Re: [PATCH 2/8] cgroup: kill CSS_REMOVED

[Kamezawa Hiroyuki <kamezawa.hiroyu-+CUm20s59erQFUHtdCDX3A@public.gmane.org>]

(2012/10/31 13:22), Tejun Heo wrote:
> CSS_REMOVED is one of the several contortions which were necessary to
> support css reference draining on cgroup removal.  All css->refcnts
> which need draining should be deactivated and verified to equal zero
> atomically w.r.t. css_tryget().  If any one isn't zero, all refcnts
> needed to be re-activated and css_tryget() shouldn't fail in the
> process.
> 
> This was achieved by letting css_tryget() busy-loop until either the
> refcnt is reactivated (failed removal attempt) or CSS_REMOVED is set
> (committing to removal).
> 
> Now that css refcnt draining is no longer used, there's no need for
> atomic rollback mechanism.  css_tryget() simply can look at the
> reference count and fail if the it's deactivated - it's never getting
> re-activated.
> 
> This patch removes CSS_REMOVED and updates __css_tryget() to fail if
> the refcnt is deactivated.
> 
> Note that this removes css_is_removed() whose only user is VM_BUG_ON()
> in memcontrol.c.  We can replace it with a check on the refcnt but
> given that the only use case is a debug assert, I think it's better to
> simply unexport it.
> 
> Signed-off-by: Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
> Cc: Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>
> Cc: Michal Hocko <mhocko-AlSwsSmVLrQ@public.gmane.org>
> Cc: Balbir Singh <bsingharora-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu-+CUm20s59erQFUHtdCDX3A@public.gmane.org>

Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu-+CUm20s59erQFUHtdCDX3A@public.gmane.org>