Date: Sun, 28 Mar 2021 21:53:08 GMT From: Richard Scheffenegger <rscheff@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-main@FreeBSD.org Subject: git: cb0dd7e122b8 - main - tcp: reduce memory footprint when listing tcp hostcache Message-ID: <202103282153.12SLr8St000589@gitrepo.freebsd.org>
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The branch main has been updated by rscheff: URL: https://cgit.FreeBSD.org/src/commit/?id=cb0dd7e122b8936ad61a141e65ef8ef874bfebe5 commit cb0dd7e122b8936ad61a141e65ef8ef874bfebe5 Author: Richard Scheffenegger <rscheff@FreeBSD.org> AuthorDate: 2021-03-28 21:12:03 +0000 Commit: Richard Scheffenegger <rscheff@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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