Messages in this thread | | | Subject | Re: [PATCH 00/11] V4: rwsem changes + down_read_critical() proposal | From | Peter Zijlstra <> | Date | Tue, 25 May 2010 11:27:55 +0200 |
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On Tue, 2010-05-25 at 02:12 -0700, Michel Lespinasse wrote: > On Tue, May 25, 2010 at 1:47 AM, Peter Zijlstra <peterz@infradead.org> 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 be __GFP_HARDWALL|__GFP_HIGHMEM|__GFP_MOVABLE__GFP_NOWARN or (GFP_HUGHUSER_MOVABLE & ~(__GFP_WAIT|__GFP_IO|__GFP_FS))|__GFP_NOWARN
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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