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

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Date: Thu, 28 Dec 2023 11:19:08 -0800
From: Nhat Pham <nphamcs@...il.com>
To: Barry Song <21cnbao@...il.com>
Cc: minchan@...nel.org, senozhatsky@...omium.org, akpm@...ux-foundation.org, 
	linux-mm@...ck.org, ddstreet@...e.org, sjenning@...hat.com, 
	vitaly.wool@...sulko.com, linux-kernel@...r.kernel.org, chriscli@...gle.com, 
	chrisl@...nel.org, hannes@...xchg.org, yosryahmed@...gle.com, 
	zhouchengming@...edance.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 Wed, Dec 27, 2023 at 10:18 PM Barry Song <21cnbao@...il.com> 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>
> ---
>  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);
> --
> 2.34.1
>

LGTM.
Reviewed-by: Nhat Pham <nphamcs@...il.com>