summaryrefslogtreecommitdiff
path: root/fs
AgeCommit message (Collapse)Author
2018-05-31ovl: clean up copy-up error pathsMiklos Szeredi
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
2018-05-31ovl: return EIO on internal errorMiklos Szeredi
EIO better represents an internal error than ENOENT. Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
2018-05-31ovl: make ovl_create_real() cope with vfs_mkdir() safelyAl Viro
vfs_mkdir() may succeed and leave the dentry passed to it unhashed and negative. ovl_create_real() is the last caller breaking when that happens. [amir: split re-factoring of ovl_create_temp() to prep patch add comment about unhashed dir after mkdir add pr_warn() if mkdir succeeds and lookup fails] Signed-off-by: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: Amir Goldstein <amir73il@gmail.com> Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
2018-05-31ovl: create helper ovl_create_temp()Amir Goldstein
Also used ovl_create_temp() in ovl_create_index() instead of calling ovl_do_mkdir() directly, so now all callers of ovl_do_mkdir() are routed through ovl_create_real(), which paves the way for Al's fix for non-hashed result from vfs_mkdir(). Signed-off-by: Amir Goldstein <amir73il@gmail.com> Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
2018-05-31ovl: return dentry from ovl_create_real()Miklos Szeredi
Al Viro suggested to simplify callers of ovl_create_real() by returning the created dentry (or ERR_PTR) from ovl_create_real(). Suggested-by: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
2018-05-31ovl: struct cattr cleanupsAmir Goldstein
* Rename to ovl_cattr * Fold ovl_create_real() hardlink argument into struct ovl_cattr * Create macro OVL_CATTR() to initialize struct ovl_cattr from mode Signed-off-by: Amir Goldstein <amir73il@gmail.com> Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
2018-05-31ovl: strip debug argument from ovl_do_ helpersAmir Goldstein
It did not prove to be useful. Signed-off-by: Amir Goldstein <amir73il@gmail.com> Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
2018-05-31ovl: remove WARN_ON() real inode attributes mismatchAmir Goldstein
Overlayfs should cope with online changes to underlying layer without crashing the kernel, which is what xfstest overlay/019 checks. This test may sometimes trigger WARN_ON() in ovl_create_or_link() when linking an overlay inode that has been changed on underlying layer. Remove those WARN_ON() to prevent the stress test from failing. Signed-off-by: Amir Goldstein <amir73il@gmail.com> Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
2018-05-31ovl: Kconfig documentation fixesMiklos Szeredi
Reported-by: Randy Dunlap <rdunlap@infradead.org> Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
2018-05-30fs: clear writeback errors in inode_init_alwaysDarrick J. Wong
In inode_init_always(), we clear the inode mapping flags, which clears any retained error (AS_EIO, AS_ENOSPC) bits. Unfortunately, we do not also clear wb_err, which means that old mapping errors can leak through to new inodes. This is crucial for the XFS inode allocation path because we recycle old in-core inodes and we do not want error state from an old file to leak into the new file. This bug was discovered by running generic/036 and generic/047 in a loop and noticing that the EIOs generated by the collision of direct and buffered writes in generic/036 would survive the remount between 036 and 047, and get reported to the fsyncs (on different files!) in generic/047. Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com> Reviewed-by: Jeff Layton <jlayton@kernel.org> Reviewed-by: Brian Foster <bfoster@redhat.com>
2018-05-30smb3: add tracepoints for smb2/smb3 openSteve French
add two tracepoints for open completion. One for error one for completion (open_done). Sample output below TASK-PID CPU# |||| TIMESTAMP FUNCTION | | | |||| | | bash-15348 [007] .... 42441.027492: smb3_enter: cifs_lookup: xid=45 bash-15348 [007] .... 42441.028214: smb3_cmd_err: sid=0x6173e4ce tid=0xa05150e6 cmd=5 mid=105 status=0xc0000034 rc=-2 bash-15348 [007] .... 42441.028219: smb3_open_err: xid=45 sid=0x6173e4ce tid=0xa05150e6 cr_opts=0x0 des_access=0x80 rc=-2 bash-15348 [007] .... 42441.028225: smb3_exit_done: cifs_lookup: xid=45 fop777-24560 [002] .... 42442.627617: smb3_enter: cifs_revalidate_dentry_attr: xid=46 fop777-24560 [003] .... 42442.628301: smb3_cmd_err: sid=0x6173e4ce tid=0xa05150e6 cmd=5 mid=106 status=0xc0000034 rc=-2 fop777-24560 [003] .... 42442.628319: smb3_open_err: xid=46 sid=0x6173e4ce tid=0xa05150e6 cr_opts=0x0 des_access=0x80 rc=-2 fop777-24560 [003] .... 42442.628335: smb3_enter: cifs_atomic_open: xid=47 fop777-24560 [003] .... 42442.629587: smb3_cmd_done: sid=0x6173e4ce tid=0xa05150e6 cmd=5 mid=107 fop777-24560 [003] .... 42442.629592: smb3_open_done: xid=47 sid=0x6173e4ce tid=0xa05150e6 fid=0xb8a0984d cr_opts=0x40 des_access=0x40000080 Signed-off-by: Steve French <smfrench@gmail.com>
2018-05-30cifs: add debug output to show nocase mount optionSteve French
For smb1 nocase can be specified on mount. Allow displaying it in debug data. Signed-off-by: Steve French <smfrench@gmail.com>
2018-05-30smb3: add define for id for posix create context and corresponding structSteve French
Signed-off-by: Steve French <smfrench@gmail.com>
2018-05-30cifs: update smb2_check_message to handle PDUs without a 4 byte length headerRonnie Sahlberg
Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com> Signed-off-by: Steve French <stfrench@microsoft.com>
2018-05-30xfs: convert to bioset_init()/mempool_init()Kent Overstreet
Convert XFS to embedded bio sets. Acked-by: Darrick J. Wong <darrick.wong@oracle.com> Reviewed-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com> Signed-off-by: Jens Axboe <axboe@kernel.dk>
2018-05-30btrfs: convert to bioset_init()/mempool_init()Kent Overstreet
Convert btrfs to embedded bio sets. Acked-by: Chris Mason <clm@fb.com> Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com> Signed-off-by: Jens Axboe <axboe@kernel.dk>
2018-05-30fs: convert block_dev.c to bioset_init()Kent Overstreet
Convert block DIO code to embedded bio sets. Reviewed-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com> Signed-off-by: Jens Axboe <axboe@kernel.dk>
2018-05-30smb3: allow "posix" mount option to enable new SMB311 protocol extensionsSteve French
If "posix" (or synonym "unix" for backward compatibility) specified on mount, and server advertises support for SMB3.11 POSIX negotiate context, then enable the new posix extensions on the tcon. This can be viewed by looking for "posix" in the mount options displayed by /proc/mounts for that mount (ie if posix extensions allowed by server and the experimental POSIX extensions also requested on the mount by specifying "posix" at mount time). Also add check to warn user if conflicting unix/nounix or posix/noposix specified on mount. Signed-off-by: Steve French <smfrench@gmail.com>
2018-05-30smb3: add support for posix negotiate contextSteve French
Unlike CIFS where UNIX/POSIX extensions had been negotiatable, SMB3 did not have POSIX extensions yet. Add the new SMB3.11 POSIX negotiate context to ask the server whether it can support POSIX (and thus whether we can send the new POSIX open context). Signed-off-by: Steve French <smfrench@gmail.com>
2018-05-30cifs: allow disabling less secure legacy dialectsSteve French
To improve security it may be helpful to have additional ways to restrict the ability to override the default dialects (SMB2.1, SMB3 and SMB3.02) on mount with old dialects (CIFS/SMB1 and SMB2) since vers=1.0 (CIFS/SMB1) and vers=2.0 are weaker and less secure. Add a module parameter "disable_legacy_dialects" (/sys/module/cifs/parameters/disable_legacy_dialects) which can be set to 1 (or equivalently Y) to forbid use of vers=1.0 or vers=2.0 on mount. Also cleans up a few build warnings about globals for various module parms. Signed-off-by: Steve French <smfrench@gmail.com>
2018-05-30cifs: make minor clarifications to module params for cifs.koSteve French
Note which ones of the module params are cifs dialect only (N/A for default dialect now that has moved to SMB2.1 or later) Signed-off-by: Steve French <stfrench@microsoft.com> Reviewed-by: Ronnie Sahlberg <lsahlber@redhat.com>
2018-05-30cifs: show the "w" bit for writeable /proc/fs/cifs/* filesRonnie Sahlberg
RHBZ: 1539612 Lets show the "w" bit for those files have a .write interface to set/enable/... the feature. Reported-by: Xiaoli Feng <xifeng@redhat.com> Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com> Signed-off-by: Steve French <stfrench@microsoft.com>
2018-05-30smb3: add module alias for smb3 to cifs.koSteve French
We really don't want to be encouraging people to use the old (less secure) cifs dialect (SMB1) and it can be confusing for them with SMB3 (or later) being recommended but the module name is cifs. Add a module alias for "smb3" to cifs.ko to make this less confusing. Signed-off-by: Steve French <smfrench@gmail.com>
2018-05-30cifs: return error on invalid value written to cifsFYIRonnie Sahlberg
RHBZ: 1539617 Check that, if it is not a boolean, the value the user tries to write to /proc/fs/cifs/cifsFYI is valid and return an error if not. Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com> Signed-off-by: Steve French <stfrench@microsoft.com> Reported-by: Xiaoli Feng <xifeng@redhat.com>
2018-05-30cifs: invalidate cache when we truncate a fileRonnie Sahlberg
RHBZ: 1566345 When truncating a file we always do this synchronously to the server. Thus we need to make sure that the cached inode metadata is marked as stale so that on next getattr we will refresh the metadata. In this particular bug we want to ensure that both ctime and mtime are updated and become visible to the application after a truncate. Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com> Signed-off-by: Steve French <stfrench@microsoft.com> Reported-by: Xiaoli Feng <xifeng@redhat.com>
2018-05-30smb3: print tree id in debugdata in proc to be able to help loggingSteve French
When loooking at the logs for the new trace-cmd tracepoints for cifs, it would help to know which tid is for which share (UNC name) so update /proc/fs/cifs/DebugData to display the tid. Also display Maximal Access which was missing as well. Now the entry for typical entry for a tcon (in proc/fs/cifs/) looks like: 1) \\localhost\test Mounts: 1 DevInfo: 0x20 Attributes: 0x1006f PathComponentMax: 255 Status: 1 type: DISK Share Capabilities: None Aligned, Partition Aligned, Share Flags: 0x0 tid: 0xe0632a55 Optimal sector size: 0x200 Maximal Access: 0x1f01ff Signed-off-by: Steve French <smfrench@gmail.com>
2018-05-30smb3: add additional ftrace entry points for entry/exit to cifs.koSteve French
Signed-off-by: Steve French <smfrench@gmail.com>
2018-05-30smb3: fix various xid leaksSteve French
Fix a few cases where we were not freeing the xid which led to active requests being non-zero at unmount time. Signed-off-by: Steve French <smfrench@gmail.com> CC: Stable <stable@vger.kernel.org> Reviewed-by: Ronnie Sahlberg <lsahlber@redhat.com>
2018-05-30CIFS: Introduce offset for the 1st page in data transfer structuresLong Li
When direct I/O is used, the data buffer may not always align to page boundaries. Introduce a page offset in transport data structures to describe the location of the buffer within the page. Also change the function to pass the page offset when sending data to transport. Signed-off-by: Long Li <longli@microsoft.com> Signed-off-by: Steve French <stfrench@microsoft.com>
2018-05-30Btrfs: clean up error handling in btrfs_truncate()Omar Sandoval
btrfs_truncate() uses two variables for error handling, ret and err (if this sounds familiar, it's because btrfs_truncate_inode_items() did something similar). This is error prone, as was made evident by "Btrfs: fix error handling in btrfs_truncate()". We only have err because we don't want to mask an error if we call btrfs_update_inode() and btrfs_end_transaction(), so let's make that its own scoped return variable and use ret everywhere else. Reviewed-by: Nikolay Borisov <nborisov@suse.com> Signed-off-by: Omar Sandoval <osandov@fb.com> Signed-off-by: David Sterba <dsterba@suse.com>
2018-05-30btrfs: Factor out write portion of btrfs_get_blocks_directNikolay Borisov
Now that the read side is extracted into its own function, do the same to the write side. This leaves btrfs_get_blocks_direct_write with the sole purpose of handling common locking required. Also flip the condition in btrfs_get_blocks_direct_write so that the write case comes first and we check for if (Create) rather than if (!create). This is purely subjective but I believe makes reading a bit more "linear". No functional changes. Signed-off-by: Nikolay Borisov <nborisov@suse.com> Signed-off-by: David Sterba <dsterba@suse.com>
2018-05-30btrfs: Factor out read portion of btrfs_get_blocks_directNikolay Borisov
Currently this function handles both the READ and WRITE dio cases. This is facilitated by a bunch of 'if' statements, a goto short-circuit statement and a very perverse aliasing of "!created"(READ) case by setting lockstart = lockend and checking for lockstart < lockend for detecting the write. Let's simplify this mess by extracting the READ-only code into a separate __btrfs_get_block_direct_read function. This is only the first step, the next one will be to factor out the write side as well. The end goal will be to have the common locking/ unlocking code in btrfs_get_blocks_direct and then it will call either the read|write subvariants. No functional changes. Signed-off-by: Nikolay Borisov <nborisov@suse.com> Signed-off-by: David Sterba <dsterba@suse.com>
2018-05-30f2fs: turn down IO priority of discard from backgroundChao Yu
In order to avoid interfering normal r/w IO, let's turn down IO priority of discard issued from background. Signed-off-by: Chao Yu <yuchao0@huawei.com> Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
2018-05-30f2fs: don't split checkpoint in fstrimChao Yu
Now, we issue discard asynchronously in separated thread instead of in checkpoint, after that, we won't encounter long latency in checkpoint due to huge number of synchronous discard command handling, so, we don't need to split checkpoint to do trim in batch, merge it and obsolete related sysfs entry. Signed-off-by: Chao Yu <yuchao0@huawei.com> Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
2018-05-30f2fs: issue discard commands proactively in high fs utilizationJaegeuk Kim
In the high utilization like over 80%, we don't expect huge # of large discard commands, but do many small pending discards which affects FTL GCs a lot. Let's issue them in that case. Reviewed-by: Chao Yu <yuchao0@huawei.com> Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
2018-05-30btrfs: return ENOMEM if path allocation fails in btrfs_cross_ref_existSu Yue
The error code does not match the reason of failure and may confuse the callers. Signed-off-by: Su Yue <suy.fnst@cn.fujitsu.com> Reviewed-by: Nikolay Borisov <nborisov@suse.com> Reviewed-by: David Sterba <dsterba@suse.com> Signed-off-by: David Sterba <dsterba@suse.com>
2018-05-30btrfs: raid56: Remove VLA usageKees Cook
In the quest to remove all stack VLA usage from the kernel[1], this allocates the working buffers during regular init, instead of using stack space. This refactors the allocation code a bit to make it easier to review. [1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com Signed-off-by: Kees Cook <keescook@chromium.org> Reviewed-by: David Sterba <dsterba@suse.com> Signed-off-by: David Sterba <dsterba@suse.com>
2018-05-30xfs: repair superblocksDarrick J. Wong
If one of the backup superblocks is found to differ seriously from superblock 0, write out a fresh copy from the in-core sb. Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com> Reviewed-by: Allison Henderson <allison.henderson@oracle.com> Reviewed-by: Dave Chinner <dchinner@redhat.com>
2018-05-30xfs: add helpers to attach quotas to inodesDarrick J. Wong
Add a helper routine to attach quota information to inodes that are about to undergo repair. If that fails, we need to schedule a quotacheck for the next mount but allow the corrupted metadata repair to continue. Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com> Reviewed-by: Allison Henderson <allison.henderson@oracle.com> Reviewed-by: Dave Chinner <dchinner@redhat.com>
2018-05-30xfs: recover AG btree roots from rmap dataDarrick J. Wong
Add a helper function to help us recover btree roots from the rmap data. Callers pass in a list of rmap owner codes, buffer ops, and magic numbers. We iterate the rmap records looking for owner matches, and then read the matching blocks to see if the magic number & uuid match. If so, we then read-verify the block, and if that passes then we retain a pointer to the block with the highest level, assuming that by the end of the call we will have found the root. This will be used to reset the AGF/AGI btree root fields during their rebuild procedures. Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com> Reviewed-by: Dave Chinner <dchinner@redhat.com>
2018-05-30xfs: add helpers to dispose of old btree blocks after a repairDarrick J. Wong
Now that we've plumbed in the ability to construct a list of dead btree blocks following a repair, add more helpers to dispose of them. This is done by examining the rmapbt -- if the btree was the only owner we can free the block, otherwise it's crosslinked and we can only remove the rmapbt record. Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com> Reviewed-by: Dave Chinner <dchinner@redhat.com>
2018-05-30xfs: add helpers to collect and sift btree block pointers during repairDarrick J. Wong
Add some helpers to assemble a list of fs block extents. Generally, repair functions will iterate the rmapbt to make a list (1) of all extents owned by the nominal owner of the metadata structure; then they will iterate all other structures with the same rmap owner to make a list (2) of active blocks; and finally we have a subtraction function to subtract all the blocks in (2) from (1), with the result that (1) is now a list of blocks that were owned by the old btree and must be disposed. Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com> Reviewed-by: Dave Chinner <dchinner@redhat.com>
2018-05-30xfs: add helpers to allocate and initialize fresh btree rootsDarrick J. Wong
Add a pair of helper functions to allocate and initialize fresh btree roots. The repair functions will use these as part of recreating corrupted metadata. Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com> Reviewed-by: Dave Chinner <dchinner@redhat.com> Reviewed-by: Allison Henderson <allison.henderson@oracle.com>
2018-05-30xfs: add helpers to deal with transaction allocation and rollingDarrick J. Wong
For repairs, we need to reserve at least as many blocks as we think we're going to need to rebuild the data structure, and we're going to need some helpers to roll transactions while maintaining locks on the AG headers so that other threads cannot wander into the middle of a repair. Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com> Reviewed-by: Dave Chinner <dchinner@redhat.com> Reviewed-by: Allison Henderson <allison.henderson@oracle.com>
2018-05-30xfs: grab the per-ag structure whenever relevantDarrick J. Wong
Grab and hold the per-AG data across a scrub run whenever relevant. This helps us avoid repeated trips through rcu and the radix tree in the repair code. Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com> Reviewed-by: Dave Chinner <dchinner@redhat.com>
2018-05-30btrfs: return error value if create_io_em failed in cow_file_rangeSu Yue
In cow_file_range(), create_io_em() may fail, but its return value is not recorded. Then return value may be 0 even it failed which is a wrong behavior. Let cow_file_range() return PTR_ERR(em) if create_io_em() failed. Fixes: 6f9994dbabe5 ("Btrfs: create a helper to create em for IO") CC: stable@vger.kernel.org # 4.11+ Signed-off-by: Su Yue <suy.fnst@cn.fujitsu.com> Reviewed-by: Nikolay Borisov <nborisov@suse.com> Signed-off-by: David Sterba <dsterba@suse.com>
2018-05-30btrfs: drop useless member qgroup_reserved of btrfs_pending_snapshotGu JinXiang
Since there is no more use of qgroup_reserved member in struct btrfs_pending_snapshot, remove it. Signed-off-by: Gu JinXiang <gujx@cn.fujitsu.com> Signed-off-by: David Sterba <dsterba@suse.com>
2018-05-30btrfs: drop unused parameter qgroup_reservedGu JinXiang
Since commit 7775c8184ec0 ("btrfs: remove unused parameter from btrfs_subvolume_release_metadata") parameter qgroup_reserved is not used by caller of function btrfs_subvolume_reserve_metadata. So remove it. Signed-off-by: Gu JinXiang <gujx@cn.fujitsu.com> Reviewed-by: David Sterba <dsterba@suse.com> Signed-off-by: David Sterba <dsterba@suse.com>
2018-05-30btrfs: balance dirty metadata pages in btrfs_finish_ordered_ioEthan Lien
[Problem description and how we fix it] We should balance dirty metadata pages at the end of btrfs_finish_ordered_io, since a small, unmergeable random write can potentially produce dirty metadata which is multiple times larger than the data itself. For example, a small, unmergeable 4KiB write may produce: 16KiB dirty leaf (and possibly 16KiB dirty node) in subvolume tree 16KiB dirty leaf (and possibly 16KiB dirty node) in checksum tree 16KiB dirty leaf (and possibly 16KiB dirty node) in extent tree Although we do call balance dirty pages in write side, but in the buffered write path, most metadata are dirtied only after we reach the dirty background limit (which by far only counts dirty data pages) and wakeup the flusher thread. If there are many small, unmergeable random writes spread in a large btree, we'll find a burst of dirty pages exceeds the dirty_bytes limit after we wakeup the flusher thread - which is not what we expect. In our machine, it caused out-of-memory problem since a page cannot be dropped if it is marked dirty. Someone may worry about we may sleep in btrfs_btree_balance_dirty_nodelay, but since we do btrfs_finish_ordered_io in a separate worker, it will not stop the flusher consuming dirty pages. Also, we use different worker for metadata writeback endio, sleep in btrfs_finish_ordered_io help us throttle the size of dirty metadata pages. [Reproduce steps] To reproduce the problem, we need to do 4KiB write randomly spread in a large btree. In our 2GiB RAM machine: 1) Create 4 subvolumes. 2) Run fio on each subvolume: [global] direct=0 rw=randwrite ioengine=libaio bs=4k iodepth=16 numjobs=1 group_reporting size=128G runtime=1800 norandommap time_based randrepeat=0 3) Take snapshot on each subvolume and repeat fio on existing files. 4) Repeat step (3) until we get large btrees. In our case, by observing btrfs_root_item->bytes_used, we have 2GiB of metadata in each subvolume tree and 12GiB of metadata in extent tree. 5) Stop all fio, take snapshot again, and wait until all delayed work is completed. 6) Start all fio. Few seconds later we hit OOM when the flusher starts to work. It can be reproduced even when using nocow write. Signed-off-by: Ethan Lien <ethanlien@synology.com> Reviewed-by: David Sterba <dsterba@suse.com> [ add comment ] Signed-off-by: David Sterba <dsterba@suse.com>
2018-05-30btrfs: lift some btrfs_cross_ref_exist checks in nocow pathEthan Lien
In nocow path, we check if the extent is snapshotted in btrfs_cross_ref_exist(). We can do the similar check earlier and avoid unnecessary search into extent tree. A fio test on a Intel D-1531, 16GB RAM, SSD RAID-5 machine as follows: [global] group_reporting time_based thread=1 ioengine=libaio bs=4k iodepth=32 size=64G runtime=180 numjobs=8 rw=randwrite [file1] filename=/mnt/nocow/testfile IOPS result: unpatched patched 1 fio round: 46670 46958 snapshot 2 fio round: 51826 54498 3 fio round: 59767 61289 After snapshot, the first fio get about 5% performance gain. As we continually write to the same file, all writes will resume to nocow mode and eventually we have no performance gain. Signed-off-by: Ethan Lien <ethanlien@synology.com> Reviewed-by: David Sterba <dsterba@suse.com> [ update comments ] Signed-off-by: David Sterba <dsterba@suse.com>