On Fri, Dec 22, 2017 at 1:05 PM, Jeff Layton <jlayton@xxxxxxxxxx> wrote: > From: Jeff Layton <jlayton@xxxxxxxxxx> > > 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@xxxxxxxxxx> > --- > include/linux/fs.h | 2 +- > include/linux/iversion.h | 208 ++++++++++++++++++++++++++++++++++------------- > 2 files changed, 154 insertions(+), 56 deletions(-) > Hi, On recent linux-next my ARM/Exynos boards fail to boot over nfsroot. This commit popped up through bisect (log at the end). Systemd timeouts on some device-specific services, including mounting ext4 /home: [ *** ] (1 of 4) A start job is running for…ress polling (1min 41s / no limit) [ TIME ] Timed out waiting for device dev-ttySAC2.device. Jan 07 13:29:38 [DEPEND] Dependency failed for Serial Getty on ttySAC2. Jan 07 13:29:38 [ TIME ] Timed out waiting for device dev-disk-by\x2dlabel-home.device. Jan 07 13:29:38 [DEPEND] Dependency failed for /home. Jan 07 13:29:38 [DEPEND] Dependency failed for Local File Systems. Jan 07 13:29:38 [DEPEND] Dependency failed for File System Check on /dev/disk/by-label/home. Jan 07 13:30:02 [ *** ] (1 of 2) A start job is running for…ress polling (1min 53s / no limit) Kernel command line: console=tty1 console=ttySAC2,115200n8 ip=192.168.1.11:192.168.1.10:192.168.1.1:255.255.255.0::eth0:none nfsrootdebug root=/dev/nfs nfsroot=192.168.1.10:/srv/nfs/odroidxu3,vers=4,nolock rootwait rw smsc95xx.macaddr=00:1e:06:61:7a:93 no_console_suspend /home is /dev/mmcblk1p2: kozik@odroidxu3:~$ tune2fs -l /dev/mmcblk1p2 tune2fs 1.43.7 (16-Oct-2017) Filesystem volume name: home Last mounted on: /home Filesystem UUID: 3f9dbeba-2738-45d3-807e-c1b2e21128ed Filesystem magic number: 0xEF53 Filesystem revision #: 1 (dynamic) Filesystem features: has_journal ext_attr resize_inode dir_index filetype needs_recovery extent flex_bg sparse_super large_file uninit_bg dir_nlink extra_isize Filesystem flags: signed_directory_hash Default mount options: user_xattr acl Filesystem state: clean Errors behavior: Continue Filesystem OS type: Linux Inode count: 1430800 Block count: 5717760 Reserved block count: 285888 Free blocks: 5467576 Free inodes: 1428301 First block: 0 Block size: 4096 Fragment size: 4096 Reserved GDT blocks: 1022 Blocks per group: 32768 Fragments per group: 32768 Inodes per group: 8176 Inode blocks per group: 511 Flex block group size: 16 Filesystem created: Thu May 21 12:17:05 2015 Last mount time: Thu Dec 21 13:31:26 2017 Last write time: Thu Dec 21 13:31:26 2017 Mount count: 1 Maximum mount count: -1 Last checked: Thu Dec 21 13:31:25 2017 Check interval: 0 (<none>) Lifetime writes: 126 GB Reserved blocks uid: 0 (user root) Reserved blocks gid: 0 (group root) First inode: 11 Inode size: 256 Required extra isize: 28 Desired extra isize: 28 Journal inode: 8 Default directory hash: half_md4 Directory Hash Seed: 42e17e23-86b2-4356-ad63-78aa51651d03 Journal backup: inode blocks Full dmesg log: http://www.krzk.eu/#/builders/1/builds/1258/steps/10/logs/serial0 The regular boot from rootfs on SD card also fails - but without any serial console logs (just "Starting kernel...") so the real cause is unknown. Any hints? Best regards, Krzysztof bisect log: # bad: [73005e1a35fd67c644b0645c9e4c1efabd0fe62c] Add linux-next specific files for 20180103 # good: [30a7acd573899fd8b8ac39236eff6468b195ac7d] Linux 4.15-rc6 git bisect start 'next/master' 'next/stable' # bad: [c1d290f9ce8daa2b0a79d2fe48c1b7c3c5370f5a] Merge remote-tracking branch 'crypto/master' git bisect bad c1d290f9ce8daa2b0a79d2fe48c1b7c3c5370f5a # bad: [55695d94f0915121d106cd2d1ab94983a32f3e9a] Merge remote-tracking branch 'hid/for-next' git bisect bad 55695d94f0915121d106cd2d1ab94983a32f3e9a # good: [cffae1eead0dd91be1a3069a8348127bb00158f3] Merge remote-tracking branch 'realtek/for-next' git bisect good cffae1eead0dd91be1a3069a8348127bb00158f3 # good: [5f889f1176dc99636c6bf8af7c286decc888c007] Merge remote-tracking branch 'btrfs/next' git bisect good 5f889f1176dc99636c6bf8af7c286decc888c007 # good: [984c35877f36bee305e43a1c58176169854d85cf] Merge remote-tracking branch 'xfs/for-next' git bisect good 984c35877f36bee305e43a1c58176169854d85cf # bad: [f9fec502daea2a869232b6dff33ba3de79dd0d61] Merge remote-tracking branch 'printk/for-next' git bisect bad f9fec502daea2a869232b6dff33ba3de79dd0d61 # good: [c71d227fc4133f949dae620ed5e3a250b43f2415] make kernel-side POLL... arch-independent git bisect good c71d227fc4133f949dae620ed5e3a250b43f2415 # good: [416d20e8c31107f5dfd45d1d80d1e6c8e4871180] Merge branches 'work.get_user_pages_fast', 'work.wmci', 'work.sock_recvmsg', 'misc.netdrv', 'misc.poll', 'work.mqueue', 'work.whack-a-mole' and 'work.misc' into for-next git bisect good 416d20e8c31107f5dfd45d1d80d1e6c8e4871180 # good: [325a1de4a691512a48c1426b943a7b0b9f8d6744] xfs: convert to new i_version API git bisect good 325a1de4a691512a48c1426b943a7b0b9f8d6744 # good: [a94fe10fb114c169e7ddaecd8251521886409121] checkpatch: add pF/pf deprecation warning git bisect good a94fe10fb114c169e7ddaecd8251521886409121 # good: [6b3911dffd1184fdcd63299a5fee59ac000f2067] btrfs: only dirty the inode in btrfs_update_time if something was changed git bisect good 6b3911dffd1184fdcd63299a5fee59ac000f2067 # bad: [448f8c749a7a0ae03505823910ec45a112678048] Merge remote-tracking branch 'iversion/iversion-next' git bisect bad 448f8c749a7a0ae03505823910ec45a112678048 # bad: [8618bff776758ebff5b55211e7b5a60a0fc119a5] fs: handle inode->i_version more efficiently git bisect bad 8618bff776758ebff5b55211e7b5a60a0fc119a5 # first bad commit: [8618bff776758ebff5b55211e7b5a60a0fc119a5] fs: handle inode->i_version more efficiently
