From: David Sterba <dsterba@suse.cz>
To: Qu Wenruo <wqu@suse.com>
Cc: linux-btrfs@vger.kernel.org
Subject: Re: [PATCH] btrfs: Add comment for BTRFS_ROOT_REF_COWS
Date: Fri, 14 Feb 2020 17:53:34 +0100 [thread overview]
Message-ID: <20200214165334.GC2902@twin.jikos.cz> (raw)
In-Reply-To: <20200212074651.33008-1-wqu@suse.com>
On Wed, Feb 12, 2020 at 03:46:51PM +0800, Qu Wenruo wrote:
> This bit is being used in too many locations while there is still no
> good enough explaination for how this bit is used.
>
> Not to mention its name really doesn't make much sense.
>
> So this patch will add my explanation on this bit, considering only
> subvolume trees, along with its reloc trees have this bit, to me it
> looks like this bit shows whether tree blocks of a root can be shared.
I think there's more tan just sharing, it should say something about
reference counted sharing. See eg. btrfs_block_can_be_shared:
864 /*
865 * Tree blocks not in reference counted trees and tree roots
866 * are never shared. If a block was allocated after the last
867 * snapshot and the block was not allocated by tree relocation,
868 * we know the block is not shared.
869 */
And there can be more specialities found when grepping for REF_COWS. The
comment explaination should be complete or at least mention what's not
documenting. The I find the suggested version insufficient but don't
have a concrete suggestions for improvement. By reading the comment and
going through code I don't feel any wiser.
next prev parent reply other threads:[~2020-02-14 16:53 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-12 7:46 [PATCH] btrfs: Add comment for BTRFS_ROOT_REF_COWS Qu Wenruo
2020-02-12 13:04 ` Josef Bacik
2020-02-14 16:53 ` David Sterba [this message]
2020-02-17 7:06 ` Qu Wenruo
2020-05-11 8:09 ` Qu Wenruo
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