Re: [RFC][ only for review ] memory controller bacground reclaim [2/5] set/get ops for res_counter

[Pavel Emelyanov <xemul-GEFAQzZX7r8dnm+yROfE0A@public.gmane.org>]

KAMEZAWA Hiroyuki wrote:
> At implmenting high/low watermark in res_counter, it will be better to
> adjust high/low value when limit changes. (or don't allow user to specify
> high/low value)
> 
> This patch adds *internal* interface to modify resource value.
> (If there are only limit/usage/failcnt, these routines are not necessary but..)
> And will be used later.
> 
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu-+CUm20s59erQFUHtdCDX3A@public.gmane.org>
> 
>  include/linux/res_counter.h |    7 +++++++
>  kernel/res_counter.c        |   19 +++++++++++++++++++
>  2 files changed, 26 insertions(+)
> 
> Index: linux-2.6.24-rc3-mm1/include/linux/res_counter.h
> ===================================================================
> --- linux-2.6.24-rc3-mm1.orig/include/linux/res_counter.h	2007-11-28 14:18:21.000000000 +0900
> +++ linux-2.6.24-rc3-mm1/include/linux/res_counter.h	2007-11-28 14:18:33.000000000 +0900
> @@ -59,6 +59,13 @@
>  		int (*write_strategy)(char *buf, unsigned long long *val));
>  
>  /*
> + * A routine for set/get limitation value from kernel internal code.
> + * res->lock should be held before call this.
> + */
> +unsigned long long res_counter_get(struct res_counter *counter, int member);
> +void res_counter_set(struct res_counter *conter, int member,
> +			unsigned long long val);
> +/*
>   * the field descriptors. one for each member of res_counter
>   */
>  
> Index: linux-2.6.24-rc3-mm1/kernel/res_counter.c
> ===================================================================
> --- linux-2.6.24-rc3-mm1.orig/kernel/res_counter.c	2007-11-28 14:18:21.000000000 +0900
> +++ linux-2.6.24-rc3-mm1/kernel/res_counter.c	2007-11-28 14:18:33.000000000 +0900
> @@ -75,6 +75,25 @@
>  	return NULL;
>  }
>  
> +unsigned long long res_counter_get(struct res_counter *res, int member)
> +{
> +	unsigned long long *val;
> +
> +	val = res_counter_member(res, member);
> +
> +	return *val;
> +}
> +
> +void res_counter_set(struct res_counter *res, int member,
> +			unsigned long long newval)
> +{
> +	unsigned long long *val;
> +
> +	val = res_counter_member(res, member);
> +	*val = newval;

You put locking here in the res_counter_write() (patch #1). Why
is it missed here?

> +	return;
> +}
> +
>  ssize_t res_counter_read(struct res_counter *counter, int member,
>  		const char __user *userbuf, size_t nbytes, loff_t *pos,
>  		int (*read_strategy)(unsigned long long val, char *st_buf))
> 
>