linux-kernel - [PATCH 0/3] btrfs: Replace kmap() with kmap_local

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Message-Id: <20220531145335.13954-1-fmdefrancesco@gmail.com>
Date:   Tue, 31 May 2022 16:53:32 +0200
From:   "Fabio M. De Francesco" <fmdefrancesco@...il.com>
To:     Chris Mason <clm@...com>, Josef Bacik <josef@...icpanda.com>,
        David Sterba <dsterba@...e.com>,
        Ira Weiny <ira.weiny@...el.com>, linux-btrfs@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     "Fabio M. De Francesco" <fmdefrancesco@...il.com>
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(-)

-- 
2.36.1