Re: [PATCH] shmem: make shmem default size a define value

[Qian Cai <cai@lca.pw>]

On Wed, 2019-10-09 at 13:17 -0700, -Gary- wrote:
> > > @@ -125,14 +128,14 @@ struct shmem_options {
> > >  #ifdef CONFIG_TMPFS
> > >  static unsigned long shmem_default_max_blocks(void)
> > >  {
> > > -	return totalram_pages() / 2;
> > > +	return SHMEM_SIZE_DEFAULT;
> > >  }
> > > 
> > >  static unsigned long shmem_default_max_inodes(void)
> > >  {
> > >  	unsigned long nr_pages = totalram_pages();
> > 
> > This is now unused.
> 
> Mind telling me what I missed, Qian?
> 
> I pulled from:
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
> 
> Latest commit is:
> 2019-10-08 15:36:04 -0700 e3280b54afed870d531571212f1fc375df39b7d2 Merge tag 'led-fixes-for-5.4-rc3' of git://git.kernel.org/pub/scm/linux/kernel/git/j.anaszewski/linux-leds
> 
> My patch is based on that, where the above code still exists, and nr_pages is still referenced below.  Apparently, it is making totalram_pages atomic, according to the commit that changed it:
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/diff/mm/shmem.c?id=ca79b0c211af63fa3276f0e3fd7dd9ada2439839
> 
> Should I be pulling from somewhere else, or also re-hacking nr_pages somehow?

Ah, you are right that nr_pages is still referenced, but then there could a
potentially out of sync? Would that be a problem? Is the compiler just smart
enough to call totalram_pages() only once?

CPU0:                                       CPU1:
unsigned long nr_pages = totalram_pages();
                                            totalram_pages_inc()
min(nr_pages - totalhigh_pages(), SHMEM_SIZE_DEFAULT);

> 
> -- Gary
> 
> > > -	return min(nr_pages - totalhigh_pages(), nr_pages / 2);
> > > +	return min(nr_pages - totalhigh_pages(), SHMEM_SIZE_DEFAULT);
> > >  }
> > >  #endif