linux-kernel - Re: [patch 2/3] mm: hugetlb_controller: convert to lockless page counters

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Date:	Tue, 7 Oct 2014 17:21:49 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	linux-mm@...ck.org, Vladimir Davydov <vdavydov@...allels.com>,
	Greg Thelen <gthelen@...gle.com>, Dave Hansen <dave@...1.net>,
	cgroups@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [patch 2/3] mm: hugetlb_controller: convert to lockless page
 counters

On Wed 24-09-14 11:43:09, Johannes Weiner wrote:
> Abandon the spinlock-protected byte counters in favor of the unlocked
> page counters in the hugetlb controller as well.
> 
> Signed-off-by: Johannes Weiner <hannes@...xchg.org>

One minor thing below:
Acked-by: Michal Hocko <mhocko@...e.cz>

[...]
>  static ssize_t hugetlb_cgroup_write(struct kernfs_open_file *of,
>  				    char *buf, size_t nbytes, loff_t off)
>  {
> -	int idx, name, ret;
> -	unsigned long long val;
> +	int ret, idx;
> +	unsigned long nr_pages;
>  	struct hugetlb_cgroup *h_cg = hugetlb_cgroup_from_css(of_css(of));
>  
> +	if (hugetlb_cgroup_is_root(h_cg)) /* Can't set limit on root */
> +		return -EINVAL;
> +
>  	buf = strstrip(buf);
> +	ret = page_counter_memparse(buf, &nr_pages);
> +	if (ret)
> +		return ret;
> +
>  	idx = MEMFILE_IDX(of_cft(of)->private);
> -	name = MEMFILE_ATTR(of_cft(of)->private);
>  
> -	switch (name) {
> +	switch (MEMFILE_ATTR(of_cft(of)->private)) {
>  	case RES_LIMIT:
> -		if (hugetlb_cgroup_is_root(h_cg)) {
> -			/* Can't set limit on root */
> -			ret = -EINVAL;
> -			break;
> -		}
> -		/* This function does all necessary parse...reuse it */
> -		ret = res_counter_memparse_write_strategy(buf, &val);
> -		if (ret)
> -			break;
> -		val = ALIGN(val, 1ULL << huge_page_shift(&hstates[idx]));
> -		ret = res_counter_set_limit(&h_cg->hugepage[idx], val);
> +		nr_pages = ALIGN(nr_pages, 1UL<<huge_page_order(&hstates[idx]));

memcg doesn't round up to the next page so I guess we do not have to do
it here as well.

> +		mutex_lock(&hugetlb_limit_mutex);
> +		ret = page_counter_limit(&h_cg->hugepage[idx], nr_pages);
> +		mutex_unlock(&hugetlb_limit_mutex);
>  		break;
>  	default:
>  		ret = -EINVAL;
[...]
-- 
Michal Hocko
SUSE Labs
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