Messages in this thread | | | Date | Fri, 29 Feb 2008 01:40:01 +0100 | From | Andrea Arcangeli <> | Subject | Re: [PATCH] mmu notifiers #v7 |
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On Thu, Feb 28, 2008 at 03:05:30PM -0800, Christoph Lameter wrote: > Still think that the lock here is not of too much use and can be easily > replaced by mmap_sem.
I can use the mmap_sem.
> > +#define mmu_notifier(function, mm, args...) \ > > + do { \ > > + struct mmu_notifier *__mn; \ > > + struct hlist_node *__n; \ > > + \ > > + if (unlikely(!hlist_empty(&(mm)->mmu_notifier.head))) { \ > > + rcu_read_lock(); \ > > + hlist_for_each_entry_rcu(__mn, __n, \ > > + &(mm)->mmu_notifier.head, \ > > + hlist) \ > > + if (__mn->ops->function) \ > > + __mn->ops->function(__mn, \ > > + mm, \ > > + args); \ > > + rcu_read_unlock(); \ > > + } \ > > + } while (0) > > Andrew recomended local variables for parameters used multile times. This > means the mm parameter here.
I don't exactly see what "buggy macro" meant? I already use parenthesis as needed to avoid the need of local variables to be safe. Not really sure what's buggy, sorry!
> Note also Andrew's comments on the use of 0x00ff...
I thought I tried the (void) but it didn't work and your solution worked, but perhaps I did something wrong, I'll try again with (void) nevertheless.
> > +/* > > + * No synchronization. This function can only be called when only a single > > + * process remains that performs teardown. > > + */ > > +void mmu_notifier_release(struct mm_struct *mm) > > +{ > > + struct mmu_notifier *mn; > > + struct hlist_node *n, *tmp; > > + > > + if (unlikely(!hlist_empty(&mm->mmu_notifier.head))) { > > + hlist_for_each_entry_safe(mn, n, tmp, > > + &mm->mmu_notifier.head, hlist) { > > + hlist_del(&mn->hlist); > > + if (mn->ops->release) > > + mn->ops->release(mn, mm); > > + } > > + } > > +} > > One could avoid a hlist_for_each_entry_safe here by simply always deleting > the first object.
Agreed, the current construct come from the fact we previously didn't assume nobody could ever call mmu_notifier_unregister by the time mm_users is 0.
> Also re the _notify variants: The binding to pte_clear_flush_young etc > will become a problem for notifiers that want to sleep because > pte_clear_flush is usually called with the pte lock held. See f.e. > try_to_unmap_one, page_mkclean_one etc.
Calling __free_page out of the PT lock is much bigger change. do_wp_page will require changes anyway when the sleepable notifiers are merged.
> It would be better if the notifier calls could be moved outside of the > pte lock.
The point is that it can't make a difference right now, and my objective was to avoid unnecessary source code duplication (later it will be necessary, right now it isn't). By the time you rework do_wp_page, removing _notify will be a very minor detail compared to the rest of the changes to do_wp_page IMHO. Expanding it now won't provide a real advantage later.
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