From: Dave Chinner <david@fromorbit.com>
To: Jeff Layton <jlayton@kernel.org>
Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
viro@zeniv.linux.org.uk, linux-nfs@vger.kernel.org,
bfields@fieldses.org, neilb@suse.de, jack@suse.de,
linux-ext4@vger.kernel.org, tytso@mit.edu,
adilger.kernel@dilger.ca, linux-xfs@vger.kernel.org,
darrick.wong@oracle.com, linux-btrfs@vger.kernel.org, clm@fb.com,
jbacik@fb.com, dsterba@suse.com, linux-integrity@vger.kernel.org,
zohar@linux.vnet.ibm.com, dmitry.kasatkin@gmail.com,
linux-afs@lists.infradead.org, dhowells@redhat.com,
jaltman@auristor.com, krzk@kernel.org
Subject: Re: [PATCH v5 19/19] fs: handle inode->i_version more efficiently
Date: Wed, 10 Jan 2018 09:55:56 +1100 [thread overview]
Message-ID: <20180109225556.GM16421@dastard> (raw)
In-Reply-To: <20180109141059.25929-20-jlayton@kernel.org>
On Tue, Jan 09, 2018 at 09:10:59AM -0500, Jeff Layton wrote:
> From: Jeff Layton <jlayton@redhat.com>
>
> Since i_version is mostly treated as an opaque value, we can exploit that
> fact to avoid incrementing it when no one is watching. With that change,
> we can avoid incrementing the counter on writes, unless someone has
> queried for it since it was last incremented. If the a/c/mtime don't
> change, and the i_version hasn't changed, then there's no need to dirty
> the inode metadata on a write.
>
> Convert the i_version counter to an atomic64_t, and use the lowest order
> bit to hold a flag that will tell whether anyone has queried the value
> since it was last incremented.
>
> When we go to maybe increment it, we fetch the value and check the flag
> bit. If it's clear then we don't need to do anything if the update
> isn't being forced.
>
> If we do need to update, then we increment the counter by 2, and clear
> the flag bit, and then use a CAS op to swap it into place. If that
> works, we return true. If it doesn't then do it again with the value
> that we fetch from the CAS operation.
>
> On the query side, if the flag is already set, then we just shift the
> value down by 1 bit and return it. Otherwise, we set the flag in our
> on-stack value and again use cmpxchg to swap it into place if it hasn't
> changed. If it has, then we use the value from the cmpxchg as the new
> "old" value and try again.
>
> This method allows us to avoid incrementing the counter on writes (and
> dirtying the metadata) under typical workloads. We only need to increment
> if it has been queried since it was last changed.
>
> Signed-off-by: Jeff Layton <jlayton@redhat.com>
> Reviewed-by: Jan Kara <jack@suse.cz>
Documentation helps a lot in understanding all this. Thanks for
adding it into the patch!
Acked-by: Dave Chinner <dchinner@redhat.com>
--
Dave Chinner
david@fromorbit.com
next prev parent reply other threads:[~2018-01-09 22:56 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-09 14:10 [PATCH v5 00/19] fs: rework and optimize i_version handling in filesystems Jeff Layton
2018-01-09 14:10 ` [PATCH v5 01/19] fs: new API for handling inode->i_version Jeff Layton
2018-01-18 21:38 ` J. Bruce Fields
2018-01-18 22:47 ` Jeff Layton
2018-01-09 14:10 ` [PATCH v5 02/19] fs: don't take the i_lock in inode_inc_iversion Jeff Layton
2018-01-09 15:14 ` Jan Kara
2018-01-18 21:45 ` J. Bruce Fields
2018-01-19 14:36 ` Jeff Layton
2018-01-19 14:43 ` J. Bruce Fields
2018-01-09 14:10 ` [PATCH v5 03/19] fat: convert to new i_version API Jeff Layton
2018-01-09 14:10 ` [PATCH v5 04/19] affs: " Jeff Layton
2018-01-09 14:10 ` [PATCH v5 05/19] afs: " Jeff Layton
2018-01-09 14:10 ` [PATCH v5 06/19] btrfs: " Jeff Layton
2018-01-09 14:10 ` [PATCH v5 07/19] exofs: switch " Jeff Layton
2018-01-09 14:10 ` [PATCH v5 08/19] ext2: convert " Jeff Layton
2018-01-09 14:10 ` [PATCH v5 09/19] ext4: " Jeff Layton
2018-01-09 14:10 ` [PATCH v5 10/19] nfs: " Jeff Layton
2018-01-09 14:10 ` [PATCH v5 11/19] nfsd: " Jeff Layton
2018-01-09 14:10 ` [PATCH v5 12/19] ocfs2: " Jeff Layton
2018-01-09 14:10 ` [PATCH v5 13/19] ufs: use " Jeff Layton
2018-01-09 14:10 ` [PATCH v5 14/19] xfs: convert to " Jeff Layton
2018-01-09 22:46 ` Dave Chinner
2018-01-09 14:10 ` [PATCH v5 15/19] IMA: switch IMA over " Jeff Layton
2018-01-09 14:10 ` [PATCH v5 16/19] fs: only set S_VERSION when updating times if necessary Jeff Layton
2018-01-09 14:10 ` [PATCH v5 17/19] xfs: avoid setting XFS_ILOG_CORE if i_version doesn't need incrementing Jeff Layton
2018-01-09 22:48 ` Dave Chinner
2018-01-09 14:10 ` [PATCH v5 18/19] btrfs: only dirty the inode in btrfs_update_time if something was changed Jeff Layton
2018-01-11 19:30 ` Liu Bo
2018-01-09 14:10 ` [PATCH v5 19/19] fs: handle inode->i_version more efficiently Jeff Layton
2018-01-09 22:55 ` Dave Chinner [this message]
2018-01-10 14:12 ` Krzysztof Kozlowski
2018-01-11 20:23 ` [PATCH v5 00/19] fs: rework and optimize i_version handling in filesystems Liu Bo
2018-01-12 11:49 ` Jeff Layton
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