There are several bug reports of ENOSPC error in
btrfs_run_delalloc_range().
With some extra info from one reporter, it turns out that
can_overcommit() is using a wrong way to calculate allocatable metadata
space.
The most typical case would look like:
devid 1 unallocated: 1G
devid 2 unallocated: 10G
metadata profile: RAID1
In above case, we can at most allocate 1G chunk for metadata, due to
unbalanced disk free space.
But current can_overcommit() uses factor based calculation, which never
consider the disk free space balance.
To address this problem, here comes the per-profile available space
array, which gets updated every time a chunk get allocated/removed or a
device get grown or shrunk.
This provides a quick way for hotter place like can_overcommit() to grab
an estimation on how many bytes it can over-commit.
The per-profile available space calculation tries to keep the behavior
of chunk allocator, thus it can handle uneven disks pretty well.
And statfs() can also grab that pre-calculated value for instance usage.
Since this patch introduced a new failure pattern, some new error
handling are introduced:
- __btrfs_alloc_chunk()
At the end of that function where calc_per_profile_avail() get called,
if it failed due to -ENOMEM, we will revert device used space, and
remove the allocated chunk.
This is the only new error handling added by patch 5.
- btrfs_remove_chunk()
There is no good way to revert the change. So here we abort
transaction, just like what the old error handling does.
- btrfs_grow_device()
This function has its problem by not reverting device used space from
the very beginning.
This patchset will enhance it in patch 4.
- btrfs_shrink_device()
- btrfs_init_new_device()
- btrfs_rm_device()
This function already has good error handling, reuse it.
- btrfs_verify_dev_extents()
Mount time error will lead to mount failure, nothing to worry about.
Contents of the patchset:
Patch 1: Core facility, with basic (not perfect) error handling
Patch 2: Fix for over-confident can_overcommit()
Patch 3: Make statfs() more accurate
Patch 4: Better error handling for btrfs_grow_device()
Patch 5: Better error handling for __btrfs_alloc_chunk()
If needed, patch 4 and patch 5 can be merged into patch 1.
Changelog:
v1:
- Fix a bug where we forgot to update per-profile array after allocating
a chunk.
To avoid ABBA deadlock, this introduce a small windows at the end
__btrfs_alloc_chunk(), it's not elegant but should be good enough
before we rework chunk and device list mutex.
- Make statfs() to use virtual chunk allocator to do better estimation
Now statfs() can report not only more accurate result, but can also
handle RAID5/6 better.
v2:
- Fix a deadlock caused by acquiring device_list_mutex under
__btrfs_alloc_chunk()
There is no need to acquire device_list_mutex when holding
chunk_mutex.
Fix it and remove the lockdep assert.
v3:
- Use proper chunk_mutex instead of device_list_mutex
Since they are protecting two different things, and we only care about
alloc_list, we should only use chunk_mutex.
With improved lock situation, it's easier to fold
calc_per_profile_available() calls into the first patch.
- Add performance benchmark for statfs() modification
As Facebook seems to run into some problems with statfs() calls, add
some basic ftrace results.
v4:
- Keep the lock-free design for statfs()
As extra sleeping in statfs() may not be a good idea, keep the old
lock-free design, and use factor based calculation as fall back.
v5:
- Enhance btrfs_update_device() error handling in btrfs_grow_device()
- Ensure all failure caused by calc_per_profile_available() is the same
with existing error handling
- Fix a bug where chunk_mutex is not released in btrfs_shrink_device()
v6:
- Don't update the array if we hit any error.
To avoid calling calc_per_profile_avail() in error handling path.
- Re-order the patchset
Make the core facility the first patch.
Error handling improvement in later patches.
- Add better error handling
Improve one existing bad error handling, and provide a better solution
for __btrfs_alloc_chunk()
v7:
- Remove btrfs_calc_avail_data_space() completely
Now we only need to grab the pre-calculated number, no need for a
function over 100 lines.
- Keep the 0-avail-if-metadata-exhausted behavior
Now it's handled by space_info->full, which indicates if we can
allocate new chunks in metadata space info.
We have no need to bother that now.
v8:
- Cosmetic changes
* Comment fixes
* Use rounddown() to replace one open-code
* while() loop reformat
* Remove one redundant 0-size check
* Add one lockdep_assert() for calc_one_profile_avail()
* Use atomic64_t to remove spinlock
- Add two more timing to call calc_per_profile_avail()
* btrfs_rm_device()
* btrfs_init_new_device()
v9:
- Rebased to latest misc-next branch
Minor conflicts due to chunk allocator refactor
- Remove redundant virtual allocation clear
Qu Wenruo (5):
btrfs: Introduce per-profile available space facility
btrfs: space-info: Use per-profile available space in can_overcommit()
btrfs: statfs: Use pre-calculated per-profile available space
btrfs: Reset device size when btrfs_update_device() failed in
btrfs_grow_device()
btrfs: volumes: Revert device used bytes when calc_per_profile_avail()
failed
fs/btrfs/space-info.c | 14 +--
fs/btrfs/super.c | 131 ++---------------------
fs/btrfs/volumes.c | 242 ++++++++++++++++++++++++++++++++++++++----
fs/btrfs/volumes.h | 10 ++
4 files changed, 244 insertions(+), 153 deletions(-)
--
2.26.2
