Large graphical Qt applications heavily rely on heap allocations.
Jemalloc is a general-purpose malloc(3) implementation designed to
reduce heap fragmentation and improve scalability. It also provides
extensive tuning options.
Add a -jemalloc configure option, disabled by default. When enabled, Qt
and user code link to jemalloc, overriding the system's default
malloc().
Add cooperation with jemalloc for some Qt key classes: QArrayData (used
by QByteArray, QString and QList<T>), QBindingStoragePrivate,
QDataBuffer (used by the Qt Quick renderer), QDistanceFieldData,
QImageData, QObjectPrivate::TaggedSignalVector, QVarLengthArray.
This cooperation relies on two jemalloc-specific optimizations:
1. Efficient allocation via fittedMalloc():
Determine the actual allocation size using nallocx(), then adjust the
container’s capacity to match. This minimizes future reallocations.
Note: we round allocSize to a multiple of sizeof(T) to ensure that
we can later recompute the exact allocation size during deallocation.
2. Optimized deallocation via sizedFree():
Use sdallocx(), which is faster than free when the allocation size
is known, as it avoids internal size lookups.
Adapt the QVarLengthArray auto tests on capacity.
Non-standard functions docs are at https://jemalloc.net/jemalloc.3.html
[ChangeLog][QtCore] Added optional support for the jemalloc allocator,
and optimized memory allocations and deallocations in core Qt classes to
cooperate with it.
Change-Id: I6166e64e66876dee22662d3f3ea3e42a6647cfeb
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
