linux-toradex.git/fs/btrfs/raid56.c, branch v6.7

btrfs: scrub: avoid unnecessary csum tree search preparing stripes

2023-08-21T12:54:48+00:00

One of the bottleneck of the new scrub code is the extra csum tree
search.

The old code would only do the csum tree search for each scrub bio,
which can be as large as 512KiB, thus they can afford to allocate a new
path each time.

But the new scrub code is doing csum tree search for each stripe, which
is only 64KiB, this means we'd better re-use the same csum path during
each search.

This patch would introduce a per-sctx path for csum tree search, as we
don't need to re-allocate the path every time we need to do a csum tree
search.

With this change we can further improve the queue depth and improve the
scrub read performance:

Before (with regression and cached extent tree path):

 Device         r/s      rkB/s   rrqm/s  %rrqm r_await rareq-sz aqu-sz  %util
 nvme0n1p3 15875.00 1013328.00    12.00   0.08    0.08    63.83   1.35 100.00

After (with both cached extent/csum tree path):

 nvme0n1p3 17759.00 1133280.00    10.00   0.06    0.08    63.81   1.50 100.00

Fixes: e02ee89baa66 ("btrfs: scrub: switch scrub_simple_mirror() to scrub_stripe infrastructure")
CC: stable@vger.kernel.org # 6.4+
Signed-off-by: Qu Wenruo 
Reviewed-by: David Sterba 
Signed-off-by: David Sterba

btrfs: tracepoints: simplify raid56 events

2023-08-21T12:52:12+00:00

After commit 6bfd0133bee2 ("btrfs: raid56: switch scrub path to use a
single function"), the raid56 implementation no longer uses different
endio functions for RMW/recover/scrub.

All read operations end in submit_read_wait_bio_list(), while all write
operations end in submit_write_bios().  This means quite some trace
events are out-of-date and no longer utilized.

This patch would unify the trace events into just two:

- trace_raid56_read()
  Replaces trace_raid56_read_partial(), trace_raid56_scrub_read() and
  trace_raid56_scrub_read_recover().

- trace_raid56_write()
  Replaces trace_raid56_write_stripe() and
  trace_raid56_scrub_write_stripe().

Signed-off-by: Qu Wenruo 
Reviewed-by: David Sterba 
Signed-off-by: David Sterba

btrfs: raid56: remove unused BTRFS_RBIO_REBUILD_MISSING

2023-08-21T12:52:12+00:00

Commit aca43fe839e4 ("btrfs: remove unused raid56 functions which were
dedicated for scrub") removed the special handling of RAID56 scrub for
missing device.

As scrub goes full mirror_num based recovery, that means if it hits a
missing device in RAID56, it would just try the next mirror, which would
go through the BTRFS_RBIO_READ_REBUILD operation.

This means there is no longer any use of BTRFS_RBIO_REBUILD_MISSING
operation and we can safely remove it.

Reviewed-by: Christoph Hellwig 
Signed-off-by: Qu Wenruo 
Reviewed-by: David Sterba 
Signed-off-by: David Sterba

btrfs: raid56: always verify the P/Q contents for scrub

2023-07-18T01:13:15+00:00

[REGRESSION]
Commit 75b470332965 ("btrfs: raid56: migrate recovery and scrub recovery
path to use error_bitmap") changed the behavior of scrub_rbio().

Initially if we have no error reading the raid bio, we will assign
@need_check to true, then finish_parity_scrub() would later verify the
content of P/Q stripes before writeback.

But after that commit we never verify the content of P/Q stripes and
just writeback them.

This can lead to unrepaired P/Q stripes during scrub, or already
corrupted P/Q copied to the dev-replace target.

[FIX]
The situation is more complex than the regression, in fact the initial
behavior is not 100% correct either.

If we have the following rare case, it can still lead to the same
problem using the old behavior:

		0	16K	32K	48K	64K
	Data 1:	|IIIIIII|                       |
	Data 2:	|				|
	Parity:	|	|CCCCCCC|		|

Where "I" means IO error, "C" means corruption.

In the above case, we're scrubbing the parity stripe, then read out all
the contents of Data 1, Data 2, Parity stripes.

But found IO error in Data 1, which leads to rebuild using Data 2 and
Parity and got the correct data.

In that case, we would not verify if the Parity is correct for range
[16K, 32K).

So here we have to always verify the content of Parity no matter if we
did recovery or not.

This patch would remove the @need_check parameter of
finish_parity_scrub() completely, and would always do the P/Q
verification before writeback.

Fixes: 75b470332965 ("btrfs: raid56: migrate recovery and scrub recovery path to use error_bitmap")
CC: stable@vger.kernel.org # 6.2+
Signed-off-by: Qu Wenruo 
Signed-off-by: David Sterba

btrfs: scrub: use recovered data stripes as cache to avoid unnecessary read

2023-06-19T11:59:24+00:00

For P/Q stripe scrub, we have quite some duplicated read IO:

- Data stripes read for verification
  This is triggered by the scrub_submit_initial_read() inside
  scrub_raid56_parity_stripe().

- Data stripes read (again) for P/Q stripe verification
  This is triggered by scrub_assemble_read_bios() from scrub_rbio().

  Although we can have hit rbio cache and avoid unnecessary read, the
  chance is very low, as scrub would easily flush the whole rbio cache.

This means, even we're just scrubbing a single P/Q stripe, we would read
the data stripes twice for the best case scenario.  If we need to
recover some data stripes, it would cause more reads on the same data
stripes, again and again.

However before we call raid56_parity_submit_scrub_rbio() we already
have all data stripes repaired and their contents ready to use.
But RAID56 cache is unaware about the scrub cache, thus RAID56 layer
itself still needs to re-read the data stripes.

To avoid such cache miss, this patch would:

- Introduce a new helper, raid56_parity_cache_data_pages()
  This function would grab the pages from an array, and copy the content
  to the rbio, marking all the involved sectors uptodate.

  The page copy is unavoidable because of the cache pages of rbio are all
  self managed, thus can not utilize outside pages without screwing up
  the lifespan.

- Use the repaired data stripes as cache inside
  scrub_raid56_parity_stripe()

By this, we ensure all the data sectors of the scrub rbio are already
uptodate, and no need to read them again from disk.

Signed-off-by: Qu Wenruo 
Signed-off-by: David Sterba

btrfs: use SECTOR_SHIFT to convert LBA to physical offset

2023-06-19T11:59:23+00:00

Using SECTOR_SHIFT to convert LBA to physical address makes it more
readable.

Signed-off-by: Anand Jain 
Reviewed-by: David Sterba 
Signed-off-by: David Sterba

btrfs: use SECTOR_SHIFT to convert physical offset to LBA

2023-06-19T11:59:23+00:00

Use SECTOR_SHIFT while converting a physical address to an LBA, makes
it more readable.

Signed-off-by: Anand Jain 
Reviewed-by: David Sterba 
Signed-off-by: David Sterba

btrfs: remove unused raid56 functions which were dedicated for scrub

2023-04-17T17:52:18+00:00

Since the scrub rework, the following RAID56 functions are no longer
called:

- raid56_add_scrub_pages()
- raid56_alloc_missing_rbio()
- raid56_submit_missing_rbio()

Those functions are all utilized by scrub to handle missing device cases
for RAID56.

However the new scrub code handle them in a completely different way:

- If it's data stripe, go recovery path through btrfs_submit_bio()
- If it's P/Q stripe, it would be handled through
  raid56_parity_submit_scrub_rbio()
  And that function would handle dev-replace and repair properly.

Thus we can safely remove those functions.

Signed-off-by: Qu Wenruo 
Reviewed-by: David Sterba 
Signed-off-by: David Sterba

btrfs: scrub: introduce helper to find and fill sector info for a scrub_stripe

2023-04-17T16:01:23+00:00

The new helper will search the extent tree to find the first extent of a
logical range, then fill the sectors array by two loops:

- Loop 1 to fill common bits and metadata generation

- Loop 2 to fill csum data (only for data bgs)
  This loop will use the new btrfs_lookup_csums_bitmap() to fill
  the full csum buffer, and set scrub_sector_verification::csum.

With all the needed info filled by this function, later we only need to
submit and verify the stripe.

Here we temporarily export the helper to avoid warning on unused static
function.

Signed-off-by: Qu Wenruo 
Reviewed-by: David Sterba 
Signed-off-by: David Sterba

btrfs: use __bio_add_page to add single a page in rbio_add_io_sector

2023-04-17T16:01:20+00:00

The btrfs raid56 sector submission code uses bio_add_page() to add a
page to a newly created bio. bio_add_page() can fail, but the return
value is never checked.

Use __bio_add_page() as adding a single page to a newly created bio is
guaranteed to succeed.

This brings us a step closer to marking bio_add_page() as __must_check.

Reviewed-by: Damien Le Moal 
Signed-off-by: Johannes Thumshirn 
Reviewed-by: David Sterba 
Signed-off-by: David Sterba