[Devel] Re: [PATCH] memory.min_usage (seqlock for res_counter)

[KAMEZAWA Hiroyuki]

On Tue, 04 Dec 2007 14:10:42 +0300
Pavel Emelyanov <xemul at openvz.org> wrote:

> KAMEZAWA Hiroyuki wrote:
> > This is seqlock version res_counter.
> > Maybe this this will reduce # of spin_lock.
> > 
> > Pavel-san, How about this ?
> 
> AFAIS the readlock is used only in the check_under_limit(),
> but I think, that even if we read usage and limit values
> in this case non-atomically, this won't result in any 
> dramatic sequence at all. No?
> 
Reader can detect *any* changes in res_counter member which happens
while they access res_counter between seq_begin/seq_retry.
Memory barrier and "sequence" of seq_lock guarantees this.
So..there is no dramatical situation.
(it's used for accesing xtime.)

I'm sorry if I miss your point.

Thanks,
-Kame

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