[CRIU] [PATCH v3 08/10] files: Make tasks set their own service_fd_base

[Andrei Vagin]

On Tue, Jan 09, 2018 at 02:43:22PM +0300, Kirill Tkhai wrote:
> On 31.12.2017 08:30, Andrei Vagin wrote:
> > On Fri, Dec 29, 2017 at 12:36:17PM +0300, Kirill Tkhai wrote:
> >> Currently, we set rlim(RLIMIT_NOFILE) unlimited
> >> and service_fd_rlim_cur to place service fds.
> >> This leads to a signify problem: every task uses
> >> the biggest possible files_struct in kernel, and
> >> it consumes excess memory after restore
> >> in comparation to dump. In some situations this
> >> may end in restore fail as there is no enough
> >> memory in memory cgroup of on node.
> >>
> >> The patch fixes the problem by introducing
> >> task-measured service_fd_base. It's calculated
> >> in dependence of max used file fd and is placed
> >> near the right border of kernel-allocated memory
> >> hunk for task's fds (see alloc_fdtable() for
> >> details). This reduces kernel-allocated files_struct
> >> to 512 fds for the most process in standard linux
> >> system (I've analysed the processes in my work system).
> >>
> >> Also, since the "standard processes" will have the same
> >> service_fd_base, clone_service_fd() won't have to
> >> actualy dup() their service fds for them like we
> >> have at the moment. This is the one of reasons why
> >> we still keep service fds as a range of fds,
> >> and do not try to use unused holes in task fds.
> >>
> >> Signed-off-by: Kirill Tkhai <ktkhai at virtuozzo.com>
> >>
> >> v2: Add a handle for very big fd numbers near service_fd_rlim_cur.
> >> v3: Fix excess accounting for nr equal to pow 2 minus 1.
> >> ---
> >>  criu/util.c |   57 +++++++++++++++++++++++++++++++++++++++++++++++++++++----
> >>  1 file changed, 53 insertions(+), 4 deletions(-)
> >>
> >> diff --git a/criu/util.c b/criu/util.c
> >> index d45bb7d61..1e78f74c5 100644
> >> --- a/criu/util.c
> >> +++ b/criu/util.c
> >> @@ -527,7 +527,7 @@ int close_service_fd(enum sfd_type type)
> >>  static void move_service_fd(struct pstree_item *me, int type, int new_id, int new_base)
> >>  {
> >>  	int old = get_service_fd(type);
> >> -	int new = __get_service_fd(type, new_id);
> >> +	int new = new_base - type - SERVICE_FD_MAX * new_id;
> >>  	int ret;
> >>  
> >>  	if (old < 0)
> >> @@ -540,24 +540,73 @@ static void move_service_fd(struct pstree_item *me, int type, int new_id, int ne
> >>  		close(old);
> >>  }
> >>  
> >> +static int choose_service_fd_base(struct pstree_item *me)
> >> +{
> >> +	int nr, real_nr, fdt_nr = 1, id = rsti(me)->service_fd_id;
> >> +
> >> +	if (rsti(me)->fdt) {
> >> +		/* The base is set by owner of fdt (id 0) */
> >> +		if (id != 0)
> >> +			return service_fd_base;
> >> +		fdt_nr = rsti(me)->fdt->nr;
> >> +	}
> >> +	/* Now find process's max used fd number */
> > 
> > Why don't we take into account file descriptors, which criu opens to
> > restore vma-s. They are closed in restore_mapping(). Can they intersect
> > with service fds? Is it a problem?
> 
> They may intersect, and their number is unlimited. But I based on the logic,
> that nobody closes a service fd in restore_mapping(). So nobody can occupy
> the closed number.

For example:

If two processes share fdtable-s, a process which doesn't restore
files, exits from prepare_fds() with closed CR_FD_PID_PROC.

prepare_fds()
	close_pid_proc()
open_vmas()
        if (vma->vm_open(pid, vma)) {

> 
> We may introduce sanity check in close_service_fd(). Something like
> a global variable, which indicates, that service fd close is prohibited.
> This variable will be set up since task in forked and till service fds are
> rebased. Not sure, we really need this.
>  
> >> +	if (!list_empty(&rsti(me)->fds))
> >> +		nr = list_entry(rsti(me)->fds.prev,
> >> +				struct fdinfo_list_entry, ps_list)->fe->fd;
> >> +	else
> >> +		nr = -1;
> >> +
> >> +	nr = max(nr, inh_fd_max);
> >> +	/*
> >> +	 * Service fds go after max fd near right border of alignment:
> >> +	 *
> >> +	 * ...|max_fd|max_fd+1|...|sfd first|...|sfd last (aligned)|
> >> +	 *
> >> +	 * So, they take maximum numbers of area allocated by kernel.
> >> +	 * See linux alloc_fdtable() for details.
> >> +	 */
> >> +	nr += (SERVICE_FD_MAX - SERVICE_FD_MIN) * fdt_nr;
> >> +	nr += 16; /* Safety pad */
> >> +	real_nr = nr;
> >> +
> >> +	nr /= (1024 / sizeof(void *));
> >> +	nr = 1 << (32 - __builtin_clz(nr));
> >> +	nr *= (1024 / sizeof(void *));
> >> +
> >> +	if (nr > service_fd_rlim_cur) {
> >> +		/* Right border is bigger, than rlim. OK, then just aligned value is enough */
> >> +		nr = round_down(service_fd_rlim_cur, (1024 / sizeof(void *)));
> >> +		if (nr < real_nr) {
> >> +			pr_err("Can't chose service_fd_base: %d %d\n", nr, real_nr);
> >> +			return -1;
> >> +		}
> >> +	}
> >> +
> >> +	return nr;
> >> +}
> >> +
> >>  int clone_service_fd(struct pstree_item *me)
> >>  {
> >>  	int id, new_base, i, ret = -1;
> >>  
> >> -	new_base = service_fd_base;
> >> +	new_base = choose_service_fd_base(me);
> >>  	id = rsti(me)->service_fd_id;
> >>  
> >> -	if (service_fd_id == id)
> >> +	if (new_base == -1)
> >> +		return -1;
> >> +	if (service_fd_base == new_base && service_fd_id == id)
> >>  		return 0;
> >>  
> >>  	/* Dup sfds in memmove() style: they may overlap */
> >> -	if (get_service_fd(LOG_FD_OFF) > __get_service_fd(LOG_FD_OFF, id))
> >> +	if (get_service_fd(LOG_FD_OFF) > new_base - LOG_FD_OFF - SERVICE_FD_MAX * id)
> >>  		for (i = SERVICE_FD_MIN + 1; i < SERVICE_FD_MAX; i++)
> >>  			move_service_fd(me, i, id, new_base);
> >>  	else
> >>  		for (i = SERVICE_FD_MAX - 1; i > SERVICE_FD_MIN; i--)
> >>  			move_service_fd(me, i, id, new_base);
> >>  
> >> +	service_fd_base = new_base;
> >>  	service_fd_id = id;
> >>  	ret = 0;
> >>  
> >>