Save a call to pmap_remove() if entry cannot have any pages mapped.
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Authored by kib on Jul 5 2018, 7:08 PM.

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alc
markj

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rS336045: Save a call to pmap_remove() if entry cannot have any pages mapped.
rS336030: Save a call to pmap_remove() if entry cannot have any pages mapped.
rS336029: Style: no need for braces around single-line then clause.

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rS FreeBSD src repository - subversion

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kib created this revision.Jul 5 2018, 7:08 PM

Herald added a subscriber: imp. · View Herald TranscriptJul 5 2018, 7:08 PM

Harbormaster completed remote builds in B17872: Diff 44933.Jul 5 2018, 7:08 PM

FYI, I just did a "buildworld" where I counted the number of times that the pmap_remove() could be avoided ("debug.counter1") and the number of times that the pmap_remove() was needed ("debug.counter2"). The results are:

debug.counter1: 2044614
debug.counter2: 8117202

I'm actually surprised by how large debug.counter1 is.

This revision is now accepted and ready to land.Jul 5 2018, 10:47 PM

In D16148#342543, @alc wrote:
FYI, I just did a "buildworld" where I counted the number of times that the pmap_remove() could be avoided ("debug.counter1") and the number of times that the pmap_remove() was needed ("debug.counter2"). The results are:
debug.counter1: 2044614
debug.counter2: 8117202
I'm actually surprised by how large debug.counter1 is.

I added a dtrace probe before the pmap_remove() call so that I could dump the vm_map_entry. Most (~80%) of the no-op calls seem to be a result of the use of MAP_FIXED in rtld: as it maps segments of shared objects, vm_map_fixed() deletes subranges of the guard mapping.

markj accepted this revision.Jul 6 2018, 1:59 AM

Closed by commit rS336029: Style: no need for braces around single-line then clause. (authored by kib). · Explain WhyJul 6 2018, 12:37 PM

This revision was automatically updated to reflect the committed changes.

kib reopened this revision.Jul 6 2018, 12:38 PM

This revision was not accepted when it landed; it landed in state Needs Review.Jul 6 2018, 12:45 PM

Closed by commit rS336030: Save a call to pmap_remove() if entry cannot have any pages mapped. (authored by kib). · Explain Why

This revision was automatically updated to reflect the committed changes.