[webkit-changes] [WebKit/WebKit] c8e9c0: Add support for full GC during opportunistically s...

[Wenson Hsieh]

  Branch: refs/heads/main
  Home:   https://github.com/WebKit/WebKit
  Commit: c8e9c0c0c8605b26d8225c67cd5afdf5598feb37
      https://github.com/WebKit/WebKit/commit/c8e9c0c0c8605b26d8225c67cd5afdf5598feb37
  Author: Wenson Hsieh <wenson_hsieh at apple.com>
  Date:   2023-09-15 (Fri, 15 Sep 2023)

  Changed paths:
    M Source/JavaScriptCore/heap/Heap.cpp
    M Source/JavaScriptCore/heap/Heap.h
    M Source/JavaScriptCore/runtime/VM.cpp
    M Source/WebCore/loader/SubframeLoader.cpp
    M Source/WebCore/page/Page.cpp
    M Source/WebCore/page/Page.h

  Log Message:
  -----------
  Add support for full GC during opportunistically scheduled tasks
https://bugs.webkit.org/show_bug.cgi?id=261491
rdar://113241499

Reviewed by Yusuke Suzuki.

Add support for triggering full GC during opportunistically scheduled tasks. This is similar to the
previous work done for eden GC in 267893 at main, only (generally) more restrictive:

1.  We use `m_totalBytesVisited`, `m_totalBytesVisitedAfterLastFullCollect`, and the duration of the
    last GC to (more accurately) estimate the cost of a full GC.

2.  We only attempt full GC here if `m_shouldDoOpportunisticFullCollection` is `true`; this flag is
    only set when changing the location of a subframe, which has previously finished loading content
    (see below for more details).

3.  Instead of a 10 ms hysteresis, we add an extended hysteresis such that we don't trigger
    opportunistic full GC if we've already finished a full GC in the last 30 ms.

* Source/JavaScriptCore/heap/Heap.cpp:
(JSC::Heap::updateObjectCounts):

Keep track of `m_totalBytesVisitedAfterLastFullCollect` here (that is — `m_totalBytesVisited`, but
for the last full GC).

(JSC::Heap::runEndPhase):

Update the new `m_lastFullGCEndTime` alongside `m_lastGCEndTime`, only if we're ending a full GC
cycle.

(JSC::Heap::willStartCollection):
(JSC::Heap::updateAllocationLimits):
(JSC::Heap::scheduleOpportunisticFullCollectionIfNeeded):

Add a hook into `JSC::Heap` to set the `m_shouldDoOpportunisticFullCollection` flag only in the case
where `shouldDoFullCollection()` is set. See call site below in `Page`.

* Source/JavaScriptCore/heap/Heap.h:
* Source/JavaScriptCore/runtime/VM.cpp:
(JSC::VM::performOpportunisticallyScheduledTasks):

Add logic to conditionally trigger full opportunistic GC. We also refactor this to use an inline
lambda block, so that we can make the code a bit easier to follow with early returns. This also
allows us to fall back to an eden GC in the case where we don't have enough time budget for a full
GC cycle.

* Source/WebCore/loader/SubframeLoader.cpp:
(WebCore::FrameLoader::SubframeLoader::loadOrRedirectSubframe):

Add a hook to call into `Page` when changing the location of a subframe, only if that subframe had
previously finished loading prior content.

* Source/WebCore/page/Page.cpp:
(WebCore::Page::willChangeLocationInCompletelyLoadedSubframe):
* Source/WebCore/page/Page.h:

Canonical link: https://commits.webkit.org/268039@main