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List:       freebsd-mips
Subject:    [RFC] TLB-based reference bit emulation (patches)
From:       Stacey Son <sson () FreeBSD ! org>
Date:       2014-02-24 21:50:41
Message-ID: AB889344-ABEF-4D4F-86FD-A3D0EAA6E095 () FreeBSD ! org
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Hi all:

Below are some links to patches that adds TLB-based reference bit emulation for MIPS \
hardware with 64-bit physical addressing.  This is similar to what is described in \
the paper "Page Replacement and Reference Bit Emulation in Mach" by Richard P. \
Draves.  However, unlike the Mach implementation the reference bit (or actually a \
*not* referenced bit) is in the page table entry (PTE) and not in separate array \
somewhere else in memory.  The reference bit is set (or actually cleared) in the TLB \
miss handler. With a PTE reference bit it is now possible to have a complete \
implementation of pmap_ts_referenced() and to correctly determine if the address is \
"MINCORE_REFERENCED" in pmap_mincore().

The first patch actually adds free lists (and pmap_free_zero_pages() and \
pmap_add_delayed_free_list()).   The second patch adds the (not) reference bit \
changes for exception.S and pmap.c.  Currently this change only applies to MIPS with \
64 bit physical addresses because there is no room for another PTE bit with MIPS32.  \
Does anyone have any ideas for the MIPS32 case other than the way it was done in \
Mach?

http://people.freebsd.org/~sson/mips/superpages/pmap_freelist_1.diff
http://people.freebsd.org/~sson/mips/superpages/pmap_reference_bit_2.diff

Next up is pmap_copy() and superpages.

Best Regards,

-stacey.
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