linux-kernel - Re: [PATCH 2/2] ext4: Convert EXT4_B2C(sbi->s_stripe) users to EXT4_NUM

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Message-ID: <94377e74-3159-8130-df96-7955b55755c2@huaweicloud.com>
Date: Mon, 19 Aug 2024 20:51:58 +0800
From: Kemeng Shi <shikemeng@...weicloud.com>
To: Ojaswin Mujoo <ojaswin@...ux.ibm.com>, linux-ext4@...r.kernel.org,
 Theodore Ts'o <tytso@....edu>
Cc: Ritesh Harjani <ritesh.list@...il.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] ext4: Convert EXT4_B2C(sbi->s_stripe) users to
 EXT4_NUM_B2C



on 8/16/2024 3:57 PM, Ojaswin Mujoo wrote:
> Although we have checks to make sure s_stripe is a multiple of cluster
> size, in case we accidentally end up with a scenario where this is not
> the case, use EXT4_NUM_B2C() so that we don't end up with unexpected
> cases where EXT4_B2C(stripe) becomes 0.
> 
> Also make the is_stripe_aligned check in regular_allocator a bit more
> robust while we are at it. This should ideally have no functional change
> unless we have a bug somewhere causing (stripe % cluster_size != 0)
> 
> Signed-off-by: Ojaswin Mujoo <ojaswin@...ux.ibm.com>> ---
>  fs/ext4/mballoc.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> index 9dda9cd68ab2..b2e836a4bd18 100644
> --- a/fs/ext4/mballoc.c
> +++ b/fs/ext4/mballoc.c
> @@ -2553,7 +2553,7 @@ void ext4_mb_scan_aligned(struct ext4_allocation_context *ac,
>  	do_div(a, sbi->s_stripe);
>  	i = (a * sbi->s_stripe) - first_group_block;
>  
> -	stripe = EXT4_B2C(sbi, sbi->s_stripe);
> +	stripe = EXT4_NUM_B2C(sbi, sbi->s_stripe);
>  	i = EXT4_B2C(sbi, i);
>  	while (i < EXT4_CLUSTERS_PER_GROUP(sb)) {
>  		if (!mb_test_bit(i, bitmap)) {
> @@ -2929,8 +2929,9 @@ ext4_mb_regular_allocator(struct ext4_allocation_context *ac)
>  				ext4_mb_simple_scan_group(ac, &e4b);
>  			else {
>  				bool is_stripe_aligned = sbi->s_stripe &&
> +					sbi->s_stripe >= sbi->s_cluster_ratio &&
sbi->s_cluster_ratio is >= 1, so sbi->s_stripe >= sbi->s_cluster_ratio could
cover the case that sbi->s_stripe is non-zero. Non-zero check of sbi->s_stripe
seems not needed.
>  					!(ac->ac_g_ex.fe_len %
> -					  EXT4_B2C(sbi, sbi->s_stripe));
> +					  EXT4_NUM_B2C(sbi, sbi->s_stripe));
>  
>  				if ((cr == CR_GOAL_LEN_FAST ||
>  				     cr == CR_BEST_AVAIL_LEN) &&
> @@ -3707,7 +3708,7 @@ int ext4_mb_init(struct super_block *sb)
>  	 */
>  	if (sbi->s_stripe > 1) {
>  		sbi->s_mb_group_prealloc = roundup(
> -			sbi->s_mb_group_prealloc, EXT4_B2C(sbi, sbi->s_stripe));
> +			sbi->s_mb_group_prealloc, EXT4_NUM_B2C(sbi, sbi->s_stripe));
>  	}
>  
>  	sbi->s_locality_groups = alloc_percpu(struct ext4_locality_group);
>