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There are two cases open coding the clear and wake up pattern, we can
use the helper.
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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So far we've been deriving the buffer tree index using the sector size.
But each extent buffer covers multiple sectors. This makes the buffer
tree rather sparse.
For example the typical and quite common configuration uses sector size
of 4KiB and node size of 16KiB. In this case it means the buffer tree is
using up to the maximum of 25% of it's slots. Or in other words at least
75% of the tree slots are wasted as never used.
We can score significant memory savings on the required tree nodes by
indexing the tree using the node size instead. As a result far less
slots are wasted and the tree can now use up to all 100% of it's slots
this way.
Note: This works even with unaligned tree blocks as we can still get
unique index by doing eb->start >> nodesize_shift.
Getting some stats from running fio write test, there is a bit of
variance. The values presented in the table below are medians from 5
test runs. The numbers are:
- # of allocated ebs in the tree
- # of leaf tree nodes
- highest index in the tree (radix tree width)):
ebs / leaves / Index | bare for-next | with fix
---------------------+--------------------+-------------------
post mount | 16 / 11 / 10e5c | 16 / 10 / 4240
post test | 5810 / 891 / 11cfc | 4420 / 252 / 473a
post rm | 574 / 300 / 10ef0 | 540 / 163 / 46e9
In this case (10GiB filesystem) the height of the tree is still 3 levels
but the 4x width reduction is clearly visible as expected. But since the
tree is more dense we can see the 54-72% reduction of leaf nodes. That's
very close to ideal with this test. It means the tree is getting really
dense with this kind of workload.
Also, the fio results show no performance change.
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Daniel Vacek <neelx@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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We recently received a report of poor performance doing sequential
buffered reads of a file with compressed extents. With bs=128k, a naive
sequential dd ran as fast on a compressed file as on an uncompressed
(1.2GB/s on my reproducing system) while with bs<32k, this performance
tanked down to ~300MB/s.
i.e., slow:
dd if=some-compressed-file of=/dev/null bs=4k count=X
vs fast:
dd if=some-compressed-file of=/dev/null bs=128k count=Y
The cause of this slowness is overhead to do with looking up extent_maps
to enable readahead pre-caching on compressed extents
(add_ra_bio_pages()), as well as some overhead in the generic VFS
readahead code we hit more in the slow case. Notably, the main
difference between the two read sizes is that in the large sized request
case, we call btrfs_readahead() relatively rarely while in the smaller
request we call it for every compressed extent. So the fast case stays
in the btrfs readahead loop:
while ((folio = readahead_folio(rac)) != NULL)
btrfs_do_readpage(folio, &em_cached, &bio_ctrl, &prev_em_start);
where the slower one breaks out of that loop every time. This results in
calling add_ra_bio_pages a lot, doing lots of extent_map lookups,
extent_map locking, etc.
This happens because although add_ra_bio_pages() does add the
appropriate un-compressed file pages to the cache, it does not
communicate back to the ractl in any way. To solve this, we should be
using readahead_expand() to signal to readahead to expand the readahead
window.
This change passes the readahead_control into the btrfs_bio_ctrl and in
the case of compressed reads sets the expansion to the size of the
extent_map we already looked up anyway. It skips the subpage case as
that one already doesn't do add_ra_bio_pages().
With this change, whether we use bs=4k or bs=128k, btrfs expands the
readahead window up to the largest compressed extent we have seen so far
(in the trivial example: 128k) and the call stacks of the two modes look
identical. Notably, we barely call add_ra_bio_pages at all. And the
performance becomes identical as well. So this change certainly "fixes"
this performance problem.
Of course, it does seem to beg a few questions:
1. Will this waste too much page cache with a too large ra window?
2. Will this somehow cause bugs prevented by the more thoughtful
checking in add_ra_bio_pages?
3. Should we delete add_ra_bio_pages?
My stabs at some answers:
1. Hard to say. See attempts at generic performance testing below. Is
there a "readahead_shrink" we should be using? Should we expand more
slowly, by half the remaining em size each time?
2. I don't think so. Since the new behavior is indistinguishable from
reading the file with a larger read size passed in, I don't see why
one would be safe but not the other.
3. Probably! I tested that and it was fine in fstests, and it seems like
the pages would get re-used just as well in the readahead case.
However, it is possible some reads that use page cache but not
btrfs_readahead() could suffer. I will investigate this further as a
follow up.
I tested the performance implications of this change in 3 ways (using
compress-force=zstd:3 for compression):
Directly test the affected workload of small sequential reads on a
compressed file (improved from ~250MB/s to ~1.2GB/s)
==========for-next==========
dd /mnt/lol/non-cmpr 4k
1048576+0 records in
1048576+0 records out
4294967296 bytes (4.3 GB, 4.0 GiB) copied, 6.02983 s, 712 MB/s
dd /mnt/lol/non-cmpr 128k
32768+0 records in
32768+0 records out
4294967296 bytes (4.3 GB, 4.0 GiB) copied, 5.92403 s, 725 MB/s
dd /mnt/lol/cmpr 4k
1048576+0 records in
1048576+0 records out
4294967296 bytes (4.3 GB, 4.0 GiB) copied, 17.8832 s, 240 MB/s
dd /mnt/lol/cmpr 128k
32768+0 records in
32768+0 records out
4294967296 bytes (4.3 GB, 4.0 GiB) copied, 3.71001 s, 1.2 GB/s
==========ra-expand==========
dd /mnt/lol/non-cmpr 4k
1048576+0 records in
1048576+0 records out
4294967296 bytes (4.3 GB, 4.0 GiB) copied, 6.09001 s, 705 MB/s
dd /mnt/lol/non-cmpr 128k
32768+0 records in
32768+0 records out
4294967296 bytes (4.3 GB, 4.0 GiB) copied, 6.07664 s, 707 MB/s
dd /mnt/lol/cmpr 4k
1048576+0 records in
1048576+0 records out
4294967296 bytes (4.3 GB, 4.0 GiB) copied, 3.79531 s, 1.1 GB/s
dd /mnt/lol/cmpr 128k
32768+0 records in
32768+0 records out
4294967296 bytes (4.3 GB, 4.0 GiB) copied, 3.69533 s, 1.2 GB/s
Built the linux kernel from clean (no change)
Ran fsperf. Mostly neutral results with some improvements and
regressions here and there.
Reported-by: Dimitrios Apostolou <jimis@gmx.net>
Link: https://lore.kernel.org/linux-btrfs/34601559-6c16-6ccc-1793-20a97ca0dbba@gmx.net/
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Boris Burkov <boris@bur.io>
Signed-off-by: David Sterba <dsterba@suse.com>
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Any conversion of offsets in the logical or the physical mapping space
of the pages is done by a shift and the target type should be pgoff_t
(type of struct page::index). Fix the locations where it's still
unsigned long.
Signed-off-by: David Sterba <dsterba@suse.com>
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Our message helpers accept NULL for the fs_info in the context that does
not provide and print the common header of the message. The use of pr_*
helpers is only for special reasons, like module loading, device
scanning or multi-line output (print-tree).
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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All the callers want is to determine if a bit is set and all of them call
the function and do a double negation (!!) on its result to get a boolean.
So change it to return a boolean and simplify callers.
Reviewed-by: Boris Burkov <boris@bur.io>
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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Simplify folio_pos() + folio_size() and use the new helper.
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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A few more remaining cases where we can use the helper.
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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Instead of using a bare atomic, use the refcount_t type, which despite
being a structure that contains only an atomic, has an API that checks
for underflows and other hazards. This doesn't change the size of the
extent_buffer structure.
This removes the need to do things like this:
WARN_ON(atomic_read(&eb->refs) == 0);
if (atomic_dec_and_test(&eb->refs)) {
(...)
}
And do just:
if (refcount_dec_and_test(&eb->refs)) {
(...)
}
Since refcount_dec_and_test() already triggers a warning when we decrement
a ref count that has a value of 0 (or below zero).
Reviewed-by: Boris Burkov <boris@bur.io>
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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There's this special atomic compare and exchange logic which serves to
avoid locking the extent buffers refs_lock spinlock and therefore reduce
lock contention, so add a comment to make it more obvious.
Reviewed-by: Boris Burkov <boris@bur.io>
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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It's hard to read the logic to break out of the while loop since it's a
very long expression consisting of a logical or of two composite
expressions, each one composed by a logical and. Further each one is also
testing for the EXTENT_BUFFER_UNMAPPED bit, making it more verbose than
necessary.
So change from this:
if ((!test_bit(EXTENT_BUFFER_UNMAPPED, &eb->bflags) && refs <= 3)
|| (test_bit(EXTENT_BUFFER_UNMAPPED, &eb->bflags) &&
refs == 1))
break;
To this:
if (test_bit(EXTENT_BUFFER_UNMAPPED, &eb->bflags)) {
if (refs == 1)
break;
} else if (refs <= 3) {
break;
}
At least on x86_64 using gcc 9.3.0, this doesn't change the object size.
Reviewed-by: Boris Burkov <boris@bur.io>
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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With the incoming large data folios support, the structure name
btrfs_subpage is no longer correct, as for we can have multiple blocks
inside a large folio, and the block size is still page size.
So to follow the schema of iomap, rename btrfs_subpage to
btrfs_folio_state, along with involved enums.
There are still exported functions with "btrfs_subpage_" prefix, and I
believe for metadata the name "subpage" will stay forever as we will
never allocate a folio larger than nodesize anyway.
The full cleanup of the word "subpage" will happen in much smaller steps
in the future.
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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If we break out of the loop because an extent buffer doesn't have the bit
EXTENT_BUFFER_TREE_REF set, we end up unlocking the xarray twice, once
before we tested for the bit and break out of the loop, and once again
after the loop.
Fix this by testing the bit and exiting before unlocking the xarray.
The time spent testing the bit is negligible and it's not worth trying
to do that outside the critical section delimited by the xarray lock due
to the code complexity required to avoid it (like using a local boolean
variable to track whether the xarray is locked or not). The xarray unlock
only needs to be done before calling release_extent_buffer(), as that
needs to lock the xarray (through xa_cmpxchg_irq()) and does a more
significant amount of work.
Fixes: 19d7f65f032f ("btrfs: convert the buffer_radix to an xarray")
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Link: https://lore.kernel.org/linux-btrfs/aDRNDU0GM1_D4Xnw@stanley.mountain/
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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In the zoned mode there's a bug in the extent buffer tree conversion to
xarray. The reference for eb is dropped and code continues but the
references get dropped by releasing the batch.
Reported-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Fixes: 19d7f65f032f ("btrfs: convert the buffer_radix to an xarray")
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Tested-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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The (correct) commit e41c81d0d30e ("mm/truncate: Replace page_mapped()
call in invalidate_inode_page()") replaced the page_mapped(page) check
with a refcount check. However, this refcount check does not work as
expected with drop_caches for btrfs's metadata pages.
Btrfs has a per-sb metadata inode with cached pages, and when not in
active use by btrfs, they have a refcount of 3. One from the initial
call to alloc_pages(), one (nr_pages == 1) from filemap_add_folio(), and
one from folio_attach_private(). We would expect such pages to get dropped
by drop_caches. However, drop_caches calls into mapping_evict_folio() via
mapping_try_invalidate() which gets a reference on the folio with
find_lock_entries(). As a result, these pages have a refcount of 4, and
fail this check.
For what it's worth, such pages do get reclaimed under memory pressure,
so I would say that while this behavior is surprising, it is not really
dangerously broken.
When I asked the mm folks about the expected refcount in this case, I
was told that the correct thing to do is to donate the refcount from the
original allocation to the page cache after inserting it.
Therefore, attempt to fix this by adding a put_folio() to the critical
spot in alloc_extent_buffer() where we are sure that we have really
allocated and attached new pages. We must also adjust
folio_detach_private() to properly handle being the last reference to the
folio and not do a use-after-free after folio_detach_private().
extent_buffers allocated by clone_extent_buffer() and
alloc_dummy_extent_buffer() are unmapped, so this transfer of ownership
from allocation to insertion in the mapping does not apply to them.
However, we can still folio_put() them safely once they are finished
being allocated and have called folio_attach_private().
Finally, removing the generic put_folio() for the allocation from
btrfs_detach_extent_buffer_folios() means we need to be careful to do
the appropriate put_folio() in allocation failure paths in
alloc_extent_buffer(), clone_extent_buffer() and
alloc_dummy_extent_buffer().
Link: https://lore.kernel.org/linux-mm/ZrwhTXKzgDnCK76Z@casper.infradead.org/
Tested-by: Klara Modin <klarasmodin@gmail.com>
Reviewed-by: Daniel Vacek <neelx@suse.com>
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Boris Burkov <boris@bur.io>
Signed-off-by: David Sterba <dsterba@suse.com>
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The `free_eb` label is used only once. Simplify by moving the code inplace.
Signed-off-by: Daniel Vacek <neelx@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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Currently we have this ugly back and forth with the btree writeback
where we find the folio, find the eb associated with that folio, and
then attempt to writeback. This results in two different paths for
subpage ebs and >= page size ebs.
Clean this up by adding our own infrastructure around looking up tagged
ebs and writing the ebs out directly. This allows us to unify the
subpage and >= pagesize IO paths, resulting in a much cleaner writeback
path for extent buffers.
I ran this through fsperf on a VM with 8 CPUs and 16GiB of RAM. I used
smallfiles100k, but reduced the files to 1k to make it run faster, the
results are as follows, with the statistically significant improvements
marked with *, there were no regressions. fsperf was run with -n 10 for
both runs, so the baseline is the average 10 runs and the test is the
average of 10 runs.
smallfiles100k results
metric baseline current stdev diff
================================================================================
avg_commit_ms 68.58 58.44 3.35 -14.79% *
commits 270.60 254.70 16.24 -5.88%
dev_read_iops 48 48 0 0.00%
dev_read_kbytes 1044 1044 0 0.00%
dev_write_iops 866117.90 850028.10 14292.20 -1.86%
dev_write_kbytes 10939976.40 10605701.20 351330.32 -3.06%
elapsed 49.30 33 1.64 -33.06% *
end_state_mount_ns 41251498.80 35773220.70 2531205.32 -13.28% *
end_state_umount_ns 1.90e+09 1.50e+09 14186226.85 -21.38% *
max_commit_ms 139 111.60 9.72 -19.71% *
sys_cpu 4.90 3.86 0.88 -21.29%
write_bw_bytes 42935768.20 64318451.10 1609415.05 49.80% *
write_clat_ns_mean 366431.69 243202.60 14161.98 -33.63% *
write_clat_ns_p50 49203.20 20992 264.40 -57.34% *
write_clat_ns_p99 827392 653721.60 65904.74 -20.99% *
write_io_kbytes 2035940 2035940 0 0.00%
write_iops 10482.37 15702.75 392.92 49.80% *
write_lat_ns_max 1.01e+08 90516129 3910102.06 -10.29% *
write_lat_ns_mean 366556.19 243308.48 14154.51 -33.62% *
As you can see we get about a 33% decrease runtime, with a 50%
throughput increase, which is pretty significant.
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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In preparation for changing how we do writeout of extent buffers, start
tagging the extent buffer xarray with DIRTY and WRITEBACK to make it
easier to find extent buffers that are in either state.
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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In order to fully utilize xarray tagging to improve writeback we need to
convert the buffer_radix to a proper xarray. This conversion is
relatively straightforward as the radix code uses the xarray underneath.
Using xarray directly allows for quite a lot less code.
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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When btrfs subpage support (fs block < page size) was introduced, a
subpage filesystem will only reject tree blocks which cross page
boundaries.
This used to be a compromise to simplify the tree block handling and
still allowing subpage cases to read some old converted filesystems
which did not have proper chunk alignment.
But in practice, suppose we have the following unaligned tree block on a
64K page sized system:
0 32K 44K 60K 64K
| |///////////////| |
Although btrfs has no problem reading the tree block at [44K, 60K), if
extent allocator is allocating another tree block, it may choose the
range [60K, 74K), as extent allocator has no awareness if it's a subpage
metadata request or not.
Then we'd get -EINVAL from the following sequence:
btrfs_alloc_tree_block()
|- btrfs_reserve_extent()
| Which returned range [60K, 74K)
|- btrfs_init_new_buffer()
|- btrfs_find_create_tree_block()
|- alloc_extent_buffer()
|- check_eb_alignment()
Which returned -EINVAL, because the range crosses page
boundary.
This situation will not fix itself and should mostly mark the fs
read-only.
Thankfully we didn't really get such reports in the real world because:
- The original unaligned tree block is only caused by older
btrfs-convert
It's before the btrfs-convert rework was done in v4.6, where converted
btrfs filesystem can have metadata block groups which are not aligned
to nodesize nor stripe size (64K).
But after btrfs-progs v4.6, all chunks allocated will be stripe (64K)
aligned, thus no more such problem.
Considering how old the fix is (v4.6 was released almost 10 years ago),
subpage support for btrfs was introduced in v5.15, it should be safe to
reject those unaligned tree blocks.
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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This is just a trivial change. The code looks a bit more readable this way, IMO.
Move initialization of existing_folio to the beginning of the retry loop
so it's set to NULL at one place.
Signed-off-by: Daniel Vacek <neelx@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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The use of ASSERT(0) is maybe useful for some cases but more like a
notice for developers. Assertions can be compiled in independently so
convert it to a debugging helper.
The difference is that it's just a warning and will not end up in BUG().
The converted cases are in connection with proper error handling.
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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Use the conditional warning instead of typing the whole condition.
Optional message is printed where it seems clear what could be the
problem.
Conversion is left out in btree_csum_one_bio() because of the additional
condition.
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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The bio implementation is not something we should really mess around,
and we shouldn't recalculate the pos from the folio over and over.
Instead just track then end of the current bio in logical file offsets
in the btrfs_bio_ctrl, which is much simpler and easier to read.
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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end_bbio_data_read() checks that each iterated folio fragment is aligned
and justifies that with block drivers advancing the bio. But block
driver only advance bi_iter, while end_bbio_data_read() uses
bio_for_each_folio_all() to iterate the immutable bi_io_vec array that
can't be changed by drivers at all.
Furthermore btrfs has already did the alignment check of the file
offset inside submit_one_sector(), and the size is fixed to fs block
size, there is no need to re-do the alignment check again inside the
endio function.
So just remove the unnecessary alignment check along with the incorrect
comment.
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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Rename all the exported functions from extent_map.h that don't have a
'btrfs_' prefix in their names, so that they are consistent with all the
other functions, to make it clear they are btrfs specific functions and
to avoid potential name collisions in the future with functions defined
elsewhere in the kernel.
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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These functions are exported and don't have a 'btrfs_' prefix in their
names, which goes against coding style conventions. Rename them to have
such prefix, making it clear they are from btrfs and avoiding potential
collisions in the future with functions defined elsewhere outside btrfs.
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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These functions are exported and don't have a 'btrfs_' prefix in their
names, which goes against coding style conventions. Rename them to have
such prefix, making it clear they are from btrfs and avoiding potential
collisions in the future with functions defined elsewhere outside btrfs.
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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These functions are exported and don't have a 'btrfs_' prefix in their
names, which goes against coding style conventions. Rename them to have
such prefix, making it clear they are from btrfs and avoiding potential
collisions in the future with functions defined elsewhere outside btrfs.
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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This is an exported function so it should have a 'btrfs_' prefix by
convention, to make it clear it's btrfs specific and to avoid collisions
with functions from elsewhere in the kernel.
Rename the function to add 'btrfs_' prefix to it.
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.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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These functions are exported so they should have a 'btrfs_' prefix by
convention, to make it clear they are btrfs specific and to avoid
collisions with functions from elsewhere in the kernel.
So add a 'btrfs_' prefix to their names to make it clear they are from
btrfs.
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.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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These functions are exported so they should have a 'btrfs_' prefix by
convention, to make it clear they are btrfs specific and to avoid
collisions with functions from elsewhere in the kernel. One of them has a
double underscore prefix which is also discouraged.
So remove double underscore prefix where applicable and add a 'btrfs_'
prefix to their name to make it clear they are from btrfs.
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.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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These functions are exported so they should have a 'btrfs_' prefix by
convention, to make it clear they are btrfs specific and to avoid
collisions with functions from elsewhere in the kernel. So add a prefix to
their name.
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.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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Currently we use the following pattern to detect if the folio contains
the end of a file:
if (folio->index == end_index)
folio_zero_range();
But that only works if the folio is page sized.
For the following case, it will not work and leave the range beyond EOF
uninitialized:
The page size is 4K, and the fs block size is also 4K.
16K 20K 24K
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EOF at 22K
And we have a large folio sized 8K at file offset 16K.
In that case, the old "folio->index == end_index" will not work, thus
the range [22K, 24K) will not be zeroed out.
Fix the following call sites which use the above pattern:
- add_ra_bio_pages()
- extent_writepage()
Reviewed-by: Filipe Manana <fdmanana@suse.com>
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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Inside functions unlock_delalloc_folio() and lock_delalloc_folios(), we
have the following early exits:
if (index == locked_folio->index && end_index == index)
return;
This allows us to exit early if the range is inside the same locked
folio.
However the current check relies on page sized folios, if we have a large
folio that contains @index but not at @index, then the early exit will
no longer trigger.
Furthermore without the above early check, the existing code can handle it
well, as both __process_folios_contig() and lock_delalloc_folios() will
skip any folio page lock/unlock if it's on the locked folio.
Here we remove the early exits and let the existing code handle the
same index case, to make the code a little simpler.
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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The function is doing an ASSERT() checking the folio order, but all
later functions are handling large folios properly, thus we can safely
remove that ASSERT().
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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Instead of using __clear_extent_bit() we can use clear_extent_bit() since
we pass a NULL value for the changeset argument.
Reviewed-by: Boris Burkov <boris@bur.io>
Reviewed-by: Qu Wenruo <wqu@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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Allow get_range_bits() to take an extent state pointer to pointer argument
so that we can cache the first extent state record in the target range, so
that a caller can use it for subsequent operations without doing a full
tree search. Currently the only user is try_release_extent_state(), which
then does a call to __clear_extent_bit() which can use such a cached state
record.
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 the release_folio callback (from struct address_space_operations) is
invoked we don't allow the folio to be released if its range is currently
locked in the inode's io_tree, as it may indicate the folio may be needed
by the task that locked the range.
However if the range is locked because an ordered extent is finishing,
then we can safely allow the folio to be released because ordered extent
completion doesn't need to use the folio at all.
When we are under memory pressure, the kernel starts writeback of dirty
pages (folios) with the goal of releasing the pages from the page cache
after writeback completes, however this often is not possible on btrfs
because:
* Once the writeback completes we queue the ordered extent completion;
* Once the ordered extent completion starts, we lock the range in the
inode's io_tree (at btrfs_finish_one_ordered());
* If the release_folio callback is called while the folio's range is
locked in the inode's io_tree, we don't allow the folio to be
released, so the kernel has to try to release memory elsewhere,
which may result in triggering more writeback or releasing other
pages from the page cache which may be more useful to have around
for applications.
In contrast, when the release_folio callback is invoked after writeback
finishes and before ordered extent completion starts or locks the range,
we allow the folio to be released, as well as when the release_folio
callback is invoked after ordered extent completion unlocks the range.
Improve on this by detecting if the range is locked for ordered extent
completion and if it is, allow the folio to be released. This detection
is achieved by adding a new extent flag in the io_tree that is set when
the range is locked during ordered extent completion.
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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Drop reference to pages from the comment since the function is fully folio
aware and works regardless of how many pages are in the folio. Also while
at it, capitalize the first word and make it more explicit that
release_folio is a callback from struct address_space_operations.
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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This flag is set after inserting the eb to the buffer tree and cleared
on it's removal. It was added in commit 34b41acec1ccc0 ("Btrfs: use a
bit to track if we're in the radix tree") and wanted to make use of it,
faa2dbf004e89e ("Btrfs: add sanity tests for new qgroup accounting
code"). Both are 10+ years old, we can remove the flag.
Signed-off-by: Daniel Vacek <neelx@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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This flag was added by commit 656f30dba7ab ("Btrfs: be aware of btree
inode write errors to avoid fs corruption") but it stopped being used
after commit 046b562b20a5 ("btrfs: use a separate end_io handler for
read_extent_buffer").
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Daniel Vacek <neelx@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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The folio_index() helper is only needed for mixed usage of page cache
and swap cache, for pure page cache usage, the caller can just use
folio->index instead.
It can't be a swap cache folio here. Swap mapping may only call into fs
through 'swap_rw' but btrfs does not use that method for swap.
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Kairui Song <kasong@tencent.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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When running machines with 64k page size and a 16k nodesize we started
seeing tree log corruption in production. This turned out to be because
we were not writing out dirty blocks sometimes, so this in fact affects
all metadata writes.
When writing out a subpage EB we scan the subpage bitmap for a dirty
range. If the range isn't dirty we do
bit_start++;
to move onto the next bit. The problem is the bitmap is based on the
number of sectors that an EB has. So in this case, we have a 64k
pagesize, 16k nodesize, but a 4k sectorsize. This means our bitmap is 4
bits for every node. With a 64k page size we end up with 4 nodes per
page.
To make this easier this is how everything looks
[0 16k 32k 48k ] logical address
[0 4 8 12 ] radix tree offset
[ 64k page ] folio
[ 16k eb ][ 16k eb ][ 16k eb ][ 16k eb ] extent buffers
[ | | | | | | | | | | | | | | | | ] bitmap
Now we use all of our addressing based on fs_info->sectorsize_bits, so
as you can see the above our 16k eb->start turns into radix entry 4.
When we find a dirty range for our eb, we correctly do bit_start +=
sectors_per_node, because if we start at bit 0, the next bit for the
next eb is 4, to correspond to eb->start 16k.
However if our range is clean, we will do bit_start++, which will now
put us offset from our radix tree entries.
In our case, assume that the first time we check the bitmap the block is
not dirty, we increment bit_start so now it == 1, and then we loop
around and check again. This time it is dirty, and we go to find that
start using the following equation
start = folio_start + bit_start * fs_info->sectorsize;
so in the case above, eb->start 0 is now dirty, and we calculate start
as
0 + 1 * fs_info->sectorsize = 4096
4096 >> 12 = 1
Now we're looking up the radix tree for 1, and we won't find an eb.
What's worse is now we're using bit_start == 1, so we do bit_start +=
sectors_per_node, which is now 5. If that eb is dirty we will run into
the same thing, we will look at an offset that is not populated in the
radix tree, and now we're skipping the writeout of dirty extent buffers.
The best fix for this is to not use sectorsize_bits to address nodes,
but that's a larger change. Since this is a fs corruption problem fix
it simply by always using sectors_per_node to increment the start bit.
Fixes: c4aec299fa8f ("btrfs: introduce submit_eb_subpage() to submit a subpage metadata page")
CC: stable@vger.kernel.org # 5.15+
Reviewed-by: Boris Burkov <boris@bur.io>
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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When we're handling folios from filemap, we can no longer assume all
folios are page sized.
Thus for call sites assuming the folio is page sized, change the
PAGE_SIZE usage to folio_size() instead.
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
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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Since we can no longer assume page sized folio for data filemap folios,
allow btrfs_alloc_subpage() to accept a new parameter, @fsize,
indicating the folio size.
This doesn't follow the regular behavior of passing a folio directly,
because this function is shared by both data and metadata folios, and
for metadata folios we have extra allocation policy to ensure no large
folios whose sizes are larger than nodesize (unless it's page sized).
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
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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To support large data folios, we can no longer assume every filemap
folio is page sized.
So btrfs_is_subpage() check must be done against a folio.
Thankfully for metadata folios, we have the full control and ensure a
large folio will not be large than nodesize, so
btrfs_meta_is_subpage() doesn't need this change.
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
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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The inline function btrfs_is_testing() is hardcoded to return 0 if
CONFIG_BTRFS_FS_RUN_SANITY_TESTS is not set. Currently we're relying on
the compiler optimizing out the call to alloc_test_extent_buffer() in
btrfs_find_create_tree_block(), as it's not been defined (it's behind an
#ifdef).
Add a stub version of alloc_test_extent_buffer() to avoid linker errors
on non-standard optimization levels. This problem was seen on GCC 14
with -O0 and is helps to see symbols that would be otherwise optimized
out.
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Mark Harmstone <maharmstone@fb.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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[OUT-OF-BAND DIRTY FOLIOS]
An out-of-band folio means the folio is marked dirty but without
notifying the filesystem.
This can lead to various problems, not limited to:
- No folio::private to track per block status
- No proper space reserved for such a dirty folio
[HISTORY IN BTRFS]
This used to be a problem related to get_user_page(), but with the
introduction of pin_user_pages*(), we should no longer hit such
case anymore.
In btrfs, we have a long history of catching such out-of-band dirty
folios by:
- Mark the folio ordered during delayed allocation
- Check the folio ordered flag during writeback
If the folio has no ordered flag, it means it doesn't go through
delayed allocation, thus it's definitely an out-of-band
one.
If we got one, we go through COW fixup, which will re-dirty the folio
with proper handling in another workqueue.
[PROBLEMS OF COW-FIXUP]
Such workaround is a blockage for us to migrate to iomap (it requires
extra flags to trace if a folio is dirtied by the fs or not) and I'd
argue it's not data checksum safe, since if a folio can be marked dirty
without informing the fs, the content can also change at any time.
But with the introduction of pin_user_pages*() during v5.8 merge
window, such out-of-band dirty folio such be treated as a bug.
Ext4 has treated such case by warning and erroring out even before
pin_user_pages*().
Furthermore, there are already proofs that such folio ordered flag
tracking can be screwed up by incorrect error handling, check the commit
messages of the following commits:
06f364284794 ("btrfs: do proper folio cleanup when cow_file_range() failed")
c2b47df81c8e ("btrfs: do proper folio cleanup when run_delalloc_nocow() failed")
[FIXES]
Unlike btrfs, ext4 and xfs (iomap) never bother handling such
out-of-band dirty folios.
- Ext4 just warns and errors out
- Iomap always follows the folio/block dirty flags
And there is nothing really COW specific, xfs also supports COW too.
Here we take one step towards ext4 by doing warning and erroring out.
But since the cow fixup thing is introduced from the beginning, we keep
the old behavior for non-experimental builds, and only do the new warning
for experimental builds before we're 100% sure and remove cow fixup.
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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[BUG]
Since the support of block size (sector size) < page size for btrfs,
test case generic/563 fails with 4K block size and 64K page size:
--- tests/generic/563.out 2024-04-25 18:13:45.178550333 +0930
+++ /home/adam/xfstests-dev/results//generic/563.out.bad 2024-09-30 09:09:16.155312379 +0930
@@ -3,7 +3,8 @@
read is in range
write is in range
write -> read/write
-read is in range
+read has value of 8388608
+read is NOT in range -33792 .. 33792
write is in range
...
[CAUSE]
The test case creates a 8MiB file, then does buffered write into the 8MiB
using 4K block size, to overwrite the whole file.
On 4K page sized systems, since the write range covers the full block and
page, btrfs will not bother reading the page, just like what XFS and EXT4
do.
But on 64K page sized systems, although the 4K sized write is still block
aligned, it's not page aligned anymore, thus btrfs will read the full
page, which will be accounted by cgroup and fail the test.
As the test case itself expects such 4K block aligned write should not
trigger any read.
Such expected behavior is an optimization to reduce folio reads when
possible, and unfortunately btrfs does not implement such optimization.
[FIX]
To skip the full page read, we need to do the following modification:
- Do not trigger full page read as long as the buffered write is block
aligned
This is pretty simple by modifying the check inside
prepare_uptodate_page().
- Skip already uptodate blocks during full page read
Or we can lead to the following data corruption:
0 32K 64K
|///////| |
Where the file range [0, 32K) is dirtied by buffered write, the
remaining range [32K, 64K) is not.
When reading the full page, since [0,32K) is only dirtied but not
written back, there is no data extent map for it, but a hole covering
[0, 64k).
If we continue reading the full page range [0, 64K), the dirtied range
will be filled with 0 (since there is only a hole covering the whole
range).
This causes the dirtied range to get lost.
With this optimization, btrfs can pass generic/563 even if the page size
is larger than fs block size.
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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