Even though the length of the critical section when adding / removing
orphaned inodes was significantly reduced by using orphan file, the
contention of lock protecting orphan file still appears high in profiles
for truncate / unlink intensive workloads with high number of threads.
This patch makes handling of orphan file completely lockless. Also to
reduce conflicts between CPUs different CPUs start searching for empty
slot in orphan file in different blocks.
Performance comparison of locked orphan file handling, lockless orphan
file handling, and completely disabled orphan inode handling
from 80 CPU Xeon Server with 526 GB of RAM, filesystem located on
SAS SSD disk, average of 5 runs:
stress-orphan (microbenchmark truncating files byte-by-byte from N
processes in parallel)
Threads Time Time Time
Orphan locked Orphan lockless No orphan
1 0.945600 0.939400 0.891200
2 1.331800 1.246600 1.174400
4 1.995000 1.780600 1.713200
8 6.424200 4.900000 4.106000
16 14.937600 8.516400 8.138000
32 33.038200 24.565600 24.002200
64 60.823600 39.844600 38.440200
128 122.941400 70.950400 69.315000
So we can see that with lockless orphan file handling, addition /
deletion of orphaned inodes got almost completely out of picture even
for a microbenchmark stressing it.
For reaim creat_clo workload on ramdisk there are also noticeable gains
(average of 5 runs):
Clients Vanilla (ops/s) Patched (ops/s)
creat_clo-1 14705.88 ( 0.00%) 14354.07 * -2.39%*
creat_clo-3 27108.43 ( 0.00%) 28301.89 ( 4.40%)
creat_clo-5 37406.48 ( 0.00%) 45180.73 * 20.78%*
creat_clo-7 41338.58 ( 0.00%) 54687.50 * 32.29%*
creat_clo-9 45226.13 ( 0.00%) 62937.07 * 39.16%*
creat_clo-11 44000.00 ( 0.00%) 65088.76 * 47.93%*
creat_clo-13 36516.85 ( 0.00%) 68661.97 * 88.03%*
creat_clo-15 30864.20 ( 0.00%) 69551.78 * 125.35%*
creat_clo-17 27478.45 ( 0.00%) 67729.08 * 146.48%*
creat_clo-19 25000.00 ( 0.00%) 61621.62 * 146.49%*
creat_clo-21 18772.35 ( 0.00%) 63829.79 * 240.02%*
creat_clo-23 16698.94 ( 0.00%) 61938.96 * 270.92%*
creat_clo-25 14973.05 ( 0.00%) 56947.61 * 280.33%*
creat_clo-27 16436.69 ( 0.00%) 65008.03 * 295.51%*
creat_clo-29 13949.01 ( 0.00%) 69047.62 * 395.00%*
creat_clo-31 14283.52 ( 0.00%) 67982.45 * 375.95%*
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Lukas Czerner <lczerner@redhat.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20210816095713.16537-5-jack@suse.cz
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Ext4 orphan inode handling is a bottleneck for workloads which heavily
truncate / unlink small files since it contends on the global
s_orphan_mutex lock (and generally it's difficult to improve scalability
of the ondisk linked list of orphaned inodes).
This patch implements new way of handling orphan inodes. Instead of
linking orphaned inode into a linked list, we store it's inode number in
a new special file which we call "orphan file". Only if there's no more
space in the orphan file (too many inodes are currently orphaned) we
fall back to using old style linked list. Currently we protect
operations in the orphan file with a spinlock for simplicity but even in
this setting we can substantially reduce the length of the critical
section and thus speedup some workloads. In the next patch we improve
this by making orphan handling lockless.
Note that the change is backwards compatible when the filesystem is
clean - the existence of the orphan file is a compat feature, we set
another ro-compat feature indicating orphan file needs scanning for
orphaned inodes when mounting filesystem read-write. This ro-compat
feature gets cleared on unmount / remount read-only.
Some performance data from 80 CPU Xeon Server with 512 GB of RAM,
filesystem located on SSD, average of 5 runs:
stress-orphan (microbenchmark truncating files byte-by-byte from N
processes in parallel)
Threads Time Time
Vanilla Patched
1 1.057200 0.945600
2 1.680400 1.331800
4 2.547000 1.995000
8 7.049400 6.424200
16 14.827800 14.937600
32 40.948200 33.038200
64 87.787400 60.823600
128 206.504000 122.941400
So we can see significant wins all over the board.
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20210816095713.16537-3-jack@suse.cz
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
JBD2 layer support triggers which are called when journaling layer moves
buffer to a certain state. We can use the frozen trigger, which gets
called when buffer data is frozen and about to be written out to the
journal, to compute block checksums for some buffer types (similarly as
does ocfs2). This avoids unnecessary repeated recomputation of the
checksum (at the cost of larger window where memory corruption won't be
caught by checksumming) and is even necessary when there are
unsynchronized updaters of the checksummed data.
So add superblock and journal trigger type arguments to
ext4_journal_get_write_access() and ext4_journal_get_create_access() so
that frozen triggers can be set accordingly. Also add inode argument to
ext4_walk_page_buffers() and all the callbacks used with that function
for the same purpose. This patch is mostly only a change of prototype of
the above mentioned functions and a few small helpers. Real checksumming
will come later.
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20210816095713.16537-1-jack@suse.cz
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Add sparse annotations to suppress false positive context imbalance
warnings, and use NULL instead of 0 in EXT_MAX_{EXTENT,INDEX}.
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
The location of the system.data extended attribute can change whenever
xattr_sem is not taken. So we need to recalculate the i_inline_off
field since it mgiht have changed between ext4_write_begin() and
ext4_write_end().
This means that caching i_inline_off is probably not helpful, so in
the long run we should probably get rid of it and shrink the in-memory
ext4 inode slightly, but let's fix the race the simple way for now.
Cc: stable@kernel.org
Fixes: f19d5870cb ("ext4: add normal write support for inline data")
Reported-by: syzbot+13146364637c7363a7de@syzkaller.appspotmail.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
If ext4 filesystem is corrupted so that quota files are linked from
directory hirerarchy, bad things can happen. E.g. quota files can get
corrupted or deleted. Make sure we are not grabbing quota file inodes
when we expect normal inodes.
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Link: https://lore.kernel.org/r/20210812133122.26360-1-jack@suse.cz
Commit 81414b4dd4 ("ext4: remove redundant sb checksum
recomputation") removed checksum recalculation after updating
superblock free space / inode counters in ext4_fill_super() based on
the fact that we will recalculate the checksum on superblock
writeout.
That is correct assumption but until the writeout happens (which can
take a long time) the checksum is incorrect in the buffer cache and if
programs such as tune2fs or resize2fs is called shortly after a file
system is mounted can fail. So return back the checksum recalculation
and add a comment explaining why.
Fixes: 81414b4dd4 ("ext4: remove redundant sb checksum recomputation")
Cc: stable@kernel.org
Reported-by: Boyang Xue <bxue@redhat.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Link: https://lore.kernel.org/r/20210812124737.21981-1-jack@suse.cz
If the underlying storage device is using thin-provisioning, it's
possible for a zeroout operation to return ENOSPC.
Commit df22291ff0 ("ext4: Retry block allocation if we have free blocks
left") added logic to retry block allocation since we might get free block
after we commit a transaction. But the ENOSPC from thin-provisioning
will confuse ext4, and lead to an infinite loop.
Since using zeroout instead of splitting the extent node is an
optimization, if it fails, we might as well fall back to splitting the
extent node.
Reported-by: yangerkun <yangerkun@huawei.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
The background discard kwork tries to mark blocks used and issue
discard. This can make filesystem suffer from NOSPC error, xfstest
generic/371 can fail due to it. Fix it by flushing discard kwork
in ext4_should_retry_alloc. At the same time, give up discard at
the moment.
Signed-off-by: Wang Jianchao <wangjianchao@kuaishou.com>
Link: https://lore.kernel.org/r/20210830075246.12516-6-jianchao.wan9@gmail.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Right now, discard is issued and waited to be completed in jbd2
commit kthread context after the logs are committed. When large
amount of files are deleted and discard is flooding, jbd2 commit
kthread can be blocked for long time. Then all of the metadata
operations can be blocked to wait the log space.
One case is the page fault path with read mm->mmap_sem held, which
wants to update the file time but has to wait for the log space.
When other threads in the task wants to do mmap, then write mmap_sem
is blocked. Finally all of the following read mmap_sem requirements
are blocked, even the ps command which need to read the /proc/pid/
-cmdline. Our monitor service which needs to read /proc/pid/cmdline
used to be blocked for 5 mins.
This patch frees the blocks back to buddy after commit and then do
discard in a async kworker context in fstrim fashion, namely,
- mark blocks to be discarded as used if they have not been allocated
- do discard
- mark them free
After this, jbd2 commit kthread won't be blocked any more by discard
and we won't get NOSPC even if the discard is slow or throttled.
Link: https://marc.info/?l=linux-kernel&m=162143690731901&w=2
Suggested-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Wang Jianchao <wangjianchao@kuaishou.com>
Link: https://lore.kernel.org/r/20210830075246.12516-5-jianchao.wan9@gmail.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Pull fs hole punching vs cache filling race fixes from Jan Kara:
"Fix races leading to possible data corruption or stale data exposure
in multiple filesystems when hole punching races with operations such
as readahead.
This is the series I was sending for the last merge window but with
your objection fixed - now filemap_fault() has been modified to take
invalidate_lock only when we need to create new page in the page cache
and / or bring it uptodate"
* tag 'hole_punch_for_v5.15-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/jack/linux-fs:
filesystems/locking: fix Malformed table warning
cifs: Fix race between hole punch and page fault
ceph: Fix race between hole punch and page fault
fuse: Convert to using invalidate_lock
f2fs: Convert to using invalidate_lock
zonefs: Convert to using invalidate_lock
xfs: Convert double locking of MMAPLOCK to use VFS helpers
xfs: Convert to use invalidate_lock
xfs: Refactor xfs_isilocked()
ext2: Convert to using invalidate_lock
ext4: Convert to use mapping->invalidate_lock
mm: Add functions to lock invalidate_lock for two mappings
mm: Protect operations adding pages to page cache with invalidate_lock
documentation: Sync file_operations members with reality
mm: Fix comments mentioning i_mutex
Add a rcu argument to the ->get_acl() callback to allow
get_cached_acl_rcu() to call the ->get_acl() method in the next patch.
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Commit b5776e7524 ("ext4: fix potential htree index checksum
corruption) removed a required restart when multiple levels of index
nodes need to be split. Fix this to avoid directory htree corruptions
when using the large_dir feature.
Cc: stable@kernel.org # v5.11
Cc: Благодаренко Артём <artem.blagodarenko@gmail.com>
Fixes: b5776e7524 ("ext4: fix potential htree index checksum corruption)
Reported-by: Denis <denis@voxelsoft.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
The stat() family of syscalls report the wrong size for encrypted
symlinks, which has caused breakage in several userspace programs.
Fix this by calling fscrypt_symlink_getattr() after ext4_getattr() for
encrypted symlinks. This function computes the correct size by reading
and decrypting the symlink target (if it's not already cached).
For more details, see the commit which added fscrypt_symlink_getattr().
Fixes: f348c25232 ("ext4 crypto: add symlink encryption")
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20210702065350.209646-3-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
Convert ext4 to use mapping->invalidate_lock instead of its private
EXT4_I(inode)->i_mmap_sem. This is mostly search-and-replace. By this
conversion we fix a long standing race between hole punching and read(2)
/ readahead(2) paths that can lead to stale page cache contents.
CC: <linux-ext4@vger.kernel.org>
CC: Ted Tso <tytso@mit.edu>
Acked-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Jan Kara <jack@suse.cz>
Pull ext4 updates from Ted Ts'o:
"Ext4 regression and bug fixes"
* tag 'ext4_for_linus_stable' of git://git.kernel.org/pub/scm/linux/kernel/git/tytso/ext4:
ext4: inline jbd2_journal_[un]register_shrinker()
ext4: fix flags validity checking for EXT4_IOC_CHECKPOINT
ext4: fix possible UAF when remounting r/o a mmp-protected file system
ext4: use ext4_grp_locked_error in mb_find_extent
ext4: fix WARN_ON_ONCE(!buffer_uptodate) after an error writing the superblock
Revert "ext4: consolidate checks for resize of bigalloc into ext4_resize_begin"
The function jbd2_journal_unregister_shrinker() was getting called
twice when the file system was getting unmounted. On Power and ARM
platforms this was causing kernel crash when unmounting the file
system, when a percpu_counter was destroyed twice.
Fix this by removing jbd2_journal_[un]register_shrinker() functions,
and inlining the shrinker setup and teardown into
journal_init_common() and jbd2_journal_destroy(). This means that
ext4 and ocfs2 now no longer need to know about registering and
unregistering jbd2's shrinker.
Also, while we're at it, rename the percpu counter from
j_jh_shrink_count to j_checkpoint_jh_count, since this makes it
clearer what this counter is intended to track.
Link: https://lore.kernel.org/r/20210705145025.3363130-1-tytso@mit.edu
Fixes: 4ba3fcdde7 ("jbd2,ext4: add a shrinker to release checkpointed buffers")
Reported-by: Jon Hunter <jonathanh@nvidia.com>
Reported-by: Sachin Sant <sachinp@linux.vnet.ibm.com>
Tested-by: Sachin Sant <sachinp@linux.vnet.ibm.com>
Tested-by: Jon Hunter <jonathanh@nvidia.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
If a writeback of the superblock fails with an I/O error, the buffer
is marked not uptodate. However, this can cause a WARN_ON to trigger
when we attempt to write superblock a second time. (Which might
succeed this time, for cerrtain types of block devices such as iSCSI
devices over a flaky network.)
Try to detect this case in flush_stashed_error_work(), and also change
__ext4_handle_dirty_metadata() so we always set the uptodate flag, not
just in the nojournal case.
Before this commit, this problem can be repliciated via:
1. dmsetup create dust1 --table '0 2097152 dust /dev/sdc 0 4096'
2. mount /dev/mapper/dust1 /home/test
3. dmsetup message dust1 0 addbadblock 0 10
4. cd /home/test
5. echo "XXXXXXX" > t
After a few seconds, we got following warning:
[ 80.654487] end_buffer_async_write: bh=0xffff88842f18bdd0
[ 80.656134] Buffer I/O error on dev dm-0, logical block 0, lost async page write
[ 85.774450] EXT4-fs error (device dm-0): ext4_check_bdev_write_error:193: comm kworker/u16:8: Error while async write back metadata
[ 91.415513] mark_buffer_dirty: bh=0xffff88842f18bdd0
[ 91.417038] ------------[ cut here ]------------
[ 91.418450] WARNING: CPU: 1 PID: 1944 at fs/buffer.c:1092 mark_buffer_dirty.cold+0x1c/0x5e
[ 91.440322] Call Trace:
[ 91.440652] __jbd2_journal_temp_unlink_buffer+0x135/0x220
[ 91.441354] __jbd2_journal_unfile_buffer+0x24/0x90
[ 91.441981] __jbd2_journal_refile_buffer+0x134/0x1d0
[ 91.442628] jbd2_journal_commit_transaction+0x249a/0x3240
[ 91.443336] ? put_prev_entity+0x2a/0x200
[ 91.443856] ? kjournald2+0x12e/0x510
[ 91.444324] kjournald2+0x12e/0x510
[ 91.444773] ? woken_wake_function+0x30/0x30
[ 91.445326] kthread+0x150/0x1b0
[ 91.445739] ? commit_timeout+0x20/0x20
[ 91.446258] ? kthread_flush_worker+0xb0/0xb0
[ 91.446818] ret_from_fork+0x1f/0x30
[ 91.447293] ---[ end trace 66f0b6bf3d1abade ]---
Signed-off-by: Ye Bin <yebin10@huawei.com>
Link: https://lore.kernel.org/r/20210615090537.3423231-1-yebin10@huawei.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Pull ext4 updates from Ted Ts'o:
"In addition to bug fixes and cleanups, there are two new features for
ext4 in 5.14:
- Allow applications to poll on changes to
/sys/fs/ext4/*/errors_count
- Add the ioctl EXT4_IOC_CHECKPOINT which allows the journal to be
checkpointed, truncated and discarded or zero'ed"
* tag 'ext4_for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tytso/ext4: (32 commits)
jbd2: export jbd2_journal_[un]register_shrinker()
ext4: notify sysfs on errors_count value change
fs: remove bdev_try_to_free_page callback
ext4: remove bdev_try_to_free_page() callback
jbd2: simplify journal_clean_one_cp_list()
jbd2,ext4: add a shrinker to release checkpointed buffers
jbd2: remove redundant buffer io error checks
jbd2: don't abort the journal when freeing buffers
jbd2: ensure abort the journal if detect IO error when writing original buffer back
jbd2: remove the out label in __jbd2_journal_remove_checkpoint()
ext4: no need to verify new add extent block
jbd2: clean up misleading comments for jbd2_fc_release_bufs
ext4: add check to prevent attempting to resize an fs with sparse_super2
ext4: consolidate checks for resize of bigalloc into ext4_resize_begin
ext4: remove duplicate definition of ext4_xattr_ibody_inline_set()
ext4: fsmap: fix the block/inode bitmap comment
ext4: fix comment for s_hash_unsigned
ext4: use local variable ei instead of EXT4_I() macro
ext4: fix avefreec in find_group_orlov
ext4: correct the cache_nr in tracepoint ext4_es_shrink_exit
...
The function ext4_resize_begin() gets called from three different
places, and online resize for bigalloc file systems is disallowed from
the old-style online resize (EXT4_IOC_GROUP_ADD and
EXT4_IOC_GROUP_EXTEND), but it *is* supposed to be allowed via
EXT4_IOC_RESIZE_FS.
This reverts commit e9f9f61d0c.
After s_error_count is incremented, signal the change in the
corresponding sysfs attribute via sysfs_notify. This allows userspace to
poll() on changes to /sys/fs/ext4/*/errors_count.
[ Moved call of ext4_notify_error_sysfs() to flush_stashed_error_work()
to avoid BUG's caused by calling sysfs_notify trying to sleep after
being called from an invalid context. -- TYT ]
Signed-off-by: Jonathan Davies <jonathan.davies@nutanix.com>
Link: https://lore.kernel.org/r/20210611140209.28903-1-jonathan.davies@nutanix.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
After we introduce a jbd2 shrinker to release checkpointed buffer's
journal head, we could free buffer without bdev_try_to_free_page()
under memory pressure. So this patch remove the whole
bdev_try_to_free_page() callback directly. It also remove many
use-after-free issues relate to it together.
Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20210610112440.3438139-8-yi.zhang@huawei.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Current metadata buffer release logic in bdev_try_to_free_page() have
a lot of use-after-free issues when umount filesystem concurrently, and
it is difficult to fix directly because ext4 is the only user of
s_op->bdev_try_to_free_page callback and we may have to add more special
refcount or lock that is only used by ext4 into the common vfs layer,
which is unacceptable.
One better solution is remove the bdev_try_to_free_page callback, but
the real problem is we cannot easily release journal_head on the
checkpointed buffer, so try_to_free_buffers() cannot release buffers and
page under memory pressure, which is more likely to trigger
out-of-memory. So we cannot remove the callback directly before we find
another way to release journal_head.
This patch introduce a shrinker to free journal_head on the checkpointed
transaction. After the journal_head got freed, try_to_free_buffers()
could free buffer properly.
Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
Suggested-by: Jan Kara <jack@suse.cz>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20210610112440.3438139-6-yi.zhang@huawei.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
The in-kernel ext4 resize code doesn't support filesystem with the
sparse_super2 feature. It fails with errors like this and doesn't finish
the resize:
EXT4-fs (loop0): resizing filesystem from 16640 to 7864320 blocks
EXT4-fs warning (device loop0): verify_reserved_gdb:760: reserved GDT 2 missing grp 1 (32770)
EXT4-fs warning (device loop0): ext4_resize_fs:2111: error (-22) occurred during file system resize
EXT4-fs (loop0): resized filesystem to 2097152
To reproduce:
mkfs.ext4 -b 4096 -I 256 -J size=32 -E resize=$((256*1024*1024)) -O sparse_super2 ext4.img 65M
truncate -s 30G ext4.img
mount ext4.img /mnt
python3 -c 'import fcntl, os, struct ; fd = os.open("/mnt", os.O_RDONLY | os.O_DIRECTORY) ; fcntl.ioctl(fd, 0x40086610, struct.pack("Q", 30 * 1024 * 1024 * 1024 // 4096), False) ; os.close(fd)'
dmesg | tail
e2fsck ext4.img
The userspace resize2fs tool has a check for this case: it checks if the
filesystem has sparse_super2 set and if the kernel provides
/sys/fs/ext4/features/sparse_super2. However, the former check requires
manually reading and parsing the filesystem superblock.
Detect this case in ext4_resize_begin and error out early with a clear
error message.
Signed-off-by: Josh Triplett <josh@joshtriplett.org>
Link: https://lore.kernel.org/r/74b8ae78405270211943cd7393e65586c5faeed1.1623093259.git.josh@joshtriplett.org
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
ioctl EXT4_IOC_CHECKPOINT checkpoints and flushes the journal. This
includes forcing all the transactions to the log, checkpointing the
transactions, and flushing the log to disk. This ioctl takes u32 "flags"
as an argument. Three flags are supported. EXT4_IOC_CHECKPOINT_FLAG_DRY_RUN
can be used to verify input to the ioctl. It returns error if there is any
invalid input, otherwise it returns success without performing
any checkpointing. The other two flags, EXT4_IOC_CHECKPOINT_FLAG_DISCARD
and EXT4_IOC_CHECKPOINT_FLAG_ZEROOUT, can be used to issue requests to
discard or zeroout the journal logs blocks, respectively. At this
point, EXT4_IOC_CHECKPOINT_FLAG_ZEROOUT is primarily added to enable
testing of this codepath on devices that don't support discard.
EXT4_IOC_CHECKPOINT_FLAG_DISCARD and EXT4_IOC_CHECKPOINT_FLAG_ZEROOUT
cannot both be set.
Systems that wish to achieve content deletion SLO can set up a daemon
that calls this ioctl at a regular interval such that it matches with the
SLO requirement. Thus, with this patch, the ext4_dir_entry2 wipeout
patch[1], and the Ext4 "-o discard" mount option set, Ext4 can now
guarantee that all file contents, file metatdata, and filenames will not
be accessible through the filesystem and will have had discard or
zeroout requests issued for corresponding device blocks.
The __jbd2_journal_erase function could also be used to discard or
zero-fill the journal during journal load after recovery. This would
provide a potential solution to a journal replay bug reported earlier this
year[2]. After a successful journal recovery, e2fsck can call this ioctl to
discard the journal as well.
[1] https://lore.kernel.org/linux-ext4/YIHknqxngB1sUdie@mit.edu/
[2] https://lore.kernel.org/linux-ext4/YDZoaacIYStFQT8g@mit.edu/
Link: https://lore.kernel.org/r/20210518151327.130198-2-leah.rumancik@gmail.com
Signed-off-by: Leah Rumancik <leah.rumancik@gmail.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
