BC proc entries

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This page describes proc interface of [[[UBC]] subsystem.

Old interface

Old interface consisted of 2 (optionally 3) files

user_beancounters
reveals an overall information about resource consumption of each beancounter in system
user_beancounters_sub
reveals information about all beancounters and sub-beancounters in system
user_beancounters_debug
this files is shown if CONFIG_UBC_DEBUG_KMEM option is turned on and shows debugging information about each beancounter. This includes the numbers of
  1. objects charged from each slab
  2. pages charged
  3. vmalloc-ed pages
  4. page beancounters
  5. etc

New interface

In new interface only user_beancounters entry is left for compatibility with old tools. New entries reside in /proc/bc directory. This directory also contains subdirectories for each beancounter in the system. E.g.

# ls /proc/bc/
0  ioacct_debug  resources
# vzctl  start 101
...
# ls /proc/bc
0  101  ioacct_debug  resources
# ls /proc/bc/101/
ioacct  kmem_debug  resources  vmaux

All new entries that are in /proc/bc shows some overall information about BC subsystem, while entries in /proc/bc/$BCID show per-beancounter info.

Existing general entries

/proc/bc/resources
This entry looks like old user_beancounters entry but
  1. it doesn't contain “dummy” resources
  2. if new resource is added to BC it will appear in this entry only
/proc/bc/$BCID/resources
This entry shows the same as bc/resources does but for $BCID beancounter only.
/proc/bc/$BCID/vmaux
This entry shows auxiliary resources used in VM accounting.
/proc/bc/$BCID/kmem_debug
This entry is available with CONFIG_UBC_DEBUG_KMEM option set and shows per-beancounter info that was in /proc/user_beancounters_debug before.

Kernel API

Subsystems may add its own entries in /proc/bc or /proc/bc/$BCID. To facilitate this the following API is used in BC sybsystem (declared in include/ub/proc.h).

struct proc_dir_entry *bc_proc_root
This is an entry that corresponds to /proc/bc directory. If a subsystem wishes to report some information that is not per-beancounter it may create entry using this as a parent.
struct bc_proc_entry;
This describes an entry that may show per-beancounter info. This looks like this:
struct bc_proc_entry {
        char *name;
        int (*show)(struct seq_file *, void *);
        struct bc_proc_entry *next;
};
  • name is the entry name as it will appear in /proc/bc/$BCID
  • show is a callback that is to fill info about particulat beancounter
void bc_register_proc_entry(struct bc_proc_entry *);
This call registers an entry that shows per-beancounter info.

The code that fills info about BC must look like this

static int bc_my_show(struct seq_file *f, void *v)
{
        struct user_beancounter *ub;

        ub = seq_beancounter(f);
        /* dump info into f here */
        return 0;
}
...
static struct bc_proc_entry my_entry = {
        .name = "my_entry",
        .show = bc_my_show,
};

static int __init bc_my_init(void)
{
        bc_register_proc_entry(&my_entry);
        return 0;
}

late_initcall(bc_my_init);
Yellowpin.svg Note: Due to limitations in single_open the struct user_beancounter pointer is not passed as void *v into showing function but must be obtained from seq_file with seq_beancounter