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SubjectRe: Ideas for memory management hackers (2)
On 16 Nov 1997, Hans-Christoph Rohland wrote:
> (I discussed some of these items with David Miller at Linux Kongress,
> Germany. Dave you remember?)
> I think the virtual memory support in linux has the following
> weaknesses irt. applications which use loads of virtual memory in
> parallel processes:
> - Support for shared pages:
> - No aging (?)
fixed by my patch (vhand)

> - VM areas are limited to 128MB. This leads to many swap-files. (I am
> not quite shure about further limitation. Does it mean that bigger
> mmaps are not possible? The swapfile limitation is definitely in the
> kernel.)

Are they???

> 1) Good support for swapping of shared pages

Aging is step 1, efficiency will have to be looked into...

> 4) implementation of the 'madvise' call, especially the MADV_DONTNEED
> parameter.

This could be done by a simple syscall whereby a process sets
the age of a specified (own) page to 0.

> The need for MADV_DONTNEED is a similar problem: no memory manager can
> know that I really don't need a part of memory any more. It will
> always try to save the memory in backing store.
> But especially transactional programs process some memory and when the
> transaction finishes there is no need to get this content again. It
> will be overwritten by the next transaction. So the program can
> advise the OS to simply discard the page instead of saving the page to
> the swapfile. This can increase the system performance a lot under low
> physical memory.

Ahh, I get it. Now, how should we implement this one?


PLEASE, test my vhand patch and send comments/flames/code improvements
to me...
Send Linux memory-management wishes to me: I'm currently looking
for something to hack...

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