linux-kernel - Re: [RFC PATCH 3/9] mm: zswap: refactor limit checking from zswap

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Message-ID: <88957a87-fe4c-448c-a22a-9052d65ab643@linux.dev>
Date: Wed, 27 Mar 2024 10:42:01 +0800
From: Chengming Zhou <chengming.zhou@...ux.dev>
To: Yosry Ahmed <yosryahmed@...gle.com>,
 Andrew Morton <akpm@...ux-foundation.org>
Cc: Johannes Weiner <hannes@...xchg.org>, Nhat Pham <nphamcs@...il.com>,
 linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 3/9] mm: zswap: refactor limit checking from
 zswap_store()

On 2024/3/26 07:50, Yosry Ahmed wrote:
> Refactor limit and acceptance threshold checking outside of
> zswap_store(). This code will be moved around in a following patch, so
> it would be cleaner to move a function call around.
> 
> Signed-off-by: Yosry Ahmed <yosryahmed@...gle.com>
> ---
>  mm/zswap.c | 32 ++++++++++++++++----------------
>  1 file changed, 16 insertions(+), 16 deletions(-)
> 
> diff --git a/mm/zswap.c b/mm/zswap.c
> index ff1975afb7e3d..6b890c8590ef7 100644
> --- a/mm/zswap.c
> +++ b/mm/zswap.c
> @@ -1415,6 +1415,21 @@ static void zswap_fill_page(void *ptr, unsigned long value)
>  	memset_l(page, value, PAGE_SIZE / sizeof(unsigned long));
>  }
>  
> +static bool zswap_check_limit(void)
> +{
> +	unsigned long cur_pages = zswap_total_pages();
> +	unsigned long thr = zswap_accept_thr_pages();
> +	unsigned long max_pages = zswap_max_pages();
> +
> +	if (cur_pages >= max_pages) {
> +		zswap_pool_limit_hit++;
> +		zswap_pool_reached_full = true;
> +	} else if (zswap_pool_reached_full && cur_pages <= thr) {
> +		zswap_pool_reached_full = false;
> +	}
> +	return !zswap_pool_reached_full;

nit: Then we use "!zswap_check_limit()" below, double negation looks complex,
should we change to zswap_should_reject() or something?

> +}
> +
>  bool zswap_store(struct folio *folio)
>  {
>  	swp_entry_t swp = folio->swap;
> @@ -1422,7 +1437,6 @@ bool zswap_store(struct folio *folio)
>  	struct xarray *tree = swap_zswap_tree(swp);
>  	struct obj_cgroup *objcg = NULL;
>  	struct mem_cgroup *memcg = NULL;
> -	unsigned long max_pages, cur_pages;
>  	struct zswap_entry *entry;
>  
>  	VM_WARN_ON_ONCE(!folio_test_locked(folio));
> @@ -1446,22 +1460,8 @@ bool zswap_store(struct folio *folio)
>  		mem_cgroup_put(memcg);
>  	}
>  
> -	/* Check global limits */
> -	cur_pages = zswap_total_pages();
> -	max_pages = zswap_max_pages();
> -
> -	if (cur_pages >= max_pages) {
> -		zswap_pool_limit_hit++;
> -		zswap_pool_reached_full = true;
> +	if (!zswap_check_limit())
>  		goto reject;
> -	}
> -
> -	if (zswap_pool_reached_full) {
> -		if (cur_pages > zswap_accept_thr_pages())
> -			goto reject;
> -		else
> -			zswap_pool_reached_full = false;
> -	}
>  
>  	/* allocate entry */
>  	entry = zswap_entry_cache_alloc(GFP_KERNEL, folio_nid(folio));