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

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Date:	Mon, 3 Feb 2014 13:41:01 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Ryusuke Konishi <konishi.ryusuke@....ntt.co.jp>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	linux-nilfs <linux-nilfs@...r.kernel.org>,
	Andreas Rohner <andreas.rohner@....net>
Subject: Re: [PATCH 4/4] nilfs2: implementation of NILFS_IOCTL_SET_SUINFO
 ioctl

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.

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