Re: [PATCH 2.5.43-mm2] New shared page table patch

[ebiederm@xmission.com (Eric W. Biederman)]

Dave McCracken <dmccr@us.ibm.com> writes:

> This patch isn't primarily a performance patch.  It does help for some
> things, notably the fork/exec/exit cases mentioned above.  But its primary
> goal is to reduce the amount of memory wasted in page tables mapping the
> same pages into multiple processes.  We have seen an application that
> consumed on the order of 10 GB of page tables to map a single shared memory
> chunk across hundreds of processes.  Shared page tables would eliminate
> this overhead.

Have you considered putting a fixed upper bound on the number of pages
tables a page can be mapped into?  This would result in the same amount
of memory reduction, with what should be very little complexity.

I admit there would be a few more demand paging hits, but they should be
controllable.  And I suspect their performance impact would be lost
in the noise.

Eric
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