Messages in this thread Patch in this message | | | Date | Mon, 30 Sep 2013 13:44:06 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH, v2] anon_vmas: Convert the rwsem to an rwlock_t |
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On Sat, Sep 28, 2013 at 09:52:07PM +0200, Ingo Molnar wrote: > Index: tip/mm/mmap.c > =================================================================== > --- tip.orig/mm/mmap.c > +++ tip/mm/mmap.c > @@ -2955,15 +2955,15 @@ static void vm_lock_anon_vma(struct mm_s > * The LSB of head.next can't change from under us > * because we hold the mm_all_locks_mutex. > */ > - down_write_nest_lock(&anon_vma->root->rwsem, &mm->mmap_sem); > + write_lock(&anon_vma->root->rwlock);
Tssk, you should know better...
But yes; this is the most horrid site; however I think it was mostly file based VMAs that caused the immense amount of locks taken since this is only done 'very' early on in the life of KVM.
I can't remember how early; I hope almost instantly and certainly before spawning all the various vcpu threads as that would create all the thread stacks which are anon and would indeed blow up the non-preempt time here.
So if we keep i_mmap_mutex -- and I hope we do; that unmap_mutex horror wasn't pretty at all -- see commit 97a894136 . The below shouldn't be too bad I think/hope.
--- --- a/include/linux/rwlock.h +++ b/include/linux/rwlock.h @@ -64,6 +64,19 @@ do { \ #define write_lock(lock) _raw_write_lock(lock) #define read_lock(lock) _raw_read_lock(lock) +#ifdef CONFIG_DEBUG_LOCK_ALLOC +# define write_lock_nest_lock(lock, nest_lock) \ +do { \ + typecheck(struct lockdep_map *, &(nest_lock)->dep_map); \ + preempt_disable(); \ + lock_acquire_exclusive(&lock->dep_map, 0, 0, \ + &(nest_lock)->dep_map, _RET_IP_); \ + LOCK_CONTENDED(lock, do_raw_write_trylock, do_raw_write_lock); \ +} while (0) +#else +# define write_lock_nest_lock(lock, nest_lock) write_lock(lock) +#endif + #if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK) #define read_lock_irqsave(lock, flags) \ --- a/mm/mmap.c +++ b/mm/mmap.c @@ -2955,7 +2955,7 @@ static void vm_lock_anon_vma(struct mm_s * The LSB of head.next can't change from under us * because we hold the mm_all_locks_mutex. */ - write_lock(&anon_vma->root->rwlock); + write_lock_nest_lock(&anon_vma->root->rwlock); /* * We can safely modify head.next after taking the * anon_vma->root->rwlock. If some other vma in this mm shares
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