Re: [-mm PATCH] Memory controller improve user interface

["Paul Menage" <menage@google.com>]

On 8/29/07, Balbir Singh <balbir@linux.vnet.ibm.com> wrote:
>
> Change the interface to use kilobytes instead of pages. Page sizes can vary
> across platforms and configurations. A new strategy routine has been added
> to the resource counters infrastructure to format the data as desired.
>
> Suggested by David Rientjes, Andrew Morton and Herbert Poetzl
>
> Signed-off-by: Balbir Singh <balbir@linux.vnet.ibm.com>
> ---
>
>  Documentation/controllers/memory.txt |    7 +++--
>  include/linux/res_counter.h          |    6 ++--
>  kernel/res_counter.c                 |   24 +++++++++++++----
>  mm/memcontrol.c                      |   47 +++++++++++++++++++++++++++--------
>  4 files changed, 64 insertions(+), 20 deletions(-)
>
> diff -puN mm/memcontrol.c~mem-control-make-ui-use-kilobytes mm/memcontrol.c
> --- linux-2.6.23-rc3/mm/memcontrol.c~mem-control-make-ui-use-kilobytes  2007-08-28 13:20:44.000000000 +0530
> +++ linux-2.6.23-rc3-balbir/mm/memcontrol.c     2007-08-29 14:36:07.000000000 +0530
> @@ -32,6 +32,7 @@
>
>  struct container_subsys mem_container_subsys;
>  static const int MEM_CONTAINER_RECLAIM_RETRIES = 5;
> +static const int MEM_CONTAINER_CHARGE_KB = (PAGE_SIZE >> 10);
>
>  /*
>   * The memory controller data structure. The memory controller controls both
> @@ -312,7 +313,7 @@ int mem_container_charge(struct page *pa
>          * If we created the page_container, we should free it on exceeding
>          * the container limit.
>          */
> -       while (res_counter_charge(&mem->res, 1)) {
> +       while (res_counter_charge(&mem->res, MEM_CONTAINER_CHARGE_KB)) {
>                 if (try_to_free_mem_container_pages(mem))
>                         continue;
>
> @@ -352,7 +353,7 @@ int mem_container_charge(struct page *pa
>                 kfree(pc);
>                 pc = race_pc;
>                 atomic_inc(&pc->ref_cnt);
> -               res_counter_uncharge(&mem->res, 1);
> +               res_counter_uncharge(&mem->res, MEM_CONTAINER_CHARGE_KB);
>                 css_put(&mem->css);
>                 goto done;
>         }
> @@ -417,7 +418,7 @@ void mem_container_uncharge(struct page_
>                 css_put(&mem->css);
>                 page_assign_page_container(page, NULL);
>                 unlock_page_container(page);
> -               res_counter_uncharge(&mem->res, 1);
> +               res_counter_uncharge(&mem->res, MEM_CONTAINER_CHARGE_KB);
>
>                 spin_lock_irqsave(&mem->lru_lock, flags);
>                 list_del_init(&pc->lru);
> @@ -426,12 +427,37 @@ void mem_container_uncharge(struct page_
>         }
>  }
>
> -static ssize_t mem_container_read(struct container *cont, struct cftype *cft,
> -                       struct file *file, char __user *userbuf, size_t nbytes,
> -                       loff_t *ppos)
> +int mem_container_read_strategy(unsigned long val, char *buf)
> +{
> +       return sprintf(buf, "%lu (kB)\n", val);
> +}
> +
> +int mem_container_write_strategy(char *buf, unsigned long *tmp)
> +{
> +       *tmp = memparse(buf, &buf);
> +       if (*buf != '\0')
> +               return -EINVAL;
> +
> +       *tmp = *tmp >> 10;              /* convert to kilobytes */
> +       return 0;
> +}

This seems a bit inconsistent - if you write a value to a limit file,
then the value that you read back is reduced by a factor of 1024?
Having the "(kB)" suffix isn't really a big help to automated
middleware.

I'd still be in favour of just reading/writing 64-bit values
representing bytes - simple, and unambiguous for programmatic use, and
not really any less user-friendly than kilobytes  for manual use
(since the numbers involved are going to be unwieldly for manual use
whether they're in bytes or kB).

Paul

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