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0033138: [Foundation Classes] - NCollection_IncAllocator- Decrease the default block size

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Set default memory block size for IncAllocator to 12KB to make sure the Low Fragmentation Heap is used for memory allocations on Windows platform.
This commit is contained in:
Eugeny Maltchikov 2022-09-12 11:00:49 +03:00 committed by smoskvin
parent 259b930379
commit 9218d04b9a
2 changed files with 15 additions and 3 deletions
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2
dox/user_guides/foundation_classes/foundation_classes.md
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@ -1331,7 +1331,7 @@ Therefore if the user of *NCollection* does not specify any allocator as a param
Nevertheless, it is possible to define a custom *Allocator* type to manage the memory in the most optimal or convenient way for this algorithm.
As one possible choice, the class *NCollection_IncAllocator* is included.
Unlike *NCollection_BaseAllocator*, the memory is allocated in big blocks (about 20kB) and the allocator keeps track of the amount of occupied memory.
Unlike *NCollection_BaseAllocator*, the memory is allocated in big blocks (about 12kB) and the allocator keeps track of the amount of occupied memory.
The method *Allocate* just increments the pointer to non-occupied memory and returns its previous value.
Memory is only released in the destructor of *NCollection_IncAllocator*, the method *Free* is empty.
If used properly, this Allocator can greatly improve the performance of specific algorithms.

16
src/NCollection/NCollection_IncAllocator.hxx
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@ -33,7 +33,12 @@ class Standard_Mutex;
* type "aligned_t". To modify the size of memory blocks requested from the
* OS, use the parameter of the constructor (measured in bytes); if this
* parameter is smaller than 25 bytes on 32bit or 49 bytes on 64bit, the
* block size will be the default 24 kbytes
* block size will be the default 12 kbytes.
*
* It is not recommended to use memory blocks larger than 16KB on Windows
* platform for the repeated operations because Low Fragmentation Heap is
* not going to be used for these allocations which may lead to memory
* fragmentation and the general performance slow down.
*
* Note that this allocator is most suitable for single-threaded algorithms
* (consider creating dedicated allocators per working thread),
@ -50,6 +55,12 @@ class NCollection_IncAllocator : public NCollection_BaseAllocator
//! Constructor.
//! Note that this constructor does NOT setup mutex for using allocator concurrently from different threads,
//! see SetThreadSafe() method.
//!
//! The default size of the memory blocks is 12KB.
//! It is not recommended to use memory blocks larger than 16KB on Windows
//! platform for the repeated operations (and thus multiple allocations)
//! because Low Fragmentation Heap is not going to be used for these allocations,
//! leading to memory fragmentation and eventual performance slow down.
Standard_EXPORT NCollection_IncAllocator (size_t theBlockSize = DefaultBlockSize);
//! Setup mutex for thread-safe allocations.
@ -83,7 +94,8 @@ class NCollection_IncAllocator : public NCollection_BaseAllocator
Standard_EXPORT void Reset (const Standard_Boolean
doReleaseMem=Standard_True);
static const size_t DefaultBlockSize = 24600;
//! Default size for the memory blocks - 12KB
static const size_t DefaultBlockSize = 12300;
protected:
struct IBlock;