linux-kernel - Re: [PATCH] memblock: remove repeat round

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Date:   Mon, 24 Oct 2022 19:15:02 +0300
From:   Mike Rapoport <rppt@...nel.org>
To:     Yajun Deng <yajun.deng@...ux.dev>
Cc:     akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] memblock: remove repeat round

Hi,

On Wed, Oct 19, 2022 at 08:03:37PM +0800, Yajun Deng wrote:
> Subject: memblock: remove repeat round

Please make the patch subject more detailed. Say

membloc: don't run loop in memblock_add_range() twice

> There is no need round twice in memblock_add_range().
> 
> We can call memblock_double_array() to extand the size if type->cnt no

                                        ^ extend

> less than type->max before memblock_insert_region(), otherwise we can

s/no less than/greater or equal to/

> insert the new region directly.
> 
> Signed-off-by: Yajun Deng <yajun.deng@...ux.dev>
> ---
>  mm/memblock.c | 54 +++++++++++++++------------------------------------
>  1 file changed, 16 insertions(+), 38 deletions(-)
> 
> diff --git a/mm/memblock.c b/mm/memblock.c
> index 511d4783dcf1..1679244b4a1a 100644
> --- a/mm/memblock.c
> +++ b/mm/memblock.c
> @@ -578,7 +578,6 @@ static int __init_memblock memblock_add_range(struct memblock_type *type,
>  				phys_addr_t base, phys_addr_t size,
>  				int nid, enum memblock_flags flags)
>  {
> -	bool insert = false;
>  	phys_addr_t obase = base;
>  	phys_addr_t end = base + memblock_cap_size(base, &size);
>  	int idx, nr_new;
> @@ -598,22 +597,6 @@ static int __init_memblock memblock_add_range(struct memblock_type *type,
>  		return 0;
>  	}
>  
> -	/*
> -	 * The worst case is when new range overlaps all existing regions,
> -	 * then we'll need type->cnt + 1 empty regions in @type. So if
> -	 * type->cnt * 2 + 1 is less than type->max, we know
> -	 * that there is enough empty regions in @type, and we can insert
> -	 * regions directly.
> -	 */
> -	if (type->cnt * 2 + 1 < type->max)
> -		insert = true;
> -
> -repeat:
> -	/*
> -	 * The following is executed twice.  Once with %false @insert and
> -	 * then with %true.  The first counts the number of regions needed
> -	 * to accommodate the new area.  The second actually inserts them.
> -	 */
>  	base = obase;
>  	nr_new = 0;

I believe nr_new variable is no longer needed, is it?
  
> @@ -635,10 +618,14 @@ static int __init_memblock memblock_add_range(struct memblock_type *type,
>  #endif
>  			WARN_ON(flags != rgn->flags);
>  			nr_new++;
> -			if (insert)
> -				memblock_insert_region(type, idx++, base,
> -						       rbase - base, nid,
> -						       flags);
> +
> +			if ((type->cnt >= type->max) &&
> +			    (memblock_double_array(type, obase, size) < 0))

	if ((type->cnt >= type->max) &&
	    memblock_double_array(type, obase, size))

would be just fine.

I'd appreciate a comment above the if statement explaining when the
allocation is required.

> +				return -ENOMEM;
> +
> +			memblock_insert_region(type, idx++, base,
> +					       rbase - base, nid,
> +					       flags);
>  		}
>  		/* area below @rend is dealt with, forget about it */
>  		base = min(rend, end);
> @@ -647,28 +634,19 @@ static int __init_memblock memblock_add_range(struct memblock_type *type,
>  	/* insert the remaining portion */
>  	if (base < end) {
>  		nr_new++;
> -		if (insert)
> -			memblock_insert_region(type, idx, base, end - base,
> -					       nid, flags);
> +		if ((type->cnt >= type->max) &&
> +		    (memblock_double_array(type, obase, size) < 0))
> +			return -ENOMEM;
> +
> +		memblock_insert_region(type, idx, base, end - base,
> +				       nid, flags);
>  	}
>  
>  	if (!nr_new)
>  		return 0;
>  
> -	/*
> -	 * If this was the first round, resize array and repeat for actual
> -	 * insertions; otherwise, merge and return.
> -	 */
> -	if (!insert) {
> -		while (type->cnt + nr_new > type->max)
> -			if (memblock_double_array(type, obase, size) < 0)
> -				return -ENOMEM;
> -		insert = true;
> -		goto repeat;
> -	} else {
> -		memblock_merge_regions(type);
> -		return 0;
> -	}
> +	memblock_merge_regions(type);

A blank line here would be nice.

> +	return 0;
>  }
>  
>  /**
> -- 
> 2.25.1
> 
> 

-- 
Sincerely yours,
Mike.