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SubjectRe: [PATCH 00/11] V4: rwsem changes + down_read_critical() proposal
On Tue, 2010-05-25 at 02:12 -0700, Michel Lespinasse wrote:
> On Tue, May 25, 2010 at 1:47 AM, Peter Zijlstra <> wrote:
> > So what happened to those patches that dropped mmap_sem during I/O?
> Yes, we do have patches trying to release the mmap_sem when a page
> fault for a file backed VMA blocks on accessing the corresponding
> file. We have not given up on these, and we intend to try submitting
> them again. However, these patches do *not* address the case of a page
> fault blocking while trying to get a free page (i.e. when you get
> under high memory pressure).

But I guess they could, right? Simply make the allocation under mmap_sem
and drop the mmap_sem when that fails.

> > I really don't like people tinkering with the lock implementations like
> > this. Nor do I like the naming, stats are in no way _critical_.
> Critical here refers to the fact that you're not allowed to block
> while holding the unfairly acquired rwsem.

We usually call that atomic, your 0/n patch didn't explain any of that.

Also, do you really think doing something like:

* Check the vma index is within the range and do
* sequential scan until m_index.
vma = NULL;
if ((unsigned long)l < mm->map_count) {
vma = mm->mmap;
while (l-- && vma)
vma = vma->vm_next;
goto out;
with preemption disabled is a _good_ thing?

People were talking about raising our vma limit of 64k...

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