From: Jeff Layton Subject: [RFC PATCH v1 00/30] fs: inode->i_version rework and optimization Date: Wed, 21 Dec 2016 12:03:17 -0500 Message-ID: <1482339827-7882-1-git-send-email-jlayton@redhat.com> Cc: linux-kernel@vger.kernel.org, linux-nfs@vger.kernel.org, linux-ext4@vger.kernel.org, linux-btrfs@vger.kernel.org, linux-xfs@vger.kernel.org To: linux-fsdevel@vger.kernel.org Return-path: Sender: linux-btrfs-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org tl;dr: I think we can greatly reduce the cost of the inode->i_version counter, by exploiting the fact that we don't need to increment it if no one is looking at it. We can also clean up the code to prepare to eventually expose this value via statx(). The inode->i_version field is supposed to be a value that changes whenever there is any data or metadata change to the inode. Some filesystems use it internally to detect directory changes during readdir. knfsd will use it if the filesystem has MS_I_VERSION set. IMA will also use it (though it's not clear to me that that works 100% -- no check for MS_I_VERSION there). Only btrfs, ext4, and xfs implement it for data changes. Because of this, these filesystems must log the inode to disk whenever the i_version counter changes. That has a non-zero performance impact, especially on write-heavy workloads, because we end up dirtying the inode metadata on every write, not just when the times change. [1] It turns out though that none of these users of i_version require that i_version change on every change to the file. The only real requirement is that it be different if _something_ changed since the last time we queried for it. [2] So, if we simply keep track of when something queries the value, we can avoid bumping the counter and that metadata update. This patchset implements this: It starts with some small cleanup patches to just remove any mention of the i_version counter in filesystems that don't actually use it. Then, we add a new set of static inlines for managing the counter. The initial version should work identically to what we have now. Then, all of the remaining filesystems that use i_version are converted to the new inlines. Once that's in place, we switch to a new implementation that allows us to track readers of i_version counter, and only bump it when it's necessary or convenient (i.e. we're going to disk anyway). The final patch switches from a scheme that uses the i_lock to serialize the counter updates during write to an atomic64_t. That's a wash performance-wise in my testing, but I like not having to take the i_lock down where it could end up nested inside other locks. With this, we reduce inode metadata updates across all 3 filesystems down to roughly the frequency of the timestamp granularity, particularly when it's not being queried (the vastly common case). The pessimal workload here is 1 byte writes, and it helps that significantly. Of course, that's not a real-world workload. A tiobench-example.fio workload also shows some modest performance gains, and I've gotten mails from the kernel test robot that show some significant performance gains on some microbenchmarks (case-msync-mt in the vm-scalability testsuite to be specific). I'm happy to run other workloads if anyone can suggest them. At this point, the patchset works and does what it's expected to do in my own testing. It seems like it's at least a modest performance win across all 3 major disk-based filesystems. It may also encourage others to implement i_version as well since it reduces that cost. Is this an avenue that's worthwhile to pursue? Note that I think we may have other changes coming in the future that will make this sort of cleanup necessary anyway. I'd like to plug in the Ceph change attribute here eventually, and that will require something like this anyway. Thoughts, comments and suggestions are welcome... --- [1]: On ext4 it must be turned on with the i_version mount option, mostly due to fears of incurring this impact, AFAICT. [2]: NFS also recommends that it appear to increase in value over time, so that clients can discard metadata updates that are older than ones they've already seen. Jeff Layton (30): lustre: don't set f_version in ll_readdir ecryptfs: remove unnecessary i_version bump ceph: remove the bump of i_version f2fs: don't bother setting i_version hpfs: don't bother with the i_version counter jfs: remove initialization of i_version counter nilfs2: remove inode->i_version initialization orangefs: remove initialization of i_version reiserfs: remove unneeded i_version bump ntfs: remove i_version handling fs: new API for handling i_version fat: convert to new i_version API affs: convert to new i_version API afs: convert to new i_version API btrfs: convert to new i_version API exofs: switch to new i_version API ext2: convert to new i_version API ext4: convert to new i_version API nfs: convert to new i_version API nfsd: convert to new i_version API ocfs2: convert to new i_version API ufs: use new i_version API xfs: convert to new i_version API IMA: switch IMA over to new i_version API fs: add a "force" parameter to inode_inc_iversion fs: only set S_VERSION when updating times if it has been queried xfs: avoid setting XFS_ILOG_CORE if i_version doesn't need incrementing btrfs: only dirty the inode in btrfs_update_time if something was changed fs: track whether the i_version has been queried with an i_state flag fs: convert i_version counter over to an atomic64_t drivers/staging/lustre/lustre/llite/dir.c | 3 - fs/affs/amigaffs.c | 4 +- fs/affs/dir.c | 4 +- fs/affs/super.c | 2 +- fs/afs/fsclient.c | 2 +- fs/afs/inode.c | 4 +- fs/btrfs/delayed-inode.c | 4 +- fs/btrfs/file.c | 4 +- fs/btrfs/inode.c | 41 ++++---- fs/btrfs/ioctl.c | 4 +- fs/btrfs/tree-log.c | 2 +- fs/btrfs/xattr.c | 2 +- fs/ceph/inode.c | 1 - fs/ecryptfs/inode.c | 1 - fs/exofs/dir.c | 8 +- fs/exofs/super.c | 2 +- fs/ext2/dir.c | 8 +- fs/ext2/super.c | 4 +- fs/ext4/dir.c | 8 +- fs/ext4/inline.c | 6 +- fs/ext4/inode.c | 16 ++-- fs/ext4/ioctl.c | 2 +- fs/ext4/namei.c | 8 +- fs/ext4/super.c | 2 +- fs/f2fs/super.c | 1 - fs/fat/dir.c | 2 +- fs/fat/inode.c | 8 +- fs/fat/namei_msdos.c | 6 +- fs/fat/namei_vfat.c | 20 ++-- fs/hpfs/dir.c | 1 - fs/hpfs/dnode.c | 2 - fs/hpfs/super.c | 1 - fs/inode.c | 9 +- fs/jfs/super.c | 1 - fs/nfs/delegation.c | 2 +- fs/nfs/fscache-index.c | 4 +- fs/nfs/inode.c | 16 ++-- fs/nfs/nfs4proc.c | 4 +- fs/nfs/nfstrace.h | 4 +- fs/nfs/write.c | 2 +- fs/nfsd/nfs3xdr.c | 2 +- fs/nfsd/nfs4xdr.c | 2 +- fs/nfsd/nfsfh.h | 2 +- fs/nilfs2/super.c | 1 - fs/ntfs/inode.c | 9 -- fs/ntfs/mft.c | 6 -- fs/ocfs2/dir.c | 14 +-- fs/ocfs2/inode.c | 2 +- fs/ocfs2/namei.c | 2 +- fs/ocfs2/quota_global.c | 2 +- fs/orangefs/super.c | 2 - fs/reiserfs/super.c | 1 - fs/ufs/dir.c | 8 +- fs/ufs/inode.c | 2 +- fs/ufs/super.c | 2 +- fs/xfs/libxfs/xfs_inode_buf.c | 4 +- fs/xfs/xfs_icache.c | 4 +- fs/xfs/xfs_inode.c | 2 +- fs/xfs/xfs_inode_item.c | 2 +- fs/xfs/xfs_trans_inode.c | 12 +-- include/linux/fs.h | 151 ++++++++++++++++++++++++++++-- security/integrity/ima/ima_api.c | 2 +- security/integrity/ima/ima_main.c | 2 +- 63 files changed, 288 insertions(+), 173 deletions(-) -- 2.7.4