[PATCH v2 0/1] exfat: reduce directory scans during file creation

[PATCH v2 0/1] exfat: reduce directory scans during file creation

[Yang Wen]

Creating files in a large exfat directory may require repeated linear
directory scans.

After an empty-entry hint is used successfully, the remaining
contiguous empty entries are not retained for the next create operation.
This can cause subsequent operations to rediscover available directory
space.

In a test creating 20,000 files with random names and sizes between 1 KiB
and 4 KiB in one directory, the elapsed time changed as follows:

  Before: 3879 seconds
  After:  3050 seconds

---

Changes since v1:
- Drop the LOOKUP_CREATE negative dentry change.
- Make exfat_cache_next_empty_entry() return void and skip caching if
  exfat_chain_advance() fails.

Yang Wen (1):
  exfat: preserve the next empty-entry hint after allocation

 fs/exfat/namei.c | 39 +++++++++++++++++++++++++++++++++++++--
 1 file changed, 37 insertions(+), 2 deletions(-)

-- 
2.34.1

RE: [PATCH v2 0/1] exfat: reduce directory scans during file creation

[Sungjong Seo]

> Creating files in a large exfat directory may require repeated linear
> directory scans.
> 
> After an empty-entry hint is used successfully, the remaining contiguous
> empty entries are not retained for the next create operation.
> This can cause subsequent operations to rediscover available directory
> space.
> 
> In a test creating 20,000 files with random names and sizes between 1 KiB
> and 4 KiB in one directory, the elapsed time changed as follows:
> 
>   Before: 3879 seconds
>   After:  3050 seconds
Hello, Yang Wen,

As Namjae reviewed, we intentionally drop the dentry in LOOKUP_CREATE to
maintain the case of newly created filenames. Therefore, when creating
a new file, a brute-force search of the entire directory is required,
and the hint value is naturally updated during this process.

For this reason, I believe this current patch will not improve performance
and is an unnecessary operation. Is there any performance gain with the
current patch, excluding the dropped part?

> 
> ---
> 
> Changes since v1:
> - Drop the LOOKUP_CREATE negative dentry change.
> - Make exfat_cache_next_empty_entry() return void and skip caching if
>   exfat_chain_advance() fails.
> 
> Yang Wen (1):
>   exfat: preserve the next empty-entry hint after allocation
> 
>  fs/exfat/namei.c | 39 +++++++++++++++++++++++++++++++++++++--
>  1 file changed, 37 insertions(+), 2 deletions(-)
> 
> --
> 2.34.1