Re: [PATCH v3 2/2] tmpfs: Make tmpfs scalable with percpu_counter for used blocks

[Andrew Morton <akpm@linux-foundation.org>]

On Fri, 18 Jun 2010 10:35:51 +0900 Minchan Kim <minchan.kim@gmail.com> wrote:

> > __struct shmem_sb_info {
> > __ __ __ __unsigned long max_blocks; __ /* How many blocks are allowed */
> > - __ __ __ unsigned long free_blocks; __/* How many are left for allocation */
> > + __ __ __ struct percpu_counter used_blocks; __/* How many are allocated */
> 
> Just a nitpick.
> Why do you change free_blocks and used_blocks?
> I think we can use free_blocks following as.
> 
> ex)
> if (percpu_counter_compare(&sbinfo->free_blocks, 0))

See previous lengthy discussion ;)

If we count free_blocks then we need to alter the value of free_blocks
in remount_fs, and reinitialising distributed counters on-the-fly is
ugly.

I suppose we could have done it by doing a large add or sub in
remount_fs, and keeping track of the exact value of free_blocks
elsewhere in the superblock, but it's far simpler this way.