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

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Message-ID: <ZsQ30gFzp0IB/AGD@li-bb2b2a4c-3307-11b2-a85c-8fa5c3a69313.ibm.com>
Date: Tue, 20 Aug 2024 11:59:38 +0530
From: Ojaswin Mujoo <ojaswin@...ux.ibm.com>
To: Kemeng Shi <shikemeng@...weicloud.com>
Cc: linux-ext4@...r.kernel.org, "Theodore Ts'o" <tytso@....edu>,
        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 Mon, Aug 19, 2024 at 08:51:58PM +0800, Kemeng Shi wrote:
> 
> 
> 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.

That makes sense Kemeng, I'll send a v2 with this change.

Thanks,
ojaswin

> >  					!(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);
> > 
>