On Fri, Oct 16, 2020 at 12:45:00PM +0200, mwilck@xxxxxxxx wrote:
> From: Martin Wilck <mwilck@xxxxxxxx>
>
> We were allocating 1025 poll fds, which is not optimal. Fix it, and make this
> more easily customizable in general. Use POLLFDS_BASE rather than the
> hard-coded "2" for the number of fds we poll besides client connections.
> Introduce a maximum number of clients that can connect. When this number is
> reached, we simply stop polling the accept socket, so that new connections
> aren't accepted any more. Don't attempt to realloc() the pollfd array if the
> number of clients decreases. It's unlikely to ever be more than one or two
> pages. Finally, there's no need to wake up every 5s. Our signal handling is
> robust. Just sleep forever in ppoll() if nothing happens.
>
> Signed-off-by: Martin Wilck <mwilck@xxxxxxxx>
> ---
> multipathd/uxlsnr.c | 70 ++++++++++++++++++++++++++++-----------------
> 1 file changed, 43 insertions(+), 27 deletions(-)
>
> diff --git a/multipathd/uxlsnr.c b/multipathd/uxlsnr.c
> index ce2b680..cd462b6 100644
> --- a/multipathd/uxlsnr.c
> +++ b/multipathd/uxlsnr.c
> @@ -41,14 +41,25 @@
> #include "cli.h"
> #include "uxlsnr.h"
>
> -static struct timespec sleep_time = {5, 0};
> -
> struct client {
> struct list_head node;
> int fd;
> };
>
> -#define MIN_POLLS 1023
> +/* The number of fds we poll on, other than individual client connections */
> +#define POLLFDS_BASE 2
> +#define POLLFD_CHUNK (4096 / sizeof(struct pollfd))
> +/* Minimum mumber of pollfds to reserve for clients */
> +#define MIN_POLLS (POLLFD_CHUNK - POLLFDS_BASE)
Reviewed-by: Benjamin Marzinski <bmarzins@xxxxxxxxxx>
I have one nitpick. This code looks like it's pretending to allocate
pages of memory, when it's not. Malloc's bookeeping space means that
this memory chunk will be larger than a page. Even if it was page sized,
unless userspace is specifically asking for page-aligned memory, it most
like won't get it. Since AFAIK there is no benefit to mallocing memory
in a specific size increment, it doesn't seem woirth adding any
complexity to make sure our mallocs do that.
-Ben
> +/*
> + * Max number of client connections allowed
> + * During coldplug, there may be a large number of "multipath -u"
> + * processes connecting.
> + */
> +#define MAX_CLIENTS (16384 - POLLFDS_BASE)
> +
> +/* Compile-time error if POLLFD_CHUNK is too small */
> +static __attribute__((unused)) char ___a[-(MIN_POLLS <= 0)];
>
> static LIST_HEAD(clients);
> static pthread_mutex_t client_lock = PTHREAD_MUTEX_INITIALIZER;
> @@ -282,13 +293,13 @@ void * uxsock_listen(uxsock_trigger_fn uxsock_trigger, long ux_sock,
> char *inbuf;
> char *reply;
> sigset_t mask;
> - int old_clients = MIN_POLLS;
> + int max_pfds = MIN_POLLS + POLLFDS_BASE;
> /* conf->sequence_nr will be 1 when uxsock_listen is first called */
> unsigned int sequence_nr = 0;
> struct watch_descriptors wds = { .conf_wd = -1, .dir_wd = -1 };
>
> condlog(3, "uxsock: startup listener");
> - polls = (struct pollfd *)MALLOC((MIN_POLLS + 2) * sizeof(struct pollfd));
> + polls = MALLOC(max_pfds * sizeof(*polls));
> if (!polls) {
> condlog(0, "uxsock: failed to allocate poll fds");
> exit_daemon();
> @@ -312,28 +323,33 @@ void * uxsock_listen(uxsock_trigger_fn uxsock_trigger, long ux_sock,
> list_for_each_entry(c, &clients, node) {
> num_clients++;
> }
> - if (num_clients != old_clients) {
> + if (num_clients + POLLFDS_BASE > max_pfds) {
> struct pollfd *new;
> - if (num_clients <= MIN_POLLS && old_clients > MIN_POLLS) {
> - new = REALLOC(polls, (2 + MIN_POLLS) *
> - sizeof(struct pollfd));
> - } else if (num_clients <= MIN_POLLS && old_clients <= MIN_POLLS) {
> - new = polls;
> - } else {
> - new = REALLOC(polls, (2 + num_clients) *
> - sizeof(struct pollfd));
> - }
> - if (!new) {
> - condlog(0, "%s: failed to realloc %d poll fds",
> - "uxsock", 2 + num_clients);
> - num_clients = old_clients;
> - } else {
> - old_clients = num_clients;
> + int n_new = max_pfds + POLLFD_CHUNK;
> +
> + new = REALLOC(polls, n_new * sizeof(*polls));
> + if (new) {
> + max_pfds = n_new;
> polls = new;
> + } else {
> + condlog(1, "%s: realloc failure, %d clients not served",
> + __func__,
> + num_clients + POLLFDS_BASE - max_pfds);
> + num_clients = max_pfds - POLLFDS_BASE;
> }
> }
> - polls[0].fd = ux_sock;
> - polls[0].events = POLLIN;
> + if (num_clients < MAX_CLIENTS) {
> + polls[0].fd = ux_sock;
> + polls[0].events = POLLIN;
> + } else {
> + /*
> + * New clients can't connect, num_clients won't grow
> + * to MAX_CLIENTS or higher
> + */
> + condlog(1, "%s: max client connections reached, pausing polling",
> + __func__);
> + polls[0].fd = -1;
> + }
>
> reset_watch(notify_fd, &wds, &sequence_nr);
> if (notify_fd == -1 || (wds.conf_wd == -1 && wds.dir_wd == -1))
> @@ -343,19 +359,19 @@ void * uxsock_listen(uxsock_trigger_fn uxsock_trigger, long ux_sock,
> polls[1].events = POLLIN;
>
> /* setup the clients */
> - i = 2;
> + i = POLLFDS_BASE;
> list_for_each_entry(c, &clients, node) {
> polls[i].fd = c->fd;
> polls[i].events = POLLIN;
> i++;
> - if (i >= 2 + num_clients)
> + if (i >= max_pfds)
> break;
> }
> n_pfds = i;
> pthread_cleanup_pop(1);
>
> /* most of our life is spent in this call */
> - poll_count = ppoll(polls, n_pfds, &sleep_time, &mask);
> + poll_count = ppoll(polls, n_pfds, NULL, &mask);
>
> handle_signals(false);
> if (poll_count == -1) {
> @@ -388,7 +404,7 @@ void * uxsock_listen(uxsock_trigger_fn uxsock_trigger, long ux_sock,
> }
>
> /* see if a client wants to speak to us */
> - for (i = 2; i < n_pfds; i++) {
> + for (i = POLLFDS_BASE; i < n_pfds; i++) {
> if (polls[i].revents & POLLIN) {
> struct timespec start_time;
>
> --
> 2.28.0
--
dm-devel mailing list
dm-devel@xxxxxxxxxx
https://www.redhat.com/mailman/listinfo/dm-devel
