linux-kernel - Re: [PATCH] mm: zsmalloc: return -ENOSPC rather than -EINVAL in zs

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Date: Thu, 28 Dec 2023 14:23:35 +0800
From: Chengming Zhou <zhouchengming@...edance.com>
To: Barry Song <21cnbao@...il.com>, minchan@...nel.org,
 senozhatsky@...omium.org, akpm@...ux-foundation.org, linux-mm@...ck.org,
 ddstreet@...e.org, sjenning@...hat.com, vitaly.wool@...sulko.com
Cc: linux-kernel@...r.kernel.org, chriscli@...gle.com, chrisl@...nel.org,
 hannes@...xchg.org, yosryahmed@...gle.com, nphamcs@...il.com,
 Barry Song <v-songbaohua@...o.com>
Subject: Re: [PATCH] mm: zsmalloc: return -ENOSPC rather than -EINVAL in
 zs_malloc while size is too large

On 2023/12/28 14:18, Barry Song wrote:
> This is the case the "compressed" data is larger than the original data,
> it is better to return -ENOSPC which can help zswap record a poor compr
> rather than an invalid request. Then we get more friendly counting for
> reject_compress_poor in debugfs.
> 
>  bool zswap_store(struct folio *folio)
>  {
>  	...
>  	ret = zpool_malloc(zpool, dlen, gfp, &handle);
>  	if (ret == -ENOSPC) {
>  		zswap_reject_compress_poor++;
>  		goto put_dstmem;
>  	}
>  	if (ret) {
>  		zswap_reject_alloc_fail++;
>  		goto put_dstmem;
>  	}
>  	...
>  }
> 
> Also, zbud_alloc() and z3fold_alloc() are returning ENOSPC in the same
> case, eg
>  static int z3fold_alloc(struct z3fold_pool *pool, size_t size, gfp_t gfp,
>  			unsigned long *handle)
>  {
>  	...
>  	if (!size || (gfp & __GFP_HIGHMEM))
>  		return -EINVAL;
> 
>  	if (size > PAGE_SIZE)
>  		return -ENOSPC;
>  	...
>  }
> 
> Signed-off-by: Barry Song <v-songbaohua@...o.com>

Looks good to me.

Reviewed-by: Chengming Zhou <zhouchengming@...edance.com>

Thanks.

> ---
>  mm/zsmalloc.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
> index b1c0dad7f4cf..c937635e0ad1 100644
> --- a/mm/zsmalloc.c
> +++ b/mm/zsmalloc.c
> @@ -1364,9 +1364,12 @@ unsigned long zs_malloc(struct zs_pool *pool, size_t size, gfp_t gfp)
>  	int newfg;
>  	struct zspage *zspage;
>  
> -	if (unlikely(!size || size > ZS_MAX_ALLOC_SIZE))
> +	if (unlikely(!size))
>  		return (unsigned long)ERR_PTR(-EINVAL);
>  
> +	if (unlikely(size > ZS_MAX_ALLOC_SIZE))
> +		return (unsigned long)ERR_PTR(-ENOSPC);
> +
>  	handle = cache_alloc_handle(pool, gfp);
>  	if (!handle)
>  		return (unsigned long)ERR_PTR(-ENOMEM);