linux-kernel - Re: [PATCH] ext4: Replace CR_FAST macro with inline function for readability

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Message-ID: <ZJ2YIr5EVbz4ezIc@li-bb2b2a4c-3307-11b2-a85c-8fa5c3a69313.ibm.com>
Date:   Thu, 29 Jun 2023 20:11:38 +0530
From:   Ojaswin Mujoo <ojaswin@...ux.ibm.com>
To:     Jan Kara <jack@...e.cz>
Cc:     linux-ext4@...r.kernel.org, "Theodore Ts'o" <tytso@....edu>,
        Ritesh Harjani <riteshh@...ux.ibm.com>,
        linux-kernel@...r.kernel.org,
        Kemeng Shi <shikemeng@...weicloud.com>
Subject: Re: [PATCH] ext4: Replace CR_FAST macro with inline function for
 readability

On Thu, Jun 29, 2023 at 04:00:18PM +0200, Jan Kara wrote:
> On Thu 29-06-23 19:17:19, Ojaswin Mujoo wrote:
> > Replace CR_FAST with ext4_mb_cr_expensive() inline function for better
> > readability. This function returns true if the criteria is one of the
> > expensive/slower ones where lots of disk IO/prefetching is acceptable.
> > 
> > No functional changes are intended in this patch.
> > 
> > Signed-off-by: Ojaswin Mujoo <ojaswin@...ux.ibm.com>
> 
> Thanks for this cleanup! Feel free to add:
> 
> Reviewed-by: Jan Kara <jack@...e.cz>
> 
> Just one suggestion for consideration below:
> 
> > @@ -2630,7 +2630,7 @@ static int ext4_mb_good_group_nolock(struct ext4_allocation_context *ac,
> >  	free = grp->bb_free;
> >  	if (free == 0)
> >  		goto out;
> > -	if (cr <= CR_FAST && free < ac->ac_g_ex.fe_len)
> > +	if (cr <= CR_GOAL_LEN_SLOW && free < ac->ac_g_ex.fe_len)
> 
> Maybe this could be (!ext4_mb_cr_expensive(cr) || cr == CR_GOAL_LEN_SLOW)?
> Or maybe more explanatory would be (cr < CR_ANY_FREE) because AFAIU that's
> the only scan where we bother scanning groups that have no chance of
> satisfying the full allocation? Anyway a short comment explaining this
> might be useful. And in either case we can get rid of a bit confusing
> CR_FAST define.
> 
> 								Honza

Thanks for the review Jan! I actually had the same idea since it 
felt like (cr <= CR_GOAL_LEN_SLOW) doesnt clearly express the intent of this
check. I think I ultimately decided to leave it untouched to keep things
simple.

However, I like the idea of making it (cr < CR_ANY_FREE) with a comment
to explain the intent behind this condition. If it's fine with everyone I can
address it in v2.

Regards,
ojaswin
> -- 
> Jan Kara <jack@...e.com>
> SUSE Labs, CR