lkml.org 
[lkml]   [2008]   [May]   [9]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH 08 of 11] anon-vma-rwsem
From
Date
On Thu, 2008-05-08 at 09:11 -0700, Linus Torvalds wrote:
>
> On Thu, 8 May 2008, Linus Torvalds wrote:
> >
> > Also, we'd need to make it
> >
> > unsigned short flag:1;
> >
> > _and_ change spinlock_types.h to make the spinlock size actually match the
> > required size (right now we make it an "unsigned int slock" even when we
> > actually only use 16 bits).
>
> Btw, this is an issue only on 32-bit x86, because on 64-bit one we already
> have the padding due to the alignment of the 64-bit pointers in the
> list_head (so there's already empty space there).
>
> On 32-bit, the alignment of list-head is obviously just 32 bits, so right
> now the structure is "perfectly packed" and doesn't have any empty space.
> But that's just because the spinlock is unnecessarily big.
>
> (Of course, if anybody really uses NR_CPUS >= 256 on 32-bit x86, then the
> structure really will grow. That's a very odd configuration, though, and
> not one I feel we really need to care about).

Another possibility, would something like this work?


/*
* null out the begin function, no new begin calls can be made
*/
rcu_assing_pointer(my_notifier.invalidate_start_begin, NULL);

/*
* lock/unlock all rmap locks in any order - this ensures that any
* pending start() will have its end() function called.
*/
mm_barrier(mm);

/*
* now that no new start() call can be made and all start()/end() pairs
* are complete we can remove the notifier.
*/
mmu_notifier_remove(mm, my_notifier);


This requires a mmu_notifier instance per attached mm and that
__mmu_notifier_invalidate_range_start() uses rcu_dereference() to obtain
the function.

But I think its enough to ensure that:

for each start an end will be called

It can however happen that end is called without start - but we could
handle that I think.





\
 
 \ /
  Last update: 2008-05-09 20:39    [W:0.196 / U:0.256 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site