pmap mmu optimization turned off on master (a week ago)

Matthew Dillon dillon at
Mon Dec 10 09:08:35 PST 2012

    We've turned off the machdep.pmap_mmu_optimize feature by default
    on master.  Note that it was never enabled (by default) for the 3.2
    release branch.

    Currently there are two issues with the feature that need to be fixed.
    These issues have cropped up in wider testing over the last month.
    At the moment we do NOT recommend that anyone use this feature.

    (1) There is a corruption issue somewhere which has yet to be found,
        which shows up in rtorrent and apache.

    (2) The pmap backing the VM objects which is used to provide the basis
	for page table sharing might not be getting deallocated properly,
	and is also not being garbage collected, and this *could* be
	responsible for reports of bloated page 'wire' counts and lost
	memory on machines over time.

    These issues basically just require some bug work, I don't expect to
    have to do any major reworking of the code so the feature WILL
    definitely become standard at some point in 2013.   But for now I
    recommend that it not be used.

					Matthew Dillon 
					<dillon at>

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