linux-kernel - Re: [RFC PATCH v2 1/7] mm: zswap: add pool shrinking mechanism

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Message-ID: <20230608155847.GA352940@cmpxchg.org>
Date:   Thu, 8 Jun 2023 11:58:47 -0400
From:   Johannes Weiner <hannes@...xchg.org>
To:     Domenico Cerasuolo <cerasuolodomenico@...il.com>
Cc:     vitaly.wool@...sulko.com, minchan@...nel.org,
        senozhatsky@...omium.org, yosryahmed@...gle.com,
        linux-mm@...ck.org, ddstreet@...e.org, sjenning@...hat.com,
        nphamcs@...il.com, akpm@...ux-foundation.org,
        linux-kernel@...r.kernel.org, kernel-team@...a.com
Subject: Re: [RFC PATCH v2 1/7] mm: zswap: add pool shrinking mechanism

Hi Domenico,

Thanks for incorporating the feedback. Just two more nits:

On Tue, Jun 06, 2023 at 04:56:05PM +0200, Domenico Cerasuolo wrote:
> Each zpool driver (zbud, z3fold and zsmalloc) implements its own shrink
> function, which is called from zpool_shrink. However, with this commit,
> a unified shrink function is added to zswap. The ultimate goal is to
> eliminate the need for zpool_shrink once all zpool implementations have
> dropped their shrink code.
> 
> To ensure the functionality of each commit, this change focuses solely
> on adding the mechanism itself. No modifications are made to
> the backends, meaning that functionally, there are no immediate changes.
> The zswap mechanism will only come into effect once the backends have
> removed their shrink code. The subsequent commits will address the
> modifications needed in the backends.
> 
> Signed-off-by: Domenico Cerasuolo <cerasuolodomenico@...il.com>
> @@ -364,6 +375,12 @@ static void zswap_free_entry(struct zswap_entry *entry)
>  	if (!entry->length)
>  		atomic_dec(&zswap_same_filled_pages);
>  	else {
> +	/* zpool_evictable will be removed once all 3 backends have migrated */
> +		if (!zpool_evictable(entry->pool->zpool)) {

Comment indentation is off.

> +			spin_lock(&entry->pool->lru_lock);
> +			list_del(&entry->lru);
> +			spin_unlock(&entry->pool->lru_lock);
> +		}
>  		zpool_free(entry->pool->zpool, entry->handle);
>  		zswap_pool_put(entry->pool);
>  	}
> @@ -584,14 +601,70 @@ static struct zswap_pool *zswap_pool_find_get(char *type, char *compressor)
>  	return NULL;
>  }
>  
> +static int zswap_shrink(struct zswap_pool *pool)
> +{
> +	struct zswap_entry *lru_entry, *tree_entry = NULL;
> +	struct zswap_header *zhdr;
> +	struct zswap_tree *tree;
> +	int swpoffset;

pgoff_t

With that and what Yosry pointed out fixed, please feel free to add

Acked-by: Johannes Weiner <hannes@...xchg.org>

to the next version.