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The members ::used and ::flags are now in the block group cache
structure, the last one is chunk_objectid, but that's set to a fixed
value and otherwise unused. The item is constructed from a local
variable before write, so we can remove the embedded one from block
group.
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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The flags are read from the item that's embedded to block group struct,
but the item will be removed. Use the ::flags after read and before
write.
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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For unknown reasons, the member 'used' in the block group struct is
stored in the b-tree item and accessed everywhere using the special
accessor helper. Let's unify it and make it a regular member and only
update the item before writing it to the tree.
The item is still being used for flags and chunk_objectid, there's some
duplication until the item is removed in following patches.
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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The last user of btrfs_bio::flags was removed in commit 326e1dbb5736
("block: remove management of bi_remaining when restoring original
bi_end_io"), remove it.
(Tagged for stable as the structure is heavily used and space savings
are desirable.)
CC: stable@vger.kernel.org # 4.4+
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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Add blake2b (with 256 bit digest) to the list of possible checksumming
algorithms used by BTRFS.
Signed-off-by: David Sterba <dsterba@suse.com>
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Currently all the checksum algorithms generate a fixed size digest size
and we use it. The on-disk format can hold up to BTRFS_CSUM_SIZE bytes
and BLAKE2b produces digest of 512 bits by default. We can't do that and
will use the blake2b-256, this needs to be passed to the crypto API.
Separate that from the base algorithm name and add a member to request
specific driver, in this case with the digest size.
The only place that uses the driver name is the crypto API setup.
Signed-off-by: David Sterba <dsterba@suse.com>
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Show the used driver for the checksum algorithm for the filesystem in
sysfs file /sys/fs/btrfs/UUID/features/checksum, eg.
crc32c (crc32c-generic)
Signed-off-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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Export supported checksum algorithms via sysfs in the list of static
features:
/sys/fs/btrfs/features/supported_checksums
Space spearated list of checksum algorithm names.
Co-developed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: David Sterba <dsterba@suse.com>
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Add sha256 to the list of possible checksumming algorithms used by BTRFS.
Signed-off-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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Add xxhash64 to the list of possible checksumming algorithms used by
BTRFS.
Signed-off-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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To remove use of extent_map::bdev we need to find a replacement, and the
latest_bdev is the only one we can use here, because inode::i_bdev and
superblock::s_bdev are NULL.
The DIO code uses bdev in two places:
* to read blocksize to perform alignment checks in
do_blockdev_direct_IO, but we do them in btrfs code before any call to
DIO
* in the following call chain:
do_direct_IO
get_more_blocks
sdio->get_block() <-- this is btrfs_get_blocks_direct
subsequently the map_bh->b_dev member is used in clean_bdev_aliases
and dio_new_bio to set the bio's bdev to that of the buffer_head.
However, because we have provided a submit function dio_bio_submit
calls our submission function and ignores the bdev.
So it's safe to pass any valid bdev that's used within the filesystem.
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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This is a preparatory patch for removing extent_map::bdev. There's some
history behind the code so this is only precaution to catch if things
break before the actual removal happens.
Logically, comparing a raw low-level block device (bdev) does not make
sense for extent maps (high-level objects). This had no effect in
practice but was quite confusing in the code. The lookup_map is set iff
EXTENT_FLAG_FS_MAPPING is set.
The two pointers were stored in the same bytes and used potentially in
two meanings. Now they're split, so the asserts are in place to check
that the condition will not change.
The lookup map pointer misused bdev, this has been changed in commit
95617d69326c ("btrfs: cleanup, stop casting for extent_map->lookup
everywhere") to the explicit type. But the semantics hasn't changed and
bdev was not actually used to decide if maps are mergeable.
Signed-off-by: David Sterba <dsterba@suse.com>
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Instead of checking if we've read a BTRFS_CHUNK_ITEM_KEY from disk and
then process it we could just bail out early if the read disk key wasn't
a BTRFS_CHUNK_ITEM_KEY.
This removes a level of indentation and makes the code nicer to read.
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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In btrfs_may_alloc_data_chunk() we're checking if the chunk type is of
type BTRFS_BLOCK_GROUP_DATA and if it is we process it.
Instead of checking if the chunk type is a BTRFS_BLOCK_GROUP_DATA chunk
we can negate the check and bail out early if it isn't.
This makes the code a bit more readable.
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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In lock_stripe_add() we're caching the bucket for the stripe hash table
just for a single call to dereference the stripe hash.
If we just directly call rbio_bucket() we can safe the pointless local
variable.
Also move the dereferencing of the stripe hash outside of the variable
declaration block to not break over the 80 characters limit.
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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In lock_stripe_add() we're traversing the stripe hash list and check if
the current list element's raid_map equals is equal to the raid bio's
raid_map. If both are equal we continue processing.
If we'd check for inequality instead of equality we can reduce one level
of indentation.
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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We don't modify the data passed to tracepoints, some of the declarations
are already const, add it to the rest.
Signed-off-by: David Sterba <dsterba@suse.com>
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Remove typecasts from trace printk, adjust types and move typecast to
the assignment if necessary. When assigning, the types are more obvious
compared to matching the variables to the format strings.
Signed-off-by: David Sterba <dsterba@suse.com>
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Instead of using an input pointer parameter as the return value and have
an int as the return type of find_desired_extent, rework the function to
directly return the found offset. Doing that the 'ret' variable in
btrfs_llseek_file can be removed. Additional (subjective) benefit is
that btrfs' llseek function now resemebles those of the other major
filesystems.
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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Handle SEEK_END/SEEK_CUR in a single 'default' case by directly
returning from generic_file_llseek. This makes the 'out' label
redundant. Finally return directly the vale from vfs_setpos. No
semantic changes.
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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Modifying the file position is done on a per-file basis. This renders
holding the inode lock for writing useless and makes the performance of
concurrent llseek's abysmal.
Fix this by holding the inode for read. This provides protection against
concurrent truncates and find_desired_extent already includes proper
extent locking for the range which ensures proper locking against
concurrent writes. SEEK_CUR and SEEK_END can be done lockessly.
The former is synchronized by file::f_lock spinlock. SEEK_END is not
synchronized but atomic, but that's OK since there is not guarantee that
SEEK_END will always be at the end of the file in the face of tail
modifications.
This change brings ~82% performance improvement when doing a lot of
parallel fseeks. The workload essentially does:
for (d=0; d<num_seek_read; d++)
{
/* offset %= 16777216; */
fseek (f, 256 * d % 16777216, SEEK_SET);
fread (buffer, 64, 1, f);
}
Without patch:
num workprocesses = 16
num fseek/fread = 8000000
step = 256
fork 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
real 0m41.412s
user 0m28.777s
sys 2m16.510s
With patch:
num workprocesses = 16
num fseek/fread = 8000000
step = 256
fork 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
real 0m11.479s
user 0m27.629s
sys 0m21.040s
Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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We can infer the ops from the type that is now passed to all functions
that would need it, this makes workspace_manager::ops redundant and can
be removed.
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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Replace indirect calls to free_workspace by switch and calls to the
specific callbacks. This is mainly to get rid of the indirection due to
spectre vulnerability mitigations.
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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We can infer the workspace_manager from type and the type will be used
in the following patch to call a common helper for free_workspace.
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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Replace indirect calls to alloc_workspace by switch and calls to the
specific callbacks. This is mainly to get rid of the indirection due to
spectre vulnerability mitigations.
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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We can infer the workspace_manager from type and the type will be used
in the following patch to call a common helper for alloc_workspace.
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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Similar to get_workspace, majority of the callbacks is trivial, we don't
gain anything by the indirection, so replace them by a switch function.
Trivial callback implementations use the helper.
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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Majority of the callbacks is trivial, we don't gain anything by the
indirection, so replace them by a switch function.
ZLIB needs to adjust level in the callback and ZSTD workspace management
is complex, the rest is call to the helper.
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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The indirect calls will be replaced by a switch in compression.c.
(Switch is faster than indirect calls with when Spectre mitigations are
enabled).
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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Replace loop calling to all algos with a list of direct calls to the
cleanup manager callback. When that becomes trivial it is replaced by
direct call to the helper.
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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With the access to the workspace structures, we can look it up together
with the compression ops inside the workspace manager cleanup helper.
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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Replace loop calling to all algos with a list of direct calls to the
init manager callback. When that becomes trivial it is replaced by
direct call to the helper.
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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With the access to the workspace structures, we can look it up together
with the compression ops inside the workspace manager init helper.
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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There's a lot of indirection when the generic code calls into
algo-specific callbacks to reach the private workspace manager structure
and back to the generic code.
To simplify that, export the workspace manager for heuristic, LZO and
ZLIB, while ZSTD is going to use it's own manager.
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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The indirect calls bring some overhead due to spectre vulnerability
mitigations. The number of cases is small and below the threshold
(10-20) where indirect call would be better.
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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Export compress_pages, decompress_bio and decompress callbacks for all
compression algos. The indirect calls will be replaced by a switch.
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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When free'ing extents in a block group we check to see if the block
group is not cached, and then cache it if we need to. However we'll
just carry on as long as we're loading the cache. This is problematic
because we are dirtying the block group here. If we are fast enough we
could do a transaction commit and clear the free space cache while we're
still loading the space cache in another thread. This truncates the
free space inode, which will keep it from loading the space cache.
Fix this by using the btrfs_block_group_cache_done helper so that we try
to load the space cache unconditionally here, which will result in the
caller waiting for the fast caching to complete and keep us from
truncating the free space inode.
CC: stable@vger.kernel.org # 4.4+
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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While testing 5.2 we ran into the following panic
[52238.017028] BUG: kernel NULL pointer dereference, address: 0000000000000001
[52238.105608] RIP: 0010:drop_buffers+0x3d/0x150
[52238.304051] Call Trace:
[52238.308958] try_to_free_buffers+0x15b/0x1b0
[52238.317503] shrink_page_list+0x1164/0x1780
[52238.325877] shrink_inactive_list+0x18f/0x3b0
[52238.334596] shrink_node_memcg+0x23e/0x7d0
[52238.342790] ? do_shrink_slab+0x4f/0x290
[52238.350648] shrink_node+0xce/0x4a0
[52238.357628] balance_pgdat+0x2c7/0x510
[52238.365135] kswapd+0x216/0x3e0
[52238.371425] ? wait_woken+0x80/0x80
[52238.378412] ? balance_pgdat+0x510/0x510
[52238.386265] kthread+0x111/0x130
[52238.392727] ? kthread_create_on_node+0x60/0x60
[52238.401782] ret_from_fork+0x1f/0x30
The page we were trying to drop had a page->private, but had no
page->mapping and so called drop_buffers, assuming that we had a
buffer_head on the page, and then panic'ed trying to deref 1, which is
our page->private for data pages.
This is happening because we're truncating the free space cache while
we're trying to load the free space cache. This isn't supposed to
happen, and I'll fix that in a followup patch. However we still
shouldn't allow those sort of mistakes to result in messing with pages
that do not belong to us. So add the page->mapping check to verify that
we still own this page after dropping and re-acquiring the page lock.
This page being unlocked as:
btrfs_readpage
extent_read_full_page
__extent_read_full_page
__do_readpage
if (!nr)
unlock_page <-- nr can be 0 only if submit_extent_page
returns an error
CC: stable@vger.kernel.org # 4.4+
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
[ add callchain ]
Signed-off-by: David Sterba <dsterba@suse.com>
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In the fixup worker, if we fail to mark the range as delalloc in the io
tree, we must release the previously reserved metadata, as well as update
the outstanding extents counter for the inode, otherwise we leak metadata
space.
In pratice we can't return an error from btrfs_set_extent_delalloc(),
which is just a wrapper around __set_extent_bit(), as for most errors
__set_extent_bit() does a BUG_ON() (or panics which hits a BUG_ON() as
well) and returning an -EEXIST error doesn't happen in this case since
the exclusive bits parameter always has a value of 0 through this code
path. Nevertheless, just fix the error handling in the fixup worker,
in case one day __set_extent_bit() can return an error to this code
path.
Fixes: f3038ee3a3f101 ("btrfs: Handle btrfs_set_extent_delalloc failure in fixup worker")
CC: stable@vger.kernel.org # 4.19+
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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When doing a buffered write it's possible to leave the subv_writers
counter of the root, used for synchronization between buffered nocow
writers and snapshotting. This happens in an exceptional case like the
following:
1) We fail to allocate data space for the write, since there's not
enough available data space nor enough unallocated space for allocating
a new data block group;
2) Because of that failure, we try to go to NOCOW mode, which succeeds
and therefore we set the local variable 'only_release_metadata' to true
and set the root's sub_writers counter to 1 through the call to
btrfs_start_write_no_snapshotting() made by check_can_nocow();
3) The call to btrfs_copy_from_user() returns zero, which is very unlikely
to happen but not impossible;
4) No pages are copied because btrfs_copy_from_user() returned zero;
5) We call btrfs_end_write_no_snapshotting() which decrements the root's
subv_writers counter to 0;
6) We don't set 'only_release_metadata' back to 'false' because we do
it only if 'copied', the value returned by btrfs_copy_from_user(), is
greater than zero;
7) On the next iteration of the while loop, which processes the same
page range, we are now able to allocate data space for the write (we
got enough data space released in the meanwhile);
8) After this if we fail at btrfs_delalloc_reserve_metadata(), because
now there isn't enough free metadata space, or in some other place
further below (prepare_pages(), lock_and_cleanup_extent_if_need(),
btrfs_dirty_pages()), we break out of the while loop with
'only_release_metadata' having a value of 'true';
9) Because 'only_release_metadata' is 'true' we end up decrementing the
root's subv_writers counter to -1 (through a call to
btrfs_end_write_no_snapshotting()), and we also end up not releasing the
data space previously reserved through btrfs_check_data_free_space().
As a consequence the mechanism for synchronizing NOCOW buffered writes
with snapshotting gets broken.
Fix this by always setting 'only_release_metadata' to false at the start
of each iteration.
Fixes: 8257b2dc3c1a ("Btrfs: introduce btrfs_{start, end}_nocow_write() for each subvolume")
Fixes: 7ee9e4405f26 ("Btrfs: check if we can nocow if we don't have data space")
CC: stable@vger.kernel.org # 4.4+
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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Some functions are doing some unnecessary indirection to reach the
btrfs_fs_info struct. Change these functions to receive a btrfs_fs_info
struct instead of a *file.
Reviewed-by: Anand Jain <anand.jain@oracle.com>
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Marcos Paulo de Souza <mpdesouza@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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We don't need int argument bool shall do in free_root_pointers(). And
rename the argument as it confused two people.
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Anand Jain <anand.jain@oracle.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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The compression type upper limit constant is the same as the last value
and this is confusing. In order to keep coding style consistent, use
BTRFS_NR_COMPRESS_TYPES as the total number that follows the idom of
'NR' being one more than the last value.
Signed-off-by: Chengguang Xu <cgxu519@mykernel.net>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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Use enum to replace macro definitions of extent types.
Signed-off-by: Chengguang Xu <cgxu519@mykernel.net>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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DEFINE_HASHTABLE itself has already included initialization code,
we don't have to call hash_init() again, so remove it.
Signed-off-by: Chengguang Xu <cgxu519@mykernel.net>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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This function is used only during the final phase of freespace cache
writeout. This is necessary since using the plain btrfs_join_transaction
api is deadlock prone. The deadlock looks like:
T1:
btrfs_commit_transaction
commit_cowonly_roots
btrfs_write_dirty_block_groups
btrfs_wait_cache_io
__btrfs_wait_cache_io
btrfs_wait_ordered_range <-- Triggers ordered IO for freespace
inode and blocks transaction commit
until freespace cache writeout
T2: <-- after T1 has triggered the writeout
finish_ordered_fn
btrfs_finish_ordered_io
btrfs_join_transaction <--- this would block waiting for current
transaction to commit, but since trans
commit is waiting for this writeout to
finish
The special purpose functions prevents it by simply skipping the "wait
for writeout" since it's guaranteed the transaction won't proceed until
we are done.
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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Using an ASSERT in btrfs_pin_extent allows to more stringently observe
whether the function is called under a transaction or not.
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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The helper is trivial and we can understand what the atomic_inc on
something named refs does.
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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During a cyclic writeback, extent_write_cache_pages() uses done_index
to update the writeback_index after the current run is over. However,
instead of current index + 1, it gets to to the current index itself.
Unfortunately, this, combined with returning on EOF instead of looping
back, can lead to the following pathlogical behavior.
1. There is a single file which has accumulated enough dirty pages to
trigger balance_dirty_pages() and the writer appending to the file
with a series of short writes.
2. balance_dirty_pages kicks in, wakes up background writeback and sleeps.
3. Writeback kicks in and the cursor is on the last page of the dirty
file. Writeback is started or skipped if already in progress. As
it's EOF, extent_write_cache_pages() returns and the cursor is set
to done_index which is pointing to the last page.
4. Writeback is done. Nothing happens till balance_dirty_pages
finishes, at which point we go back to #1.
This can almost completely stall out writing back of the file and keep
the system over dirty threshold for a long time which can mess up the
whole system. We encountered this issue in production with a package
handling application which can reliably reproduce the issue when
running under tight memory limits.
Reading the comment in the error handling section, this seems to be to
avoid accidentally skipping a page in case the write attempt on the
page doesn't succeed. However, this concern seems bogus.
On each page, the code either:
* Skips and moves onto the next page.
* Fails issue and sets done_index to index + 1.
* Successfully issues and continue to the next page if budget allows
and not EOF.
IOW, as long as it's not EOF and there's budget, the code never
retries writing back the same page. Only when a page happens to be
the last page of a particular run, we end up retrying the page, which
can't possibly guarantee anything data integrity related. Besides,
cyclic writes are only used for non-syncing writebacks meaning that
there's no data integrity implication to begin with.
Fix it by always setting done_index past the current page being
processed.
Note that this problem exists in other writepages too.
CC: stable@vger.kernel.org # 4.19+
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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Commit 4617ea3a52cf (" Btrfs: fix necessary chunk tree space calculation
when allocating a chunk") removed the is_allocation argument from
check_system_chunk, since the formula for reserving the necessary space
for allocation or removing a chunk would be the same.
So, rework the comment by removing the mention of is_allocation
argument.
Signed-off-by: Marcos Paulo de Souza <marcos.souza.org@gmail.com>
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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David Sterba
Qu Wenruo
Johannes Thumshirn
Nikolay Borisov
Josef Bacik
Filipe Manana
Marcos Paulo de Souza
Anand Jain
Chengguang Xu
Tejun Heo