Messages in this thread | | | Date | Thu, 1 Apr 2010 18:18:40 +0200 | From | Andrea Arcangeli <> | Subject | Re: [COUNTERPATCH] mm: avoid overflowing preempt_count() in mmu_take_all_locks() |
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On Thu, Apr 01, 2010 at 06:12:34PM +0200, Peter Zijlstra wrote: > One thing we can do there is to mutex_trylock() if we get the lock, see > if we've got the right object, if the trylock fails we can do the > refcount thing and sleep. That would allow the fast-path to remain a > single atomic.
But then how do you know which anon_vma_unlink has to decrease the refcount and which not? That info should need to be stored in the kernel stack, can't be stored in the vma. I guess it's feasible but passing that info around sounds more tricky than the trylock itself (adding params to those functions with int &refcount).
> The only thing is growing that anon_vma struct, but KSM seems to already > do that for the most common .configs.
Ok, from my initial review of memory compaction I see that it already adds its own recount and unifies it too with the ksm_refcount. So it's worth stop calling it ksm_refcount and to remove the #ifdef (which memory compaction didn't remove but added an defined(CONFIG_KSM) || defined(CONFIG_MIGRATION)).
If you do this change we can have your change applied first, and then Mel can adapt memory compaction to it sharing the same unconditional compiled-in refcount.
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