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

Abhijeet Rastogi
2023-05-17T03:09:07Z

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@redhat.com/T/#u

Signed-off-by: Abhijeet Rastogi <abhijeet.1989@gmail.com>
---
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@gmail.com

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@gmail.com
---
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@gmail.com>