linux-kernel - Re: [PATCH v2 01/10] maple_tree: Rework mtree_alloc

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Date:   Wed, 17 May 2023 14:17:05 -0400
From:   "Liam R. Howlett" <Liam.Howlett@...cle.com>
To:     Peng Zhang <zhangpeng.00@...edance.com>
Cc:     akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, maple-tree@...ts.infradead.org
Subject: Re: [PATCH v2 01/10] maple_tree: Rework mtree_alloc_{range,rrange}()

* Peng Zhang <zhangpeng.00@...edance.com> [230517 04:58]:
> Use mas_empty_area{_rev}() to refactor mtree_alloc_{range,rrange}()
> 
> Signed-off-by: Peng Zhang <zhangpeng.00@...edance.com>
> ---
>  lib/maple_tree.c | 63 ++++++++++++++++++++++++------------------------
>  1 file changed, 32 insertions(+), 31 deletions(-)
> 
> diff --git a/lib/maple_tree.c b/lib/maple_tree.c
> index 4eb220008f72..e1820e90f167 100644
> --- a/lib/maple_tree.c
> +++ b/lib/maple_tree.c
> @@ -6493,32 +6493,31 @@ int mtree_alloc_range(struct maple_tree *mt, unsigned long *startp,
>  {
>  	int ret = 0;
>  
> -	MA_STATE(mas, mt, min, min);
> +	MA_STATE(mas, mt, 0, 0);
>  	if (!mt_is_alloc(mt))
>  		return -EINVAL;
>  
>  	if (WARN_ON_ONCE(mt_is_reserved(entry)))
>  		return -EINVAL;
>  
> -	if (min > max)
> -		return -EINVAL;
> -
> -	if (max < size)
> -		return -EINVAL;
> -
> -	if (!size)
> -		return -EINVAL;
> -
>  	mtree_lock(mt);
>  retry:
> -	mas.offset = 0;
> -	mas.index = min;
> -	mas.last = max - size + 1;
> -	ret = mas_alloc(&mas, entry, size, startp);
> -	if (mas_nomem(&mas, gfp))
> -		goto retry;
> -
> +	ret = mas_empty_area(&mas, min, max, size);
> +	if (!ret) {
> +		mas_insert(&mas, entry);
> +		/*
> +		 * mas_nomem() may release the lock, causing the allocated area
> +		 * to be unavailable, so try to allocate a free area again.
> +		 */
> +		if (mas_nomem(&mas, gfp))
> +			goto retry;
> +	}
>  	mtree_unlock(mt);
> +	if (!ret) {

Checking for a mas_is_err() should probably be outside if (!ret)
statement.  If mas_insert() returns something besides ENOMEM, we will
not detect the error.  I'm not sure if this is possible today since this
should never return an -EEXISTS, but having it this way doesn't add much
to the overhead.

> +		if (mas_is_err(&mas))
> +			return xa_err(mas.node);
> +		*startp = mas.index;
> +	}
>  	return ret;
>  }
>  EXPORT_SYMBOL(mtree_alloc_range);
> @@ -6529,29 +6528,31 @@ int mtree_alloc_rrange(struct maple_tree *mt, unsigned long *startp,
>  {
>  	int ret = 0;
>  
> -	MA_STATE(mas, mt, min, max - size + 1);
> +	MA_STATE(mas, mt, 0, 0);
>  	if (!mt_is_alloc(mt))
>  		return -EINVAL;
>  
>  	if (WARN_ON_ONCE(mt_is_reserved(entry)))
>  		return -EINVAL;
>  
> -	if (min > max)
> -		return -EINVAL;
> -
> -	if (max < size - 1)
> -		return -EINVAL;
> -
> -	if (!size)
> -		return -EINVAL;
> -
>  	mtree_lock(mt);
>  retry:
> -	ret = mas_rev_alloc(&mas, min, max, entry, size, startp);
> -	if (mas_nomem(&mas, gfp))
> -		goto retry;
> -
> +	ret = mas_empty_area_rev(&mas, min, max, size);
> +	if (!ret) {
> +		mas_insert(&mas, entry);
> +		/*
> +		 * mas_nomem() may release the lock, causing the allocated area
> +		 * to be unavailable, so try to allocate a free area again.
> +		 */
> +		if (mas_nomem(&mas, gfp))
> +			goto retry;
> +	}
>  	mtree_unlock(mt);
> +	if (!ret) {

Same here.

> +		if (mas_is_err(&mas))
> +			return xa_err(mas.node);
> +		*startp = mas.index;
> +	}
>  	return ret;
>  }
>  EXPORT_SYMBOL(mtree_alloc_rrange);
> -- 
> 2.20.1
>