Alternatively if you know your memory usage pattern an arena allocator could work faster here for you think zero on delete. The pages have to come from the operating system. Writing a custom allocator is not going to solve this problem. Linux supports page allocation without erasing previous contents as a kernel config somewhere. It would be interesting to compare allocation speed with and without it. To get hugepages you have go jump through more hoops, e.
You can use mmap directly or one of the aligned allocators. Better, you can check to see if you got huge pages: I wrote page-info to do that, integrating it is fairly easy you can find integrations in some of our shared projects, including how to jump through the aforementioned hoops. Note that it only works on Linux. Your email address will not be published. The comment form expects plain text. If you need to format your text, you can use HTML elements such strong, blockquote, cite, code and em.
Save my name, email, and website in this browser for the next time I comment. You may subscribe to this blog by email. Skip to content My home page My papers My software. Footnotes : Several readers have asked why I am ignoring C functions like calloc , malloc and mmap. Using malloc creates a smaller binary and your program will load from disk faster.
Using malloc and free judiciously can keep peak memory demand low and reduce system paging. Paging misnamed swapping in Linux is horribly slow. Using malloc and free cost cpu time and used stupidly can significantly slow down a program. Malloc is a kernel call and the kernel has to scan its free memory queue and move some free memory to your program's exclusive use. Non-dynamic allocation does not involve the kernel at all.
Originally Posted by CoderMan. Originally Posted by jailbait. Last edited by johnsfine; at PM. At most 60 structs? That's 15KB. If this much memory is a problem I guess you're designing your program to run in an embedded system, right? If it's an embedded system with so little memory then I imagine there won't be any operating system and your situation would be different. If it is a PC then you don't have to worry, your process will already have much more then 15KB allocated when it starts running.
The code will be different and one might be faster than the other, and it seems more likely that this performance difference would matter rather than the malloc overhead mattering. Last edited by irey; at AM. Last edited by ErV; at AM. Thread Tools. Every call to malloc can fail, and you should test that. You may want to read Advanced Linux Programming and some more general material about operating systems, e. Operating Systems: three easy pieces. Notice that reference counting can be viewed as a form of GC a poor one, which does not handle well reference cycles or cyclic graphs There are some caveats when using Boehm's GC.
You might consider other GC schemes or libraries Use strace 1 to find out the system calls done by your or some other program. First, malloc and free work together, so testing malloc by itself is misleading. Second, no matter how good they are, they can easily be the dominant cost in any application, and the best solution to that is to call them less. Calling them less is almost always the winning way to fix programs that are malloc -limited.
One common way to do this is to recycle used objects. When you're done with a block, rather than free -ing it, you chain it on a used-block stack and re-use it the next time you need one. And yes, if you omit thread-support from your allocator, you can achieve a significant performance gain. I have seen a similar speedup with my own non-thread-safe allocator. However, a standard implementation needs to be thread-safe. It needs to account for all of the following:.
Different threads use malloc and free concurrently. That means, that the implementation cannot access global state without internal synchronization. Since locks are really expensive, typical malloc implementations try to avoid using global state as much as possible by using thread-local storage for almost all requests. A thread that allocates a pointer is not necessarily the thread that frees it.
This has to be taken care of. A thread may constantly allocate memory and pass it to another thread to free it. This makes handling of the last point much more difficult, because it means that free blocks may accumulate within any thread-local storage. This forces the malloc implementation to provide means for the threads to exchange free blocks, and likely requires grabbing of locks from time to time.
If you don't care about threads, all these points are no issues at all, so a non-thread-safe allocator does not have to pay for their handling with performance. But, as I said, a standard implementation cannot ignore these issues, and consequently has to pay for their handling. If you compare a real malloc implementation with a school project, consider that a real malloc has to manage allocations, reallocations and freeing memory of hugely different sizes, working correctly if allocations happen on different threads simultaneously, and reallocation and freeing memory happen on different threads.
You also want to be sure that any attempt to free memory that wasn't allocated with malloc gets caught. However, you will need to introduce some kind of synchronization, since the memory for the objects is created and destroyed in two separate threads. One solution to the synchronization problem is to cache memory chunks both on the allocate end and deallocate end. This decreases the need for synchronization. Take a look at the following source code:.
This solution works only with two threads, one thread that exclusively allocates and the other thread exclusively deallocates objects. Small values make the allocator useless, as most of the time it is working with the system allocator instead of the cached chunk lists.
A large value makes the program consume more memory. On line 4 we allocate memory for the object, but only on line 5 we call the constructor. The piece of the memory on which the object is created is given in parenthesis, after the keyword new. On line 8 we explicitly call the constructor. The object is destroyed, but the memory is not released back. We release the memory back to the pool on line 9. Alternatively, you can override operator new and operator delete , like this:.
This will make every object created using new and destroyed using delete allocated using memory from the memory pool.
Here is the source code of a naive implementation:. What we could do, is that we could preallocate two integers as a part of the class and thus completely avoid calls to the system allocator. The code now looks like this:.
The downside of this approach is the increase in class size. On 64 bit system, the original class was 24 bytes in size, the new class is 32 bytes in size. Luckily, we can have both small size and small buffer optimizations in the same package with a trick. We can use C unions to overlay the data for the preallocated case and for the heap-allocated case.
Here is the source code:. This approach is used in several places. The techniques mentioned up to this point are domain-specific. In this section we talk about another way to speed up your program: by using a better system allocator.
On Linux, there are several open-source allocators that try to solve the problem of efficient allocation and deallocation, but no allocator, as far as I know, can solve all the problems completely. When you are picking a system allocator for your system, there are four properties that each allocator compromises on:. Its allocator is called GNU allocator and it is based on ptmalloc.
Apart from it, there are several other open-source allocators commonly used on Linux : tcmalloc by Google , jemalloc by Facebook , mimalloc by Microsoft , hoard allocator , ptmalloc and dlmalloc. GNU allocator is not among the most efficient allocators. However it does have one advantage, the worst-case runtime and memory usage will not be too bad. But the worst case happens rarely and it is definitely worth investigating if we can do better.
Other allocators claim to be better in speed, memory usage or cache locality. Still, when you are picking the right one for you, you should consider:. Well, this time there will not be any experiments. The reason is simple: real-world programs differ too much from one another. An allocator that performs well under one load might have different behavior under another load. The author has compared several allocators on a test load that tries to simulate a real-world load.
We will not repeat the results of his analysis here, but his conclusion matches ours: allocators are similar to one another and testing your particular application is more important than relying on synthetic benchmarks. You can use this trick to quickly check if the allocator fits your needs:. All the allocators can be fine-tuned to run better on a particular system , but the default configuration should be enough for most use cases.
Fine-tuning can be done at compile-time or run-time, through environment variables, configuration files or compilation options.
Normally the allocators provide implementations for malloc and free and will replace the functions with the same name provided by Standard C library. This means that every dynamic allocation your program makes goes through the new allocator. However, it is possible to keep default malloc and free implementations together with custom implementations provided by your chosen allocator. Allocators can provide prefixed versions of malloc and free for this purpose. For example, jemalloc allows you to provide a custom prefix for malloc and free.
We presented several techniques on how to make your program allocate memory faster.
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