[Devel] Re: [PATCH 1/8] Resource counters

[Andrew Morton]

On Wed, 30 May 2007 19:26:34 +0400
Pavel Emelianov <xemul at openvz.org> 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.
> 
> Signed-off-by: Pavel Emelianov <xemul at openvz.org>
> 
> ---
> 
> diff -upr linux-2.6.22-rc2-mm1.orig/include/linux/res_counter.h linux-2.6.22-rc2-mm1-0/include/linux/res_counter.h
> --- linux-2.6.22-rc2-mm1.orig/include/linux/res_counter.h	2007-05-30 16:16:58.000000000 +0400
> +++ linux-2.6.22-rc2-mm1-0/include/linux/res_counter.h	2007-05-30 16:13:09.000000000 +0400
> @@ -0,0 +1,83 @@
> +#ifndef __RES_COUNTER_H__
> +#define __RES_COUNTER_H__
> +/*
> + * resource counters
> + *
> + * Copyright 2007 OpenVZ SWsoft Inc
> + *
> + * Author: Pavel Emelianov <xemul at openvz.org>
> + *
> + */
> +
> +#include <linux/container.h>
> +
> +struct res_counter {
> +	unsigned long usage;
> +	unsigned long limit;
> +	unsigned long failcnt;
> +	spinlock_t lock;
> +};

The one place where documentation really pays off is on data structures. 
Please document your core data structures with great care.

> +enum {
> +	RES_USAGE,
> +	RES_LIMIT,
> +	RES_FAILCNT,
> +};

Documenting these wouild be good too.

> +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;
> +}
> +
> +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;
> +}
> +
> +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);
> +}

The above functions will expand to a truly astonishing amount of code.  I
suspect they all should be uninlined.

> +#endif
> diff -upr linux-2.6.22-rc2-mm1.orig/init/Kconfig linux-2.6.22-rc2-mm1-0/init/Kconfig
> --- linux-2.6.22-rc2-mm1.orig/init/Kconfig	2007-05-30 16:13:08.000000000 +0400
> +++ linux-2.6.22-rc2-mm1-0/init/Kconfig	2007-05-30 16:13:09.000000000 +0400
> @@ -328,6 +328,10 @@ 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-2.6.22-rc2-mm1.orig/kernel/Makefile linux-2.6.22-rc2-mm1-0/kernel/Makefile
> --- linux-2.6.22-rc2-mm1.orig/kernel/Makefile	2007-05-30 16:13:08.000000000 +0400
> +++ linux-2.6.22-rc2-mm1-0/kernel/Makefile	2007-05-30 16:13:09.000000000 +0400
> @@ -56,6 +56,7 @@ obj-$(CONFIG_SYSCTL) += utsname_sysctl.o
>  obj-$(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 at linuxcare.com.au>, the -fno-omit-frame-pointer is
> diff -upr linux-2.6.22-rc2-mm1.orig/kernel/res_counter.c linux-2.6.22-rc2-mm1-0/kernel/res_counter.c
> --- linux-2.6.22-rc2-mm1.orig/kernel/res_counter.c	2007-05-30 16:16:58.000000000 +0400
> +++ linux-2.6.22-rc2-mm1-0/kernel/res_counter.c	2007-05-30 16:13:09.000000000 +0400
> @@ -0,0 +1,73 @@
> +/*
> + * resource containers
> + *
> + * Copyright 2007 OpenVZ SWsoft Inc
> + *
> + * Author: Pavel Emelianov <xemul at openvz.org>
> + *
> + */
> +
> +#include <linux/types.h>
> +#include <linux/parser.h>
> +#include <linux/fs.h>
> +#include <linux/res_counter.h>
> +#include <asm/uaccess.h>

We typically put a blank line between the linux/ includes adn the asm/
includes.

If include/linux/foo.h exists, please include that rather than
include/asm/foo.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;
> +}

You'd think that by now the kernel would have a "get a decimal number from
userspace" library function.  But I don't think we do.