linux-ext4 - Re: [PATCH v2] ext4: delete invalid ac_b_extent backup inside ext4_mb_use_best

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Message-Id: <20200813110131.A1B794C05C@d06av22.portsmouth.uk.ibm.com>
Date:   Thu, 13 Aug 2020 16:31:30 +0530
From:   Ritesh Harjani <riteshh@...ux.ibm.com>
To:     Andreas Dilger <adilger@...ger.ca>, brookxu <brookxu.cn@...il.com>
Cc:     "Theodore Ts'o" <tytso@....edu>,
        Ext4 Developers List <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH v2] ext4: delete invalid ac_b_extent backup inside
 ext4_mb_use_best_found()



On 8/13/20 2:14 PM, Andreas Dilger wrote:
> On Aug 7, 2020, at 5:32 AM, brookxu <brookxu.cn@...il.com> wrote:
>>
>> Delete invalid ac_b_extent backup inside ext4_mb_use_best_found(),
>> we have done this operation in ext4_mb_new_group_pa() and
>> ext4_mb_new_inode_pa().
> 
> I'm not sure I understand this patch completely.
> 
> The calls to ext4_mb_new_group_pa() and ext4_mb_new_inode_pa() are
> done from ext4_mb_new_preallocation(), which is called at the *end*
> of ext4_mb_use_best_found() (i.e. after the lines that are being
> deleted).
> 
> Maybe I'm confused by the description "we *have done* this operation"
> makes it seem like it was already done, but really it should be
> "we *will do* this operation in ..."?
> 
> That said, it would make more sense to keep the one line here in
> ext4_mb_use_best_found() and remove the two duplicate lines in
> ext4_mb_new_group_pa() and ext4_mb_new_inode_pa()?  In that case,
> the patch description would be more correct, like:
> 
>      Delete duplicate ac_b_extent backup in ext4_mb_new_group_pa()
>      and ext4_mb_new_inode_pa(), since we have done this operation
>      in ext4_mb_use_best_found() already.
> 

Looked into the mballoc code and I agree with Andreas points here.

-ritesh