linux-ext4 - Re: [PATCH v3 12/13] docs: Add fast commit documentation

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Date:   Thu, 31 Oct 2019 12:53:10 -0600
From:   Andreas Dilger <adilger@...ger.ca>
To:     "Theodore Y. Ts'o" <tytso@....EDU>
Cc:     Harshad Shirwadkar <harshadshirwadkar@...il.com>,
        linux-ext4@...r.kernel.org
Subject: Re: [PATCH v3 12/13] docs: Add fast commit documentation

On Oct 18, 2019, at 7:28 AM, Theodore Y. Ts'o <tytso@....EDU> wrote:
> 
> On Fri, Oct 18, 2019 at 01:51:56PM +0900, Andreas Dilger wrote:
>> What about rename or hard link?
> 
> Neither is currently handled by the fast commit patches, but each
> operation can fit inside a single block, so it could be handled as a
> update to a single inode.  In the case of rename, we will need to add
> some tags to indicate the desintation directory and directory enrty
> name, and whether or not there is a destination inode which needs to
> have its refcount dropped and possibly deleted.
> 
> Harshad, we probably should handle them, since in order to support
> NFS, the nfs server will send the rename or hard link request,
> followed by a commit metadata request, and that commit metadata
> request needs to persist the rename or link.  So for the purposes of
> accelerating NFS, we should handle these commands.
> 
> If we don't handle these commands, we will need to declare the inode
> as fast commit ineligible, so that we force a full journal commit when
> the commit metadata request is received.

As a simplifying assumption, you could limit the case of rename/link
within a single directory?  That handles the common case of "create
temp file, write contents there, sync, rename over original file"
used by most editors, rsync, etc.  The case of cross-directory rename
is much less common in my experience, so it is less important to
optimize that case (if this makes it easier to add to fast commits).

Cheers, Andreas






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