The branch main has been updated by rscheff:
URL:
https://cgit.FreeBSD.org/src/commit/?id=cb0dd7e122b8936ad61a141e65ef8ef874bfebe5
commit cb0dd7e122b8936ad61a141e65ef8ef874bfebe5
Author: Richard Scheffenegger <rsch...@freebsd.org>
AuthorDate: 2021-03-28 21:12:03 +0000
Commit: Richard Scheffenegger <rsch...@freebsd.org>
CommitDate: 2021-03-28 21:50:23 +0000
tcp: reduce memory footprint when listing tcp hostcache
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
---
sys/netinet/tcp_hostcache.c | 21 +++++++++++++++------
1 file changed, 15 insertions(+), 6 deletions(-)
diff --git a/sys/netinet/tcp_hostcache.c b/sys/netinet/tcp_hostcache.c
index de999bcfda22..5fe905d9abf5 100644
--- a/sys/netinet/tcp_hostcache.c
+++ b/sys/netinet/tcp_hostcache.c
@@ -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);
}
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