CODEWITHSUNDEEP
linuxsocketsbuffer
user3097669
user3097669

Reputation: 33

Setting Socket Receive Buffer Size, gets truncated to 244KB

I'm trying to increase the size of my socket receive buffer size using setsockopt() on linux. I can set it successfully to any value below 244KB. Any value above 244KB gets truncated to 244KB.

There appears to be some sort of system limit in place, but I can't figure where it is coming from, as it doesn't correspond with values below:

$ cat /proc/sys/net/ipv4/tcp_rmem 
4096    87380   4194304
$ cat /proc/sys/net/ipv4/tcp_wmem 
4096    16384   4194304
$ cat /proc/sys/net/core/rmem_default 
124928
$ cat /proc/sys/net/core/wmem_default 
124928

The default value is 87380 as expected, but I can't increase it to 4194304. It gets limited to 244KB. Interestingly that value is 2X rmem_default, do I need to change that?

Thanks

Upvotes: 1

Views: 1431

Answers (1)

Prabhu
Prabhu

Reputation: 3541

From man page for TCP:

   The maximum sizes for socket buffers declared  via  the    SO_SNDBUF  and
   SO_RCVBUF  mechanisms  are  limited by the global net.core.rmem_max and
   net.core.wmem_max sysctls.  Note that TCP actually allocates twice  the
   size  of  the buffer requested in the setsockopt(2) call, and so a suc-
   ceeding getsockopt(2) call will not return the same size of  buffer  as
   requested  in  the  setsockopt(2)  call

So what you pass for SO_SNDBUF/SO_RCVBUF gets doubled while allocation. And as such you cannot pass the max value (4194304) in setsockopt

Upvotes: 3

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