Re: [PATCH v3 0/3] exfat: speed up file creation in large directories

[Chi Zhiling]

On 9/2/26 11:24 PM, Yang Wen wrote:
> Negative name lookups and empty-entry allocation can repeatedly scan a
> directory from the beginning. Bulk creation in a large directory therefore
> approaches O(N^2).
>
> This series separates the optimization into three independently reviewable
> steps. Patch 1 adds the Bloom filter used to reject definite name misses.
> Patch 2 retains and correctly invalidates the next-empty-entry hint. Patch 3
> adds the LRU and shrinker used to reclaim filters under memory pressure.
>
> Test environment:
>    QEMU TCG multi-thread, 4 vCPUs, 6 GiB RAM
>    4 GiB exFAT image, 32 KiB clusters
>
> Creating 20,000 empty files improved from 589.48 seconds to 5.33 seconds,
> which is a 110.6-fold speedup.
>
> Changes in v3:
> - Split the change into Bloom filter, empty-entry hint, and shrinker patches.
> - Accept filenames containing exactly 255 UTF-16 code units while building
>    the Bloom filter.
> - Invalidate the empty-entry hint in every path that can free directory
>    entries, preventing stale hints from skipping earlier holes.
>
> Changes in v2:
> - Move exfat_name_filter_free() to exfat_evict_inode() because
>    ->free_inode() may run from an RCU callback in softirq context.
>
> Yang Wen (3):
>    exfat: add a Bloom filter for negative name lookups
>    exfat: retain the next empty directory entry hint
>    exfat: reclaim name filters under memory pressure
>
>   fs/exfat/dir.c      | 279 ++++++++++++++++++++++++++++++++++++++++++++
>   fs/exfat/exfat_fs.h |  23 ++++
>   fs/exfat/inode.c    |   1 +
>   fs/exfat/namei.c    |  58 ++++++++-
>   fs/exfat/super.c    |   9 ++
>   5 files changed, 369 insertions(+), 1 deletion(-)

This is a much better version than v2.

Reviewed-by: Chi Zhiling <chizhiling@xxxxxxxxxx>

Thanks!