erofs: fold in z_erofs_decompress()

No need this helper since it's just a simple wrapper for decompress
method and only one caller. So, let's fold in directly instead.

Signed-off-by: Yue Hu <huyue

erofs: fold in z_erofs_decompress()

No need this helper since it's just a simple wrapper for decompress
method and only one caller. So, let's fold in directly instead.

Signed-off-by: Yue Hu <huyue2@coolpad.com>
Reviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/20230426084449.12781-1-zbestahu@gmail.com
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>

show more ...

erofs: use HIPRI by default if per-cpu kthreads are enabled

As Sandeep shown [1], high priority RT per-cpu kthreads are
typically helpful for Android scenarios to minimize the scheduling
latencies.

erofs: use HIPRI by default if per-cpu kthreads are enabled

As Sandeep shown [1], high priority RT per-cpu kthreads are
typically helpful for Android scenarios to minimize the scheduling
latencies.

Switch EROFS_FS_PCPU_KTHREAD_HIPRI on by default if
EROFS_FS_PCPU_KTHREAD is on since it's the typical use cases for
EROFS_FS_PCPU_KTHREAD.

Also clean up unneeded sched_set_normal().

[1] https://lore.kernel.org/r/CAB=BE-SBtO6vcoyLNA9F-9VaN5R0t3o_Zn+FW8GbO6wyUqFneQ@mail.gmail.com

Reviewed-by: Yue Hu <huyue2@coolpad.com>
Reviewed-by: Sandeep Dhavale <dhavale@google.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/20230522092141.124290-1-hsiangkao@linux.alibaba.com

show more ...

erofs: sunset erofs_dbg()

Such debug messages are rarely used now. Let's get rid of these,
and revert locally if they are needed for debugging.

Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.co

erofs: sunset erofs_dbg()

Such debug messages are rarely used now. Let's get rid of these,
and revert locally if they are needed for debugging.

Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Link: https://lore.kernel.org/r/20230414083027.12307-1-hsiangkao@linux.alibaba.com

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erofs: keep meta inode into erofs_buf

So that erofs_read_metadata() can read metadata from other inodes
(e.g. packed inode) as well.

Signed-off-by: Jingbo Xu <jefflexu@linux.alibaba.com>
Acked-by:

erofs: keep meta inode into erofs_buf

So that erofs_read_metadata() can read metadata from other inodes
(e.g. packed inode) as well.

Signed-off-by: Jingbo Xu <jefflexu@linux.alibaba.com>
Acked-by: Chao Yu <chao@kernel.org>
Link: https://lore.kernel.org/r/20230407141710.113882-2-jefflexu@linux.alibaba.com
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>

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erofs: avoid hardcoded blocksize for subpage block support

As the first step of converting hardcoded blocksize to that specified in
on-disk superblock, convert all call sites of hardcoded blocksize

erofs: avoid hardcoded blocksize for subpage block support

As the first step of converting hardcoded blocksize to that specified in
on-disk superblock, convert all call sites of hardcoded blocksize to
sb->s_blocksize except for:

1) use sbi->blkszbits instead of sb->s_blocksize in
erofs_superblock_csum_verify() since sb->s_blocksize has not been
updated with the on-disk blocksize yet when the function is called.

2) use inode->i_blkbits instead of sb->s_blocksize in erofs_bread(),
since the inode operated on may be an anonymous inode in fscache mode.
Currently the anonymous inode is allocated from an anonymous mount
maintained in erofs, while in the near future we may allocate anonymous
inodes from a generic API directly and thus have no access to the
anonymous inode's i_sb. Thus we keep the block size in i_blkbits for
anonymous inodes in fscache mode.

Be noted that this patch only gets rid of the hardcoded blocksize, in
preparation for actually setting the on-disk block size in the following
patch. The hard limit of constraining the block size to PAGE_SIZE still
exists until the next patch.

Signed-off-by: Jingbo Xu <jefflexu@linux.alibaba.com>
Reviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Reviewed-by: Yue Hu <huyue2@coolpad.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Link: https://lore.kernel.org/r/20230313135309.75269-2-jefflexu@linux.alibaba.com
[ Gao Xiang: fold a patch to fix incorrect truncated offsets. ]
Link: https://lore.kernel.org/r/20230413035734.15457-1-zhujia.zj@bytedance.com
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>

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erofs: Revert "erofs: fix kvcalloc() misuse with __GFP_NOFAIL"

Let's revert commit 12724ba38992 ("erofs: fix kvcalloc() misuse with
__GFP_NOFAIL") since kvmalloc() already supports __GFP_NOFAIL in c

erofs: Revert "erofs: fix kvcalloc() misuse with __GFP_NOFAIL"

Let's revert commit 12724ba38992 ("erofs: fix kvcalloc() misuse with
__GFP_NOFAIL") since kvmalloc() already supports __GFP_NOFAIL in commit
a421ef303008 ("mm: allow !GFP_KERNEL allocations for kvmalloc"). So
the original fix was wrong.

Actually there was some issue as [1] discussed, so before that mm fix
is landed, the warn could still happen but applying this commit first
will cause less.

[1] https://lore.kernel.org/r/20230305053035.1911-1-hsiangkao@linux.alibaba.com

Fixes: 12724ba38992 ("erofs: fix kvcalloc() misuse with __GFP_NOFAIL")
Reviewed-by: Chao Yu <chao@kernel.org>
Link: https://lore.kernel.org/r/20230309053148.9223-1-hsiangkao@linux.alibaba.com
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>

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erofs: fix an error code in z_erofs_init_zip_subsystem()

Return -ENOMEM if alloc_workqueue() fails. Don't return success.

Fixes: d8a650adf429 ("erofs: add per-cpu threads for decompression as an o

erofs: fix an error code in z_erofs_init_zip_subsystem()

Return -ENOMEM if alloc_workqueue() fails. Don't return success.

Fixes: d8a650adf429 ("erofs: add per-cpu threads for decompression as an option")
Signed-off-by: Dan Carpenter <error27@gmail.com>
Reviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/Y+4d0FRsUq8jPoOu@kili
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>

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erofs: add per-cpu threads for decompression as an option

Using per-cpu thread pool we can reduce the scheduling latency compared
to workqueue implementation. With this patch scheduling latency and

erofs: add per-cpu threads for decompression as an option

Using per-cpu thread pool we can reduce the scheduling latency compared
to workqueue implementation. With this patch scheduling latency and
variation is reduced as per-cpu threads are high priority kthread_workers.

The results were evaluated on arm64 Android devices running 5.10 kernel.

The table below shows resulting improvements of total scheduling latency
for the same app launch benchmark runs with 50 iterations. Scheduling
latency is the latency between when the task (workqueue kworker vs
kthread_worker) became eligible to run to when it actually started
running.
+-------------------------+-----------+----------------+---------+
| | workqueue | kthread_worker | diff |
+-------------------------+-----------+----------------+---------+
| Average (us) | 15253 | 2914 | -80.89% |
| Median (us) | 14001 | 2912 | -79.20% |
| Minimum (us) | 3117 | 1027 | -67.05% |
| Maximum (us) | 30170 | 3805 | -87.39% |
| Standard deviation (us) | 7166 | 359 | |
+-------------------------+-----------+----------------+---------+

Background: Boot times and cold app launch benchmarks are very
important to the Android ecosystem as they directly translate to
responsiveness from user point of view. While EROFS provides
a lot of important features like space savings, we saw some
performance penalty in cold app launch benchmarks in few scenarios.
Analysis showed that the significant variance was coming from the
scheduling cost while decompression cost was more or less the same.

Having per-cpu thread pool we can see from the above table that this
variation is reduced by ~80% on average. This problem was discussed
at LPC 2022. Link to LPC 2022 slides and talk at [1]

[1] https://lpc.events/event/16/contributions/1338/

[ Gao Xiang: At least, we have to add this until WQ_UNBOUND workqueue
issue [2] on many arm64 devices is resolved. ]
[2] https://lore.kernel.org/r/CAJkfWY490-m6wNubkxiTPsW59sfsQs37Wey279LmiRxKt7aQYg@mail.gmail.com

Signed-off-by: Sandeep Dhavale <dhavale@google.com>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/20230208093322.75816-1-hsiangkao@linux.alibaba.com

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erofs: move zdata.h into zdata.c

Definitions in zdata.h are only used in zdata.c and for internal
use only. No logic changes.

Reviewed-by: Yue Hu <huyue2@coolpad.com>
Reviewed-by: Chao Yu <chao@ke

erofs: move zdata.h into zdata.c

Definitions in zdata.h are only used in zdata.c and for internal
use only. No logic changes.

Reviewed-by: Yue Hu <huyue2@coolpad.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/20230204093040.97967-4-hsiangkao@linux.alibaba.com

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erofs: remove tagged pointer helpers

Just open-code the remaining one to simplify the code.

Reviewed-by: Yue Hu <huyue2@coolpad.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Gao Xiang

erofs: remove tagged pointer helpers

Just open-code the remaining one to simplify the code.

Reviewed-by: Yue Hu <huyue2@coolpad.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/20230204093040.97967-3-hsiangkao@linux.alibaba.com

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erofs: avoid tagged pointers to mark sync decompression

We could just use a boolean in z_erofs_decompressqueue for sync
decompression to simplify the code.

Reviewed-by: Yue Hu <huyue2@coolpad.com>

erofs: avoid tagged pointers to mark sync decompression

We could just use a boolean in z_erofs_decompressqueue for sync
decompression to simplify the code.

Reviewed-by: Yue Hu <huyue2@coolpad.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/20230204093040.97967-2-hsiangkao@linux.alibaba.com

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erofs: fix kvcalloc() misuse with __GFP_NOFAIL

As reported by syzbot [1], kvcalloc() cannot work with __GFP_NOFAIL.
Let's use kcalloc() instead.

[1] https://lore.kernel.org/r/0000000000007796bd05f

erofs: fix kvcalloc() misuse with __GFP_NOFAIL

As reported by syzbot [1], kvcalloc() cannot work with __GFP_NOFAIL.
Let's use kcalloc() instead.

[1] https://lore.kernel.org/r/0000000000007796bd05f1852ec2@google.com

Reported-by: syzbot+c3729cda01706a04fb98@syzkaller.appspotmail.com
Fixes: fe3e5914e6dc ("erofs: try to leave (de)compressed_pages on stack if possible")
Fixes: 4f05687fd703 ("erofs: introduce struct z_erofs_decompress_backend")
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/20230110074927.41651-1-hsiangkao@linux.alibaba.com

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erofs: Fix pcluster memleak when its block address is zero

syzkaller reported a memleak:
https://syzkaller.appspot.com/bug?id=62f37ff612f0021641eda5b17f056f1668aa9aed

unreferenced object 0xffff8881

erofs: Fix pcluster memleak when its block address is zero

syzkaller reported a memleak:
https://syzkaller.appspot.com/bug?id=62f37ff612f0021641eda5b17f056f1668aa9aed

unreferenced object 0xffff88811009c7f8 (size 136):
...
backtrace:
[<ffffffff821db19b>] z_erofs_do_read_page+0x99b/0x1740
[<ffffffff821dee9e>] z_erofs_readahead+0x24e/0x580
[<ffffffff814bc0d6>] read_pages+0x86/0x3d0
...

syzkaller constructed a case: in z_erofs_register_pcluster(),
ztailpacking = false and map->m_pa = zero. This makes pcl->obj.index be
zero although pcl is not a inline pcluster.

Then following path adds refcount for grp, but the refcount won't be put
because pcl is inline.

z_erofs_readahead()
z_erofs_do_read_page() # for another page
z_erofs_collector_begin()
erofs_find_workgroup()
erofs_workgroup_get()

Since it's illegal for the block address of a non-inlined pcluster to
be zero, add check here to avoid registering the pcluster which would
be leaked.

Fixes: cecf864d3d76 ("erofs: support inline data decompression")
Reported-by: syzbot+6f8cd9a0155b366d227f@syzkaller.appspotmail.com
Signed-off-by: Chen Zhongjin <chenzhongjin@huawei.com>
Reviewed-by: Yue Hu <huyue2@coolpad.com>
Reviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Link: https://lore.kernel.org/r/Y42Kz6sVkf+XqJRB@debian
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>

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erofs: clean up cached I/O strategies

After commit 4c7e42552b3a ("erofs: remove useless cache strategy of
DELAYEDALLOC"), only one cached I/O allocation strategy is supported:

When cached I/O is

erofs: clean up cached I/O strategies

After commit 4c7e42552b3a ("erofs: remove useless cache strategy of
DELAYEDALLOC"), only one cached I/O allocation strategy is supported:

When cached I/O is preferred, page allocation is applied without
direct reclaim. If allocation fails, fall back to inplace I/O.

Let's get rid of z_erofs_cache_alloctype. No logical changes.

Reviewed-by: Yue Hu <huyue2@coolpad.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Yue Hu <huyue2@coolpad.com>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/20221206060352.152830-1-xiang@kernel.org

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fs: fix leaked psi pressure state

When psi annotations were added to to btrfs compression reads, the psi
state tracking over add_ra_bio_pages and btrfs_submit_compressed_read was
faulty. A pressure

fs: fix leaked psi pressure state

When psi annotations were added to to btrfs compression reads, the psi
state tracking over add_ra_bio_pages and btrfs_submit_compressed_read was
faulty. A pressure state, once entered, is never left. This results in
incorrectly elevated pressure, which triggers OOM kills.

pflags record the *previous* memstall state when we enter a new one. The
code tried to initialize pflags to 1, and then optimize the leave call
when we either didn't enter a memstall, or were already inside a nested
stall. However, there can be multiple PageWorkingset pages in the bio, at
which point it's that path itself that enters repeatedly and overwrites
pflags. This causes us to miss the exit.

Enter the stall only once if needed, then unwind correctly.

erofs has the same problem, fix that up too. And move the memstall exit
past submit_bio() to restore submit accounting originally added by
b8e24a9300b0 ("block: annotate refault stalls from IO submission").

Link: https://lkml.kernel.org/r/Y2UHRqthNUwuIQGS@cmpxchg.org
Fixes: 4088a47e78f9 ("btrfs: add manual PSI accounting for compressed reads")
Fixes: 99486c511f68 ("erofs: add manual PSI accounting for the compressed address space")
Fixes: 118f3663fbc6 ("block: remove PSI accounting from the bio layer")
Link: https://lore.kernel.org/r/d20a0a85-e415-cf78-27f9-77dd7a94bc8d@leemhuis.info/
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Reported-by: Thorsten Leemhuis <linux@leemhuis.info>
Tested-by: Thorsten Leemhuis <linux@leemhuis.info>
Cc: Chao Yu <chao@kernel.org>
Cc: Chris Mason <clm@fb.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: David Sterba <dsterba@suse.com>
Cc: Gao Xiang <xiang@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Josef Bacik <josef@toxicpanda.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

show more ...

erofs: fix general protection fault when reading fragment

As syzbot reported [1], the fragment feature sb flag is not set, so
packed_inode != NULL needs to be checked in z_erofs_read_fragment().

[1

erofs: fix general protection fault when reading fragment

As syzbot reported [1], the fragment feature sb flag is not set, so
packed_inode != NULL needs to be checked in z_erofs_read_fragment().

[1] https://lore.kernel.org/all/0000000000002e7a8905eb841ddd@google.com/

Reported-by: syzbot+3faecbfd845a895c04cb@syzkaller.appspotmail.com
Fixes: b15b2e307c3a ("erofs: support on-disk compressed fragments data")
Signed-off-by: Yue Hu <huyue2@coolpad.com>
Reviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Link: https://lore.kernel.org/r/20221021085325.25788-1-zbestahu@gmail.com
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>

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erofs: fix up inplace decompression success rate

Partial decompression should be checked after updating length.
It's a new regression when introducing multi-reference pclusters.

Fixes: 2bfab9c0edac

erofs: fix up inplace decompression success rate

Partial decompression should be checked after updating length.
It's a new regression when introducing multi-reference pclusters.

Fixes: 2bfab9c0edac ("erofs: record the longest decompressed size in this round")
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/20221014064915.8103-1-hsiangkao@linux.alibaba.com

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erofs: shouldn't churn the mapping page for duplicated copies

If other duplicated copies exist in one decompression shot, should
leave the old page as is rather than replace it with the new duplicat

erofs: shouldn't churn the mapping page for duplicated copies

If other duplicated copies exist in one decompression shot, should
leave the old page as is rather than replace it with the new duplicated
one. Otherwise, the following cold path to deal with duplicated copies
will use the invalid bvec. It impacts compressed data deduplication.

Also, shift the onlinepage EIO bit to avoid touching the signed bit.

Fixes: 267f2492c8f7 ("erofs: introduce multi-reference pclusters (fully-referenced)")
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/20221012045056.13421-1-hsiangkao@linux.alibaba.com

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erofs: introduce partial-referenced pclusters

Due to deduplication for compressed data, pclusters can be partially
referenced with their prefixes.

Together with the user-space implementation, it en

erofs: introduce partial-referenced pclusters

Due to deduplication for compressed data, pclusters can be partially
referenced with their prefixes.

Together with the user-space implementation, it enables EROFS
variable-length global compressed data deduplication with rolling
hash.

Link: https://lore.kernel.org/r/20220923014915.4362-1-hsiangkao@linux.alibaba.com
Reviewed-by: Yue Hu <huyue2@coolpad.com>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>

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erofs: support on-disk compressed fragments data

Introduce on-disk compressed fragments data feature.

This approach adds a new field called `h_fragmentoff' in the per-file
compression header to ind

erofs: support on-disk compressed fragments data

Introduce on-disk compressed fragments data feature.

This approach adds a new field called `h_fragmentoff' in the per-file
compression header to indicate the fragment offset of each tail pcluster
or the whole file in the special packed inode.

Similar to ztailpacking, it will also find and record the 'headlcn'
of the tail pcluster when initializing per-inode zmap for making
follow-on requests more easy.

Signed-off-by: Yue Hu <huyue2@coolpad.com>
Reviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/YzHKxcFTlHGgXeH9@B-P7TQMD6M-0146.local
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>

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erofs: add manual PSI accounting for the compressed address space

erofs uses an additional address space for compressed data read from disk
in addition to the one directly associated with the inode.

erofs: add manual PSI accounting for the compressed address space

erofs uses an additional address space for compressed data read from disk
in addition to the one directly associated with the inode. Reading into
the lower address space is open coded using add_to_page_cache_lru instead
of using the filemap.c helper for page allocation micro-optimizations,
which means it is not covered by the MM PSI annotations for ->read_folio
and ->readahead, so add manual ones instead.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/20220915094200.139713-5-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>

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erofs: introduce multi-reference pclusters (fully-referenced)

Let's introduce multi-reference pclusters at runtime. In details,
if one pcluster is requested by multiple extents at almost the same
ti

erofs: introduce multi-reference pclusters (fully-referenced)

Let's introduce multi-reference pclusters at runtime. In details,
if one pcluster is requested by multiple extents at almost the same
time (even belong to different files), the longest extent will be
decompressed as representative and the other extents are actually
copied from the longest one in one round.

After this patch, fully-referenced extents can be correctly handled
and the full decoding check needs to be bypassed for
partial-referenced extents.

Acked-by: Chao Yu <chao@kernel.org>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/20220715154203.48093-17-hsiangkao@linux.alibaba.com

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erofs: record the longest decompressed size in this round

Currently, `pcl->length' records the longest decompressed length
as long as the pcluster itself isn't reclaimed. However, such
number is un

erofs: record the longest decompressed size in this round

Currently, `pcl->length' records the longest decompressed length
as long as the pcluster itself isn't reclaimed. However, such
number is unneeded for the general cases since it doesn't indicate
the exact decompressed size in this round.

Instead, let's record the decompressed size for this round instead,
thus `pcl->nr_pages' can be completely dropped and pageofs_out is
also designed to be kept in sync with `pcl->length'.

Acked-by: Chao Yu <chao@kernel.org>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/20220715154203.48093-16-hsiangkao@linux.alibaba.com

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erofs: introduce z_erofs_do_decompressed_bvec()

Both out_bvecs and in_bvecs share the common logic for decompressed
buffers. So let's make a helper for this.

Acked-by: Chao Yu <chao@kernel.org>
Sig

erofs: introduce z_erofs_do_decompressed_bvec()

Both out_bvecs and in_bvecs share the common logic for decompressed
buffers. So let's make a helper for this.

Acked-by: Chao Yu <chao@kernel.org>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/20220715154203.48093-15-hsiangkao@linux.alibaba.com

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erofs: try to leave (de)compressed_pages on stack if possible

For the most cases, small pclusters can be decompressed with page
arrays on stack.

Try to leave both (de)compressed_pages on stack if p

erofs: try to leave (de)compressed_pages on stack if possible

For the most cases, small pclusters can be decompressed with page
arrays on stack.

Try to leave both (de)compressed_pages on stack if possible as before.

Acked-by: Chao Yu <chao@kernel.org>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/20220715154203.48093-14-hsiangkao@linux.alibaba.com

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