linux-kernel - Re: [PATCH v2 2/5] huge_memory: add huge_zero_page_shrinker

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Message-ID: <762c0b08-f5a5-4e76-8203-70514de6b5c8@lucifer.local>
Date: Tue, 15 Jul 2025 15:29:08 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: "Pankaj Raghav (Samsung)" <kernel@...kajraghav.com>
Cc: Suren Baghdasaryan <surenb@...gle.com>,
        Ryan Roberts <ryan.roberts@....com>,
        Baolin Wang <baolin.wang@...ux.alibaba.com>,
        Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>, Vlastimil Babka <vbabka@...e.cz>,
        Zi Yan <ziy@...dia.com>, Mike Rapoport <rppt@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Michal Hocko <mhocko@...e.com>, David Hildenbrand <david@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>, Nico Pache <npache@...hat.com>,
        Dev Jain <dev.jain@....com>,
        "Liam R . Howlett" <Liam.Howlett@...cle.com>,
        Jens Axboe <axboe@...nel.dk>, linux-kernel@...r.kernel.org,
        willy@...radead.org, linux-mm@...ck.org, x86@...nel.org,
        linux-block@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        "Darrick J . Wong" <djwong@...nel.org>, mcgrof@...nel.org,
        gost.dev@...sung.com, hch@....de, Pankaj Raghav <p.raghav@...sung.com>
Subject: Re: [PATCH v2 2/5] huge_memory: add
 huge_zero_page_shrinker_(init|exit) function

Nit on subject, function -> functions.

On Mon, Jul 07, 2025 at 04:23:16PM +0200, Pankaj Raghav (Samsung) wrote:
> From: Pankaj Raghav <p.raghav@...sung.com>
>
> Add huge_zero_page_shrinker_init() and huge_zero_page_shrinker_exit().
> As shrinker will not be needed when static PMD zero page is enabled,
> these two functions can be a no-op.
>
> This is a preparation patch for static PMD zero page. No functional
> changes.

This is nitty stuff, but I think this is a little unclear, maybe something
like:

	We will soon be determining whether to use a shrinker depending on
	whether a static PMD zero page is available, therefore abstract out
	shrink initialisation and teardown such that we can more easily
	handle both the shrinker and static PMD zero page cases.

>
> Signed-off-by: Pankaj Raghav <p.raghav@...sung.com>

Other than nits, this LGTM, so with those addressed:

Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>

> ---
>  mm/huge_memory.c | 38 +++++++++++++++++++++++++++-----------
>  1 file changed, 27 insertions(+), 11 deletions(-)
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index d3e66136e41a..101b67ab2eb6 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -289,6 +289,24 @@ static unsigned long shrink_huge_zero_page_scan(struct shrinker *shrink,
>  }
>
>  static struct shrinker *huge_zero_page_shrinker;
> +static int huge_zero_page_shrinker_init(void)
> +{
> +	huge_zero_page_shrinker = shrinker_alloc(0, "thp-zero");
> +	if (!huge_zero_page_shrinker)
> +		return -ENOMEM;
> +
> +	huge_zero_page_shrinker->count_objects = shrink_huge_zero_page_count;
> +	huge_zero_page_shrinker->scan_objects = shrink_huge_zero_page_scan;
> +	shrinker_register(huge_zero_page_shrinker);
> +	return 0;
> +}
> +
> +static void huge_zero_page_shrinker_exit(void)
> +{
> +	shrinker_free(huge_zero_page_shrinker);
> +	return;
> +}
> +
>
>  #ifdef CONFIG_SYSFS
>  static ssize_t enabled_show(struct kobject *kobj,
> @@ -850,33 +868,31 @@ static inline void hugepage_exit_sysfs(struct kobject *hugepage_kobj)
>
>  static int __init thp_shrinker_init(void)
>  {
> -	huge_zero_page_shrinker = shrinker_alloc(0, "thp-zero");
> -	if (!huge_zero_page_shrinker)
> -		return -ENOMEM;
> +	int ret = 0;

Kinda no point in initialising to zero, unless...

>
>  	deferred_split_shrinker = shrinker_alloc(SHRINKER_NUMA_AWARE |
>  						 SHRINKER_MEMCG_AWARE |
>  						 SHRINKER_NONSLAB,
>  						 "thp-deferred_split");
> -	if (!deferred_split_shrinker) {
> -		shrinker_free(huge_zero_page_shrinker);
> +	if (!deferred_split_shrinker)
>  		return -ENOMEM;
> -	}
> -
> -	huge_zero_page_shrinker->count_objects = shrink_huge_zero_page_count;
> -	huge_zero_page_shrinker->scan_objects = shrink_huge_zero_page_scan;
> -	shrinker_register(huge_zero_page_shrinker);
>
>  	deferred_split_shrinker->count_objects = deferred_split_count;
>  	deferred_split_shrinker->scan_objects = deferred_split_scan;
>  	shrinker_register(deferred_split_shrinker);
>
> +	ret = huge_zero_page_shrinker_init();
> +	if (ret) {
> +		shrinker_free(deferred_split_shrinker);
> +		return ret;
> +	}

... you change this to:

	if (ret)
		shrinker_free(deferred_split_shrinker);

	return ret;

But it's not a big deal. Maybe I'd rename ret -> err if you keep things as
they are (but don't init to 0).

> +
>  	return 0;
>  }
>
>  static void __init thp_shrinker_exit(void)
>  {
> -	shrinker_free(huge_zero_page_shrinker);
> +	huge_zero_page_shrinker_exit();
>  	shrinker_free(deferred_split_shrinker);
>  }
>
> --
> 2.49.0
>