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Subject[PATCH 0/3] btrfs: Replace kmap() with kmap_local_page()
This is the first series of patches aimed towards the conversion of Btrfs
filesystem from the use of kmap() to kmap_local_page().

The use of kmap() is being deprecated in favor of kmap_local_page() where
it is feasible. With kmap_local_page() the mapping is per thread, CPU
local and not globally visible.

Therefore, use kmap_local_page() / kunmap_local() in Btrfs wherever the
mappings are per thread and not globally visible.

Tested on QEMU + KVM 32 bits VM with 4GB of RAM and HIGHMEM64G enabled.

tweed32:~ # uname -a
Linux tweed32 5.18.0-torvalds-debug-x86_32+ #2 SMP PREEMPT_DYNAMIC Tue \
May 31 15:20:07 CEST 2022 i686 athlon i386 GNU/Linux

tweed32:~ # btrfs check -p ~zoek/dev/btrfs.file
Opening filesystem to check...
Checking filesystem on /home/zoek/dev/btrfs.file
UUID: 897d65c5-1167-45b4-b811-2bfe74a320ca
[1/7] checking root items (0:00:00 elapsed, 1774 items checked)
[2/7] checking extents (0:00:00 elapsed, 135 items checked)
[3/7] checking free space tree (0:00:00 elapsed, 4 items checked)
[4/7] checking fs roots (0:00:00 elapsed, 104 items checked)
[5/7] checking csums (without verifying data) (0:00:00 elapsed, 205 items checked)
[6/7] checking root refs (0:00:00 elapsed, 3 items checked)
[7/7] checking quota groups skipped (not enabled on this FS)
found 47394816 bytes used, no error found
total csum bytes: 44268
total tree bytes: 2064384
total fs tree bytes: 1720320
total extent tree bytes: 180224
btree space waste bytes: 465350
file data blocks allocated: 45330432
referenced 45330432

Fabio M. De Francesco (3):
btrfs: Replace kmap() with kmap_local_page() in inode.c
btrfs: Replace kmap() with kmap_local_page() in lzo.c
btrfs: Replace kmap() with kmap_local_page() in zlib.c

fs/btrfs/inode.c | 6 +++---
fs/btrfs/lzo.c | 28 ++++++++++++----------------
fs/btrfs/zlib.c | 40 ++++++++++++++++++++--------------------
3 files changed, 35 insertions(+), 39 deletions(-)


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