[SCM] GNU Mach branch, rbraun/vm_cache_policy, created. v1.4-4-g98d64d1

[Richard Braun]

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The branch, rbraun/vm_cache_policy has been created
        at  98d64d1a78172b1efc26cac36a367eec8496926f (commit)

- Log -----------------------------------------------------------------
commit 98d64d1a78172b1efc26cac36a367eec8496926f
Author: Richard Braun <address@hidden>
Date:   Wed Oct 9 11:51:54 2013 +0200

    VM cache policy change
    
    This patch lets the kernel unconditionnally cache non empty unreferenced
    objects instead of using a fixed arbitrary limit. As the pageout daemon
    evicts pages, it collects cached objects that have become empty. The
    effective result is a graceful adjustment of the number of objects
    related to memory management (virtual memory objects, their associated
    ports, and potentially objects maintained in the external memory
    managers). Physical memory can now be almost entirely filled up with
    cached pages. In addition, these cached pages are not automatically
    deactivated as objects can quickly be referenced again.
    
    There are problems with this patch however. The first is that, on
    machines with a large amount of physical memory (above 1 GiB but it also
    depends on usage patterns), scalability issues are exposed. For example,
    file systems which don't throttle their writeback requests can create
    thread storms, strongly reducing system responsiveness. Other issues
    such as linear scans of memory objects also add visible CPU overhead.
    
    The second is that, as most memory is used, it increases the chances of
    swapping deadlocks. Applications that map large objects and quickly
    cause lots of page faults can still easily bring the system to its
    knees.

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