tree 41ab55a471f729e677a2eaf3a5be645934beb369
parent 152df6ff719ae29e87ba8393f6c92bcc0163446f
author Adrian Danis <adanis@google.com> 1603849325 +0000
committer CQ Bot <commit-bot@chromium.org> 1603849325 +0000

[kernel][vm] Remove hidden parents from VmObjectPaged

This removes the notion of hidden parents from VmObjectPaged and in
the process places control of the VmCowPages hierarchy manipulation in
the VmCowPages code, instead of being done from the VmObjectPaged.

Aside from the removal of the redundant VmObjectPaged hidden parents
this also performs an additional optimization of making the parent_
reference in VmObjectPaged a raw reference and not a RefPtr. This
can be done since now that the copy-on-write pages are held in
VmCowPages there is no reason to hold the VmObjectPaged around after
any other references, such as user handles and mappings, have gone
away. Not holding the parent via a refptr also ensures we can not have
any chained deletions and so the deferred deletion mechanism is only
needed now by VmCowPages.

Change-Id: I710eab49b583542f2a773f130319d5b4a8dfc7e8
Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/437347
Testability-Review: Adrian Danis <adanis@google.com>
Testability-Review: Rasha Eqbal <rashaeqbal@google.com>
Commit-Queue: Adrian Danis <adanis@google.com>
Reviewed-by: Rasha Eqbal <rashaeqbal@google.com>