[PATCH v2 0/6] exfat: improve performance of NO_FAT_CHAIN to FAT_CHAIN conversion

[Chi Zhiling <chizhiling@163.com>]

From: Chi Zhiling <chizhiling@kylinos.cn>

This series improves the performance when converting files from NO_FAT_CHAIN
to FAT_CHAIN format (which happens when a file cannot allocate contiguous
clusters). It also adds proper error handling for FAT table write operations.

- Patch 1: Add block readahead for FAT blocks during conversion
- Patch 2-3: Refactor existing readahead code to use the new helper
- Patch 4: Remove redundant sec parameter from exfat_mirror_bh
- Patch 5: Cache buffer heads to reduce mark_buffer_dirty overhead
- Patch 6: Fix error handling to propagate FAT write errors to callers

Performance improvements for converting a 30GB file:

| Cluster Size | Before | After  | Speedup |
|--------------|--------|--------|---------|
| 512 bytes    | 47.667s| 1.866s | 25.5x   |
| 4KB          | 6.436s | 0.236s | 27.3x   |
| 32KB         | 0.758s | 0.034s | 22.3x   |
| 256KB        | 0.117s | 0.006s | 19.5x   |

v1: https://lore.kernel.org/all/20260204071435.602246-1-chizhiling@163.com/

Chi Zhiling (6):
  exfat: add block readahead in exfat_chain_cont_cluster
  exfat: use readahead helper in exfat_allocate_bitmap
  exfat: use readahead helper in exfat_get_dentry
  exfat: drop redundant sec parameter from exfat_mirror_bh
  exfat: optimize exfat_chain_cont_cluster with cached buffer heads
  exfat: fix error handling for FAT table operations

 fs/exfat/balloc.c   | 18 +++------
 fs/exfat/dir.c      | 52 +++++++------------------
 fs/exfat/exfat_fs.h | 13 +++++--
 fs/exfat/fatent.c   | 95 ++++++++++++++++++++++++++++++++++++---------
 fs/exfat/inode.c    |  5 ++-
 fs/exfat/misc.c     |  8 +++-
 fs/exfat/namei.c    |  3 +-
 7 files changed, 118 insertions(+), 76 deletions(-)

-- 
2.43.0