James Bottomley wrote:
On Tue, 2006-05-30 at 18:57 -0700, H. Peter Anvin wrote:
Does any of the i386 subarchitectures actually care about the Accessed and Dirty bits in
the bootup pagetables (the ones that start at pg0, used before the mm is initialized?) If
not, I'd like to speed up booting by setting those bits at initialization time.
Depends what you mean by "care". I do hijack pg0 in
voyager_memory_detect() to access the clickmap for ascertaining the
memory layout, but I don't use the accessed or dirty bits.
Okay...
Leaving the A and D bits clear means the CPU has to trap to microcode to
set those bits before it is allowed to load the entry into the TLB.
Furthermore, and this is the real killer on some CPUs, it is not allowed
to load those entries speculatively.
As far as I can tell, this is completely pointless for pg0.
(And no, the Voyager code wouldn't be affected.)
-hpa
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