Opportunistically update the page's dirty field in pmap_ts_referenced().
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Authored by alc on Aug 31 2016, 4:23 PM.

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kib
markj

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rS305213: As an optimization to the machine-independent layer, change the machine-

Summary

This change has us opportunistically updating the page's dirty field in pmap_ts_referenced(). I think that the comments explain the benefits.

This won't eliminate pmap_is_modified() calls when the page is not mapped for write access, but those cases are handled efficiently by pmap_is_modified() using the PGA_WRITEABLE flag. Only writeable pages that have not been written to will bear the full cost of pmap_is_modified().

This is a work in progress. I've only written the amd64 implementation as a demonstration.

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alc updated this revision to Diff 19875.Aug 31 2016, 4:23 PM

alc retitled this revision from to Opportunistically update the page's dirty field in pmap_ts_referenced()..

alc updated this object.

alc edited the test plan for this revision. (Show Details)

alc added reviewers: kib, markj.

Here is some data from the debug counters.

debug.counter_yes: 59075
debug.counter_no: 246172

These values come after 3 and a fraction iterations of a parallel "buildworld" on a machine configured with 3GB memory.

markj accepted this revision.Aug 31 2016, 6:16 PM

markj edited edge metadata.

markj added inline comments.

amd64/amd64/pmap.c
5901	Is there a reason these assignments are in the loop bodies rather than being lifted to the top of the function?

This revision is now accepted and ready to land.Aug 31 2016, 6:16 PM

alc marked an inline comment as done.Aug 31 2016, 6:25 PM

alc added inline comments.

amd64/amd64/pmap.c
5901	Yes, they could change from one pmap to the next. Specifically, on Intel processors, we could have both EPT and regular format page tables.

kib accepted this revision.Aug 31 2016, 7:02 PM

kib edited edge metadata.

Since this is an optimization, I don't need to change the pmap implementations all at once, so I will likely commit this change in a few hours.

Closed by commit rS305213: As an optimization to the machine-independent layer, change the machine- (authored by alc). · Explain WhySep 1 2016, 3:58 PM

This revision was automatically updated to reflect the committed changes.

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amd64/

pmap.c

24 lines

vm/

vm_pageout.c

10 lines

Diff 19875

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amd64/amd64/pmap.c