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

[Minchan Kim <minchan@kernel.org>]

On Fri, Dec 19, 2014 at 02:32:44PM -0800, Andrew Morton wrote:
> On Fri, 19 Dec 2014 20:55:19 +0800 Ganesh Mahendran <opensource.ganesh@gmail.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?

Hmm, how about passing straightforward name from the user(ex, zram) when
it creates zsmalloc? (ex, ex, zs_create_pool(gfp, zram0)).
Then, we should fix debugfs_create_dir can return errno to propagate the error
to end user who can know it was failed ENOMEM or EEXIST.

> 
> > --- 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;
> > +}
> >
> > ...
> >
>