RE: [PATCH] exfat: improve performance of exfat_free_cluster when using dirsync mount option

["Sungjong Seo" <sj1557.seo@samsung.com>]

> There are stressful update of cluster allocation bitmap when using dirsync
> mount option which is doing sync buffer on every cluster bit clearing.
> This could result in performance degradation when deleting big size file.
> Fix to update only when the bitmap buffer index is changed would make less
> disk access, improving performance especially for truncate operation.
> 
> Testing with Samsung 256GB sdcard, mounted with dirsync option (mount -t
> exfat /dev/block/mmcblk0p1 /temp/mount -o dirsync)
> 
> Remove 4GB file, blktrace result.
> [Before] : 39 secs.
> Total (blktrace):
>  Reads Queued:      0,        0KiB	 Writes Queued:      32775,
16387KiB
>  Read Dispatches:   0,        0KiB	 Write Dispatches:   32775,
16387KiB
>  Reads Requeued:    0		         Writes Requeued:        0
>  Reads Completed:   0,        0KiB	 Writes Completed:   32775,
16387KiB
>  Read Merges:       0,        0KiB	 Write Merges:           0,
0KiB
>  IO unplugs:        2        	     Timer unplugs:          0
> 
> [After] : 1 sec.
> Total (blktrace):
>  Reads Queued:      0,        0KiB	 Writes Queued:         13,
6KiB
>  Read Dispatches:   0,        0KiB	 Write Dispatches:      13,
6KiB
>  Reads Requeued:    0		         Writes Requeued:        0
>  Reads Completed:   0,        0KiB	 Writes Completed:      13,
6KiB
>  Read Merges:       0,        0KiB	 Write Merges:           0,
0KiB
>  IO unplugs:        1        	     Timer unplugs:          0
> 
> Signed-off-by: Hyeongseok Kim <hyeongseok@gmail.com>

Looks good.
Thanks for your work!

Acked-by: Sungjong Seo <sj1557.seo@samsung.com>