linux-kernel - Re: [PATCH 4/4] nilfs2: implementation of NILFS_IOCTL_SET

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Date:	Tue, 04 Feb 2014 10:47:56 +0900 (JST)
From:	Ryusuke Konishi <konishi.ryusuke@....ntt.co.jp>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org, linux-nilfs@...r.kernel.org,
	Andreas Rohner <andreas.rohner@....net>
Subject: Re: [PATCH 4/4] nilfs2: implementation of NILFS_IOCTL_SET_SUINFO
 ioctl

On Mon, 3 Feb 2014 13:41:01 -0800, Andrew Morton wrote:
> On Tue,  4 Feb 2014 01:50:44 +0900 Ryusuke Konishi <konishi.ryusuke@....ntt.co.jp> wrote:
> 
>> With this ioctl the segment usage entries in the SUFILE can be
>> updated from userspace.
>> 
>> This is useful, because it allows the userspace GC to modify and update
>> segment usage entries for specific segments, which enables it to avoid
>> unnecessary write operations.
>> 
>> If a segment needs to be cleaned, but there is no or very little
>> reclaimable space in it, the cleaning operation basically degrades to
>> a useless moving operation. In the end the only thing that changes is
>> the location of the data and a timestamp in the segment usage
>> information. With this ioctl the GC can skip the cleaning and update
>> the segment usage entries directly instead.
>> 
>> This is basically a shortcut to cleaning the segment. It is still
>> necessary to read the segment summary information, but the writing of
>> the live blocks can be skipped if it's not worth it.
> 
> Documentation/filesystems/nilfs2.txt should be updated to document the
> new ioctl.
> 
> Which we're in there, please check that the ioctl documentation is
> otherwise complete and up-to-date.  These things have a tendency to
> bitrot.

Got it.  I missed the recent effort by Vyacheslav which added
description on every ioctl in the doucument file.

I'll send a patch for this soon.

Thanks,
Ryusuke Konishi
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