linux-ext4 - Re: [PATCH v3 3/5] ext4: call ext4_mb_mark_free_simple to free continuous bits in found chunk

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Message-ID: <20240429164648.juifmjsm7qb3d4ev@quack3>
Date: Mon, 29 Apr 2024 18:46:48 +0200
From: Jan Kara <jack@...e.cz>
To: Kemeng Shi <shikemeng@...weicloud.com>
Cc: tytso@....edu, adilger.kernel@...ger.ca, linux-ext4@...r.kernel.org,
	linux-kernel@...r.kernel.org, jack@...e.cz, ojaswin@...ux.ibm.com,
	ritesh.list@...il.com
Subject: Re: [PATCH v3 3/5] ext4: call ext4_mb_mark_free_simple to free
 continuous bits in found chunk

On Wed 24-04-24 14:19:02, Kemeng Shi wrote:
> In mb_mark_used, we will find free chunk and mark it inuse. For chunk
> in mid of passed range, we could simply mark whole chunk inuse. For chunk
> at end of range, we may need to mark a continuous bits at end of part of
> chunk inuse and keep rest part of chunk free. To only mark a part of
> chunk inuse, we firstly mark whole chunk inuse and then mark a continuous
> range at end of chunk free.
> Function mb_mark_used does several times of "mb_find_buddy; mb_clear_bit;
> ..." to mark a continuous range free which can be done by simply calling
> ext4_mb_mark_free_simple which free continuous bits in a more effective
> way.
> Just call ext4_mb_mark_free_simple in mb_mark_used to use existing and
> effective code to free continuous blocks in chunk at end of passed range.
> 
> Signed-off-by: Kemeng Shi <shikemeng@...weicloud.com>

I don't know with this patch. It looks correct to me. I don't find either
the old or the new version dramatically better so I'd say I'll leave it
upto Ted whether he finds this new version better or not...

In case Ted decides to take this patch, feel free to add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza

> ---
>  fs/ext4/mballoc.c | 38 +++++++++++++++++++++-----------------
>  1 file changed, 21 insertions(+), 17 deletions(-)
> 
> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> index a61fc52956b2..5acf413808a2 100644
> --- a/fs/ext4/mballoc.c
> +++ b/fs/ext4/mballoc.c
> @@ -2040,13 +2040,12 @@ static int mb_mark_used(struct ext4_buddy *e4b, struct ext4_free_extent *ex)
>  	int ord;
>  	int mlen = 0;
>  	int max = 0;
> -	int cur;
>  	int start = ex->fe_start;
>  	int len = ex->fe_len;
>  	unsigned ret = 0;
>  	int len0 = len;
>  	void *buddy;
> -	bool split = false;
> +	int ord_start, ord_end;
>  
>  	BUG_ON(start + len > (e4b->bd_sb->s_blocksize << 3));
>  	BUG_ON(e4b->bd_group != ex->fe_group);
> @@ -2071,16 +2070,12 @@ static int mb_mark_used(struct ext4_buddy *e4b, struct ext4_free_extent *ex)
>  
>  	/* let's maintain buddy itself */
>  	while (len) {
> -		if (!split)
> -			ord = mb_find_order_for_block(e4b, start);
> +		ord = mb_find_order_for_block(e4b, start);
>  
>  		if (((start >> ord) << ord) == start && len >= (1 << ord)) {
>  			/* the whole chunk may be allocated at once! */
>  			mlen = 1 << ord;
> -			if (!split)
> -				buddy = mb_find_buddy(e4b, ord, &max);
> -			else
> -				split = false;
> +			buddy = mb_find_buddy(e4b, ord, &max);
>  			BUG_ON((start >> ord) >= max);
>  			mb_set_bit(start >> ord, buddy);
>  			e4b->bd_info->bb_counters[ord]--;
> @@ -2094,20 +2089,29 @@ static int mb_mark_used(struct ext4_buddy *e4b, struct ext4_free_extent *ex)
>  		if (ret == 0)
>  			ret = len | (ord << 16);
>  
> -		/* we have to split large buddy */
>  		BUG_ON(ord <= 0);
>  		buddy = mb_find_buddy(e4b, ord, &max);
>  		mb_set_bit(start >> ord, buddy);
>  		e4b->bd_info->bb_counters[ord]--;
>  
> -		ord--;
> -		cur = (start >> ord) & ~1U;
> -		buddy = mb_find_buddy(e4b, ord, &max);
> -		mb_clear_bit(cur, buddy);
> -		mb_clear_bit(cur + 1, buddy);
> -		e4b->bd_info->bb_counters[ord]++;
> -		e4b->bd_info->bb_counters[ord]++;
> -		split = true;
> +		ord_start = (start >> ord) << ord;
> +		ord_end = ord_start + (1 << ord);
> +		/* first chunk */
> +		if (start > ord_start)
> +			ext4_mb_mark_free_simple(e4b->bd_sb, e4b->bd_buddy,
> +						 ord_start, start - ord_start,
> +						 e4b->bd_info);
> +
> +		/* last chunk */
> +		if (start + len < ord_end) {
> +			ext4_mb_mark_free_simple(e4b->bd_sb, e4b->bd_buddy,
> +						 start + len,
> +						 ord_end - (start + len),
> +						 e4b->bd_info);
> +			break;
> +		}
> +		len = start + len - ord_end;
> +		start = ord_end;
>  	}
>  	mb_set_largest_free_order(e4b->bd_sb, e4b->bd_info);
>  
> -- 
> 2.30.0
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR