linux-kernel - ext4: why init the unused block group at batched discard?

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Message-ID: <CAH9JG2Xp_u-46x8bf2Uq-9FREZyYhcP3E7H+MsSoFVrWpyLrtA@mail.gmail.com>
Date:	Wed, 6 Jul 2011 15:09:01 +0900
From:	Kyungmin Park <kmpark@...radead.org>
To:	Lukas Czerner <lczerner@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linux Filesystem Mailing List <linux-fsdevel@...r.kernel.org>
Subject: ext4: why init the unused block group at batched discard?

Hi Lukas,

During code review batched discard support at ext4. I wonder why do
you init the uninitialized block group during batched discard.
As you know uninitialized block group mean that there's no operation
at these blocks.
So no need to trim it at all.

How do you think?

int ext4_trim_fs(struct super_block *sb, struct fstrim_range *range)
{
        ...

        for (group = first_group; group <= last_group; group++) {
                grp = ext4_get_group_info(sb, group);
                /* We only do this if the grp has never been initialized */
                if (unlikely(EXT4_MB_GRP_NEED_INIT(grp))) {
                        ret = ext4_mb_init_group(sb, group);
                        if (ret)
                                break;
                }
        ...
        }
        ...
}

Thank you,
Kyungmin Park
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