Messages in this thread | | | Date | Tue, 6 Oct 2009 18:03:33 +0100 | From | Mel Gorman <> | Subject | Re: [this_cpu_xx V4 13/20] this_cpu_ops: page allocator conversion |
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On Tue, Oct 06, 2009 at 12:34:56PM -0400, Christoph Lameter wrote: > On Tue, 6 Oct 2009, Mel Gorman wrote: > > > > - local_irq_save(flags); > > > - pcp = &this_cpu_ptr(zone->pageset)->pcp; > > > migratetype = get_pageblock_migratetype(page); > > > set_page_private(page, migratetype); > > > if (unlikely(wasMlocked)) > > > > Why did you move local_irq_save() ? It should have stayed where it was > > because VM counters are updated under the lock. Only the this_cpu_ptr > > should be moving. > > The __count_vm_event()?
and the __dec_zone_page_state within free_page_mlock(). However, it's already atomic so it shouldn't be a problem.
> VM counters may be incremented in a racy way if > convenient. x86 usually produces non racy code (and with this patchset > will always produce non racy code) but f.e. IA64 has always had racy > updates. I'd rather shorted the irq off section. >
The count_vm_event is now racier than it was and no longer symmetric with the PGALLOC counting which still happens with IRQs disabled. The assymetry could look very strange if there are a lot more frees than allocs for example because the raciness between the counters is difference.
While I have no problem as such with the local_irq_save() moving (although I would like PGFREE and PGALLOC to be accounted both with or without IRQs enabled), I think it deserves to be in a patch all to itself and not hidden in an apparently unrelated change.
> See the comment in vmstat.h. >
-- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab
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