Messages in this thread | | | Date | Fri, 26 Aug 2005 11:16:54 +1000 | From | Nick Piggin <> | Subject | Re: [PATCH] removes filp_count_lock and changes nr_files type to atomic_t |
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Eric Dumazet wrote:
> Furthermore, a lazy sync would mean to change sysctl proc_handler for > "file-nr" to perform a synchronize before calling proc_dointvec, this > would be really obscure. >
I was only using your terminology (ie. the 'lazy' synch after the atomic is updated).
Actually, a better idea would be to make a specific sysctl handler like Christoph said.
Unless you can show some improvement, it would better not to introduce the racy hack (even if it is mostly harmless).
>> Unless the fs people had a problem with that. >> >> And you may as well get rid of the atomic_inc_return which can be more >> expensive on some platforms and doesn't buy you much. >> atomic_inc; >> atomic_read; >> Should be enough if you don't care about lost updates here, yeah? >> > > You mean : > > atomic_inc(&counter); > lazeyvalue = atomic_read(&counter); > > instead of > > lazeyvalue = atomic_inc_return(&counter); >
Yes.
> In fact I couldnt find one architecture where the later would be more > expensive. >
atomic_inc_return guarantees a memory barrier, while the former statements do not. I'm fairly sure it will be more expensive on a POWER5.
-- SUSE Labs, Novell Inc.
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