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Optimise readng large number --server options at start up.

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When re-reading upstream servers from /etc/resolv.conf or other
sources that can change dnsmasq tries to avoid memory fragmentation by
re-using existing records that are being re-read unchanged. This
involves seaching all the server records for each new one installed.
During startup this search is pointless, and can cause long start
times with thousands of --server options because the work needed is
O(n^2). Handle this case more intelligently.  Thanks to Ye Zhou for
spotting the problem and an initial patch.
This commit is contained in:
Simon Kelley
2022-11-21 16:40:53 +00:00
parent d6d7527c95
commit 881eaa4dbc
3 changed files with 49 additions and 21 deletions
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55
src/domain-match.c
View File

@@ -546,11 +546,23 @@ static int order_qsort(const void *a, const void *b)
return rc;
}
/* When loading large numbers of server=.... lines during startup,
there's no possibility that there will be server records that can be reused, but
searching a long list for each server added grows as O(n^2) and slows things down.
This flag is set only if is known there may be free server records that can be reused.
There's a call to mark_servers(0) in read_opts() to reset the flag before
main config read. */
static int maybe_free_servers = 0;
/* Must be called before add_update_server() to set daemon->servers_tail */
void mark_servers(int flag)
{
struct server *serv, **up;
maybe_free_servers = !!flag;
daemon->servers_tail = NULL;
/* mark everything with argument flag */
@@ -667,27 +679,30 @@ int add_update_server(int flags,
and move to the end of the list, for order. The entry found may already
be at the end. */
struct server **up, *tmp;
for (serv = daemon->servers, up = &daemon->servers; serv; serv = tmp)
{
tmp = serv->next;
if ((serv->flags & SERV_MARK) &&
hostname_isequal(alloc_domain, serv->domain))
{
/* Need to move down? */
if (serv->next)
{
*up = serv->next;
daemon->servers_tail->next = serv;
daemon->servers_tail = serv;
serv->next = NULL;
}
break;
}
else
up = &serv->next;
}
serv = NULL;
if (maybe_free_servers)
for (serv = daemon->servers, up = &daemon->servers; serv; serv = tmp)
{
tmp = serv->next;
if ((serv->flags & SERV_MARK) &&
hostname_isequal(alloc_domain, serv->domain))
{
/* Need to move down? */
if (serv->next)
{
*up = serv->next;
daemon->servers_tail->next = serv;
daemon->servers_tail = serv;
serv->next = NULL;
}
break;
}
else
up = &serv->next;
}
if (serv)
{
free(alloc_domain);

5
src/option.c
View File

@@ -5753,7 +5753,10 @@ void read_opts(int argc, char **argv, char *compile_opts)
#endif
add_txt("servers.bind", NULL, TXT_STAT_SERVERS);
#endif
/* See comment above make_servers(). Optimises server-read code. */
mark_servers(0);
while (1)
{
#ifdef HAVE_GETOPT_LONG