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

[Andrei Vagin]

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?

> +	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;
>  
>