linux-kernel - Re: [PATCH v2] mm/zsmalloc: add statistics support

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Date:	Fri, 19 Dec 2014 14:32:44 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Ganesh Mahendran <opensource.ganesh@...il.com>
Cc:	minchan@...nel.org, ngupta@...are.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] mm/zsmalloc: add statistics support

On Fri, 19 Dec 2014 20:55:19 +0800 Ganesh Mahendran <opensource.ganesh@...il.com> wrote:

> Keeping fragmentation of zsmalloc in a low level is our target. But now
> we still need to add the debug code in zsmalloc to get the quantitative data.
> 
> This patch adds a new configuration CONFIG_ZSMALLOC_STAT to enable the
> statistics collection for developers. Currently only the objects statatitics
> in each class are collected. User can get the information via debugfs.
>      cat /sys/kernel/debug/zsmalloc/pool-1/...

Is everyone OK with this now?

> --- a/include/linux/zsmalloc.h
> +++ b/include/linux/zsmalloc.h
> @@ -48,4 +48,13 @@ void zs_unmap_object(struct zs_pool *pool, unsigned long handle);
>  
>  unsigned long zs_get_total_pages(struct zs_pool *pool);
>  
> +#ifdef CONFIG_ZSMALLOC_STAT
> +int get_zs_pool_index(struct zs_pool *pool);

The name is inconsistent with the rest of zsmalloc and with preferred
kernel naming conventions.  Should be "zs_get_pool_index".

> +#else
> +static inline int get_zs_pool_index(struct zs_pool *pool)
> +{
> +	return -1;
> +}
> +#endif
> +
>  #endif
> diff --git a/mm/Kconfig b/mm/Kconfig
> index 1d1ae6b..95c5728 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
>
> ...
>
> +static int zs_stats_size_show(struct seq_file *s, void *v)
> +{
> +	int i;
> +	struct zs_pool *pool = (struct zs_pool *)s->private;

The typecast is unneeded and undesirable (it defeats typechecking).

> +	struct size_class *class;
> +	int objs_per_zspage;
> +	unsigned long obj_allocated, obj_used, pages_used;
> +	unsigned long total_objs = 0, total_used_objs = 0, total_pages = 0;
> +
> +	seq_printf(s, " %5s %5s %13s %10s %10s\n", "class", "size",
> +				"obj_allocated", "obj_used", "pages_used");
> +
> +	for (i = 0; i < zs_size_classes; i++) {
> +		class = pool->size_class[i];
> +
> +		if (class->index != i)
> +			continue;
> +
> +		spin_lock(&class->lock);
> +		obj_allocated = zs_stat_get(class, OBJ_ALLOCATED);
> +		obj_used = zs_stat_get(class, OBJ_USED);
> +		spin_unlock(&class->lock);
> +
> +		objs_per_zspage = get_maxobj_per_zspage(class->size,
> +				class->pages_per_zspage);
> +		pages_used = obj_allocated / objs_per_zspage *
> +				class->pages_per_zspage;
> +
> +		seq_printf(s, " %5u %5u    %10lu %10lu %10lu\n", i,
> +			class->size, obj_allocated, obj_used, pages_used);
> +
> +		total_objs += obj_allocated;
> +		total_used_objs += obj_used;
> +		total_pages += pages_used;
> +	}
> +
> +	seq_puts(s, "\n");
> +	seq_printf(s, " %5s %5s    %10lu %10lu %10lu\n", "Total", "",
> +			total_objs, total_used_objs, total_pages);
> +
> +	return 0;
> +}
>
> ...
>
> +static int zs_pool_stat_create(struct zs_pool *pool)
> +{
> +	char name[10];

This is not good.  If the kernel creates and then destroys a pool 10000
times, zs_pool_index==10000 and we overrun the buffer.  Could use
kasprintf() in here to fix this.

zs_pool_index isn't a very good name - it doesn't index anything. 
zs_pool_id would be better.

> +	struct dentry *entry;
> +
> +	if (!zs_stat_root)
> +		return -ENODEV;
> +
> +	pool->index = atomic_inc_return(&zs_pool_index);
> +	snprintf(name, sizeof(name), "pool-%d", pool->index);
> +	entry = debugfs_create_dir(name, zs_stat_root);
> +	if (!entry) {
> +		pr_warn("pool %d, debugfs dir <%s> creation failed\n",
> +				pool->index, name);
> +		return -ENOMEM;

Sigh.  The debugfs interface does suck.  Doesn't matter much.

> +	}
> +	pool->stat_dentry = entry;
> +
> +	entry = debugfs_create_file("obj_in_classes", S_IFREG | S_IRUGO,
> +			pool->stat_dentry, pool, &zs_stat_size_ops);
> +	if (!entry) {
> +		pr_warn("pool %d, debugfs file entry <%s> creation failed\n",
> +				pool->index, "obj_in_classes");
> +		return -ENOMEM;
> +	}
> +
> +	return 0;
> +}
>
> ...
>

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