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Subject'disposable' dirty pages [was: Out Of Memory in v. 2.1]

On Tue, 6 Oct 1998, Stephen C. Tweedie wrote:

> If you let user processes allocate all memory then _something_ has got
> to die. There's no way round that. You are not suggesting any
> solution to that fundamental problem.

while i have no fundamental solution to this fundamentally unsolvable
problem, maybe there is something we could do to get applications
cooperate better with the VM system. There is the example of AIX, where
they have a signal (SIGNOMEM?) to nonfatally alert processes to free up
memory. This approach is quite kludgy and an application never knows as
much as the VM system about the state of memory usage.

But what about a new (?) approach, 'disposable mappings'. This would be a
per-vma property, just like 'read-only' and 'grows-down', 'disposable'
defines new behavior: the kernel is free to drop even dirty pages too from
such a vma. libc could be one of the early users: the malloc cache has
potentially many dirty pages which have no information content. Whenever a
process accesses a 'disposed' vma, it gets a page-fault, and libc has to
fix things up by newly allocating and mapping new memory. Another user
could be X by marking it's internal, recreatable caches (which are dirty)
as disposable.

-- mingo


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