Re: [RFC][PATCH 1/7] Resource counters

[Herbert Poetzl]

On Wed, Mar 07, 2007 at 10:19:05AM +0300, Pavel Emelianov wrote:
> Balbir Singh wrote:
> > Pavel Emelianov wrote:
> >> Introduce generic structures and routines for
> >> resource accounting.
> >>
> >> Each resource accounting container is supposed to
> >> aggregate it, container_subsystem_state and its
> >> resource-specific members within.
> >>
> >>
> >> ------------------------------------------------------------------------
> >>
> >> diff -upr linux-2.6.20.orig/include/linux/res_counter.h
> >> linux-2.6.20-0/include/linux/res_counter.h
> >> --- linux-2.6.20.orig/include/linux/res_counter.h    2007-03-06
> >> 13:39:17.000000000 +0300
> >> +++ linux-2.6.20-0/include/linux/res_counter.h    2007-03-06
> >> 13:33:28.000000000 +0300
> >> @@ -0,0 +1,83 @@
> >> +#ifndef __RES_COUNTER_H__
> >> +#define __RES_COUNTER_H__
> >> +/*
> >> + * resource counters
> >> + *
> >> + * Copyright 2007 OpenVZ SWsoft Inc
> >> + *
> >> + * Author: Pavel Emelianov <xemul@xxxxxxxxxx>
> >> + *
> >> + */
> >> +
> >> +#include <linux/container.h>
> >> +
> >> +struct res_counter {
> >> +    unsigned long usage;
> >> +    unsigned long limit;
> >> +    unsigned long failcnt;
> >> +    spinlock_t lock;
> >> +};
> >> +
> >> +enum {
> >> +    RES_USAGE,
> >> +    RES_LIMIT,
> >> +    RES_FAILCNT,
> >> +};
> >> +
> >> +ssize_t res_counter_read(struct res_counter *cnt, int member,
> >> +        const char __user *buf, size_t nbytes, loff_t *pos);
> >> +ssize_t res_counter_write(struct res_counter *cnt, int member,
> >> +        const char __user *buf, size_t nbytes, loff_t *pos);
> >> +
> >> +static inline void res_counter_init(struct res_counter *cnt)
> >> +{
> >> +    spin_lock_init(&cnt->lock);
> >> +    cnt->limit = (unsigned long)LONG_MAX;
> >> +}
> >> +
> > 
> > Is there any way to indicate that there are no limits on this container.
> 
> Yes - LONG_MAX is essentially a "no limit" value as no
> container will ever have such many files :)

-1 or ~0 is a viable choice for userspace to
communicate 'infinite' or 'unlimited'

> > LONG_MAX is quite huge, but still when the administrator wants to
> > configure a container to *un-limited usage*, it becomes hard for
> > the administrator.
> > 
> >> +static inline int res_counter_charge_locked(struct res_counter *cnt,
> >> +        unsigned long val)
> >> +{
> >> +    if (cnt->usage <= cnt->limit - val) {
> >> +        cnt->usage += val;
> >> +        return 0;
> >> +    }
> >> +
> >> +    cnt->failcnt++;
> >> +    return -ENOMEM;
> >> +}
> >> +
> >> +static inline int res_counter_charge(struct res_counter *cnt,
> >> +        unsigned long val)
> >> +{
> >> +    int ret;
> >> +    unsigned long flags;
> >> +
> >> +    spin_lock_irqsave(&cnt->lock, flags);
> >> +    ret = res_counter_charge_locked(cnt, val);
> >> +    spin_unlock_irqrestore(&cnt->lock, flags);
> >> +    return ret;
> >> +}
> >> +
> > 
> > Will atomic counters help here.
> 
> I'm afraid no. We have to atomically check for limit and alter
> one of usage or failcnt depending on the checking result. Making
> this with atomic_xxx ops will require at least two ops.

Linux-VServer does the accounting with atomic counters,
so that works quite fine, just do the checks at the
beginning of whatever resource allocation and the
accounting once the resource is acquired ...

> If we'll remove failcnt this would look like
>    while (atomic_cmpxchg(...))
> which is also not that good.
> 
> Moreover - in RSS accounting patches I perform page list
> manipulations under this lock, so this also saves one atomic op.

it still hasn't been shown that this kind of RSS limit
doesn't add big time overhead to normal operations
(inside and outside of such a resource container)

note that the 'usual' memory accounting is much more
lightweight and serves similar purposes ...

best,
Herbert

> >> +static inline void res_counter_uncharge_locked(struct res_counter *cnt,
> >> +        unsigned long val)
> >> +{
> >> +    if (unlikely(cnt->usage < val)) {
> >> +        WARN_ON(1);
> >> +        val = cnt->usage;
> >> +    }
> >> +
> >> +    cnt->usage -= val;
> >> +}
> >> +
> >> +static inline void res_counter_uncharge(struct res_counter *cnt,
> >> +        unsigned long val)
> >> +{
> >> +    unsigned long flags;
> >> +
> >> +    spin_lock_irqsave(&cnt->lock, flags);
> >> +    res_counter_uncharge_locked(cnt, val);
> >> +    spin_unlock_irqrestore(&cnt->lock, flags);
> >> +}
> >> +
> >> +#endif
> >> diff -upr linux-2.6.20.orig/init/Kconfig linux-2.6.20-0/init/Kconfig
> >> --- linux-2.6.20.orig/init/Kconfig    2007-03-06 13:33:28.000000000 +0300
> >> +++ linux-2.6.20-0/init/Kconfig    2007-03-06 13:33:28.000000000 +0300
> >> @@ -265,6 +265,10 @@ config CPUSETS
> >>
> >>        Say N if unsure.
> >>
> >> +config RESOURCE_COUNTERS
> >> +    bool
> >> +    select CONTAINERS
> >> +
> >>  config SYSFS_DEPRECATED
> >>      bool "Create deprecated sysfs files"
> >>      default y
> >> diff -upr linux-2.6.20.orig/kernel/Makefile
> >> linux-2.6.20-0/kernel/Makefile
> >> --- linux-2.6.20.orig/kernel/Makefile    2007-03-06 13:33:28.000000000
> >> +0300
> >> +++ linux-2.6.20-0/kernel/Makefile    2007-03-06 13:33:28.000000000 +0300
> >> @@ -51,6 +51,7 @@ obj-$(CONFIG_RELAY) += relay.o
> >>  obj-$(CONFIG_UTS_NS) += utsname.o
> >>  obj-$(CONFIG_TASK_DELAY_ACCT) += delayacct.o
> >>  obj-$(CONFIG_TASKSTATS) += taskstats.o tsacct.o
> >> +obj-$(CONFIG_RESOURCE_COUNTERS) += res_counter.o
> >>
> >>  ifneq ($(CONFIG_SCHED_NO_NO_OMIT_FRAME_POINTER),y)
> >>  # According to Alan Modra <alan@xxxxxxxxxxxxxxxx>, the
> >> -fno-omit-frame-pointer is
> >> diff -upr linux-2.6.20.orig/kernel/res_counter.c
> >> linux-2.6.20-0/kernel/res_counter.c
> >> --- linux-2.6.20.orig/kernel/res_counter.c    2007-03-06
> >> 13:39:17.000000000 +0300
> >> +++ linux-2.6.20-0/kernel/res_counter.c    2007-03-06
> >> 13:33:28.000000000 +0300
> >> @@ -0,0 +1,72 @@
> >> +/*
> >> + * resource containers
> >> + *
> >> + * Copyright 2007 OpenVZ SWsoft Inc
> >> + *
> >> + * Author: Pavel Emelianov <xemul@xxxxxxxxxx>
> >> + *
> >> + */
> >> +
> >> +#include <linux/parser.h>
> >> +#include <linux/fs.h>
> >> +#include <linux/res_counter.h>
> >> +#include <asm/uaccess.h>
> >> +
> >> +static inline unsigned long *res_counter_member(struct res_counter
> >> *cnt, int member)
> >> +{
> >> +    switch (member) {
> >> +    case RES_USAGE:
> >> +        return &cnt->usage;
> >> +    case RES_LIMIT:
> >> +        return &cnt->limit;
> >> +    case RES_FAILCNT:
> >> +        return &cnt->failcnt;
> >> +    };
> >> +
> >> +    BUG();
> >> +    return NULL;
> >> +}
> >> +
> >> +ssize_t res_counter_read(struct res_counter *cnt, int member,
> >> +        const char __user *userbuf, size_t nbytes, loff_t *pos)
> >> +{
> >> +    unsigned long *val;
> >> +    char buf[64], *s;
> >> +
> >> +    s = buf;
> >> +    val = res_counter_member(cnt, member);
> >> +    s += sprintf(s, "%lu\n", *val);
> >> +    return simple_read_from_buffer((void __user *)userbuf, nbytes,
> >> +            pos, buf, s - buf);
> >> +}
> >> +
> >> +ssize_t res_counter_write(struct res_counter *cnt, int member,
> >> +        const char __user *userbuf, size_t nbytes, loff_t *pos)
> >> +{
> >> +    int ret;
> >> +    char *buf, *end;
> >> +    unsigned long tmp, *val;
> >> +
> >> +    buf = kmalloc(nbytes + 1, GFP_KERNEL);
> >> +    ret = -ENOMEM;
> >> +    if (buf == NULL)
> >> +        goto out;
> >> +
> >> +    buf[nbytes] = 0;
> >> +    ret = -EFAULT;
> >> +    if (copy_from_user(buf, userbuf, nbytes))
> >> +        goto out_free;
> >> +
> >> +    ret = -EINVAL;
> >> +    tmp = simple_strtoul(buf, &end, 10);
> >> +    if (*end != '\0')
> >> +        goto out_free;
> >> +
> >> +    val = res_counter_member(cnt, member);
> >> +    *val = tmp;
> >> +    ret = nbytes;
> >> +out_free:
> >> +    kfree(buf);
> >> +out:
> >> +    return ret;
> >> +}
> >>
> > 
> > 
> > These bits look a little out of sync, with no users for these routines in
> > this patch. Won't you get a compiler warning, compiling this bit alone?
> > 
> 
> Nope - when you have a non-static function without users in a
> file no compiler warning produced.
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