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tcp: reduce memory footprint when listing tcp hostcache

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In tcp_hostcache_list, the sbuf used would need a large (~2MB)
blocking allocation of memory (M_WAITOK), when listing a
full hostcache. This may stall the requestor for an indeterminate
time.

A further optimization is to return the expected userspace
buffersize right away, rather than preparing the output of
each current entry of the hostcase, provided by: @tuexen.

This makes use of the ready-made functions of sbuf to work
with sysctl, and repeatedly drain the much smaller buffer.

PR: 254333
MFC after: 2 weeks
Reviewed By: #transport, tuexen
Sponsored by: NetApp, Inc.
Differential Revision: https://reviews.freebsd.org/D29471
This commit is contained in:
Richard Scheffenegger 2021-03-28 23:12:03 +02:00
parent 98727c6cd1
commit cb0dd7e122
1 changed files with 15 additions and 6 deletions
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21
sys/netinet/tcp_hostcache.c
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@ -628,7 +628,7 @@ sysctl_tcp_hc_list(SYSCTL_HANDLER_ARGS)
{
const int linesize = 128;
struct sbuf sb;
int i, error;
int i, error, len;
struct hc_metrics *hc_entry;
char ip4buf[INET_ADDRSTRLEN];
#ifdef INET6
@ -638,11 +638,22 @@ sysctl_tcp_hc_list(SYSCTL_HANDLER_ARGS)
if (jailed_without_vnet(curthread->td_ucred) != 0)
return (EPERM);
sbuf_new(&sb, NULL, linesize * (V_tcp_hostcache.cache_count + 1),
SBUF_INCLUDENUL);
/* Optimize Buffer length query by sbin/sysctl */
if (req->oldptr == NULL) {
len = (V_tcp_hostcache.cache_count + 1) * linesize;
return (SYSCTL_OUT(req, NULL, len));
}
error = sysctl_wire_old_buffer(req, 0);
if (error != 0) {
return(error);
}
/* Use a buffer for 16 lines */
sbuf_new_for_sysctl(&sb, NULL, 16 * linesize, req);
sbuf_printf(&sb,
"\nIP address MTU SSTRESH RTT RTTVAR "
"\nIP address MTU SSTRESH RTT RTTVAR "
" CWND SENDPIPE RECVPIPE HITS UPD EXP\n");
#define msec(u) (((u) + 500) / 1000)
@ -677,8 +688,6 @@ sysctl_tcp_hc_list(SYSCTL_HANDLER_ARGS)
}
#undef msec
error = sbuf_finish(&sb);
if (error == 0)
error = SYSCTL_OUT(req, sbuf_data(&sb), sbuf_len(&sb));
sbuf_delete(&sb);
return(error);
}