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Date:   Wed, 4 Dec 2019 18:41:06 -0500
From:   "Theodore Y. Ts'o" <tytso@mit.edu>
To:     Andreas Dilger <adilger@dilger.ca>
Cc:     Daniel Phillips <daniel@phunq.net>, linux-ext4@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Subject: Re: [RFC] Thing 1: Shardmap fox Ext4
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On Wed, Dec 04, 2019 at 11:31:50AM -0700, Andreas Dilger wrote:
> One important use case that we have for Lustre that is not yet in the
> upstream ext4[*] is the ability to do parallel directory operations.
> This means we can create, lookup, and/or unlink entries in the same
> directory concurrently, to increase parallelism for large directories.
> 
> 
> [*] we've tried to submit the pdirops patch a couple of times, but the
> main blocker is that the VFS has a single directory mutex and couldn't
> use the added functionality without significant VFS changes.
> Patch at https://git.whamcloud.com/?p=fs/lustre-release.git;f=ldiskfs/kernel_patches/patches/rhel8/ext4-pdirop.patch;hb=HEAD
>

The XFS folks recently added support for parallel directory operations
into the VFS, for the benefit of XFS has this feature.  So it should
be possible adjust the patch so it will work with the upstream kernel
now.

Cheers,

					- Ted