tab_bits not in [8, 20]. Using default value\n");
+       if (ip_vs_conn_tab_bits < 8 || ip_vs_conn_tab_bits > 27) {
+               pr_info("conn_tab_bits not in [8, 27]. Using default value\n");
                ip_vs_conn_tab_bits = CONFIG_IP_VS_TAB_BITS;
        }
        ip_vs_conn_tab_size = 1 << ip_vs_conn_tab_bits;

---
base-commit: 09a9639e56c01c7a00d6c0ca63f4c7c41abe075d
change-id: 20230412-increase_ipvs_conn_tab_bits-4322c90da216

Best regards,
-- 
Abhijeet Rastogi <abhijeet.1989@xxxxxxxxx>