blocks|key|633250|text|您可以做的一件事是让分配器分配一个内存池，然后为来自than的请求提供服务(如果内存池用完，则分配一个更大的内存池)。我不确定这是不是他们在做的事情。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|633251|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

One thing you can do is have your allocator allocate a pool of memory, then service requests from than (and allocate a bigger pool if it runs out). I'm not sure if that's what they're doing though.

blocks|key|1666519|text|参见How+do+games+like+GTA+IV+not+fragment+the+heap?。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1666520|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/questions/4687643/how-do-games-like-gta-iv-not-fragment-the-heap^0|2|1B|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@$A|M|B|N|1|O]]|C|$]]|$1|D|3|-4|5|6|7|P|8|@]|9|@]|C|$]]]|E|$F|$5|G|H|I|C|$J|K]]]]

See <a href="https://stackoverflow.com/questions/4687643/how-do-games-like-gta-iv-not-fragment-the-heap">How do games like GTA IV not fragment the heap?</a>.

blocks|key|4302667|text|仅仅因为malloc()是一个标准的C函数并不意味着它是对内存系统的最低级别的访问。事实上，malloc()可能是在较低级别的操作系统功能方面实现的。这意味着你也可以调用那些较低级别的接口。它们可能是特定于操作系统的，但它们可能会使您获得比malloc()界面更好的性能。如果是这样的话，你可以以任何你想要的方式实现你自己的内存分配系统，而且可能会更有效率-例如，针对你将要进行的分配的大小和频率的特征来优化算法。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|4302668|entityMap^0|4|8|1A|8|3C|8|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]|$9|K|A|L|B|C]|$9|M|A|N|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|O|8|@]|D|@]|E|$]]]|G|$]]

Just because <code>malloc()</code> is a standard C function doesn't mean that it's the lowest level access you have to the memory system. In fact, <code>malloc()</code> is probably implemented in terms of lower-level operating system functionality. That means you could call those lower level interfaces too. They might be OS-specific, but they might allow you better performance than you would get from the <code>malloc()</code> interface. If that were the case, you could implement your own memory allocation system any way you want, and maybe be even more efficient about it - optimizing the algorithm for the characteristics of the size and frequency of allocations you're going to make, for example.

blocks|key|1668716|text|当然，编写一个比通用分配程序更高效的分配器是可能的。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1668717|如果你知道你的分配的属性，你就可以把通用的分配器踢出局。|1668718|举个例子:许多年前，我们不得不为嵌入式系统设计和编码一个通信子系统(HDLC、X.25和专有层)。事实上，我们知道最大分配总是小于128字节(或类似的东西)，这意味着我们根本不必纠结于可变大小的块。不管你要求多少，每个分配都是128字节。|1668719|当然，如果您要求更多，它会返回NULL。|1668720|通过使用固定长度的块，我们能够大大加快分配和释放的速度，使用位图和相关结构来保存记帐信息，而不是依赖于速度较慢的链表。此外，不需要合并释放的块。|1668721|诚然，这是一个特例，但你会发现游戏也是如此。事实上，我们甚至在通用系统中使用了这种方法，在这种系统中，低于某个阈值的分配会以同样的方式从自我管理的预分配池中获得固定数量的内存。任何其他分配(大于阈值或池已完全分配)被发送到“真正的”malloc。|offset|length|style|CODE|1668722|entityMap^0|0|0|0|0|0|38|6|0^^$0|@$1|2|3|4|5|6|7|R|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|S|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|T|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|U|8|@]|9|@]|A|$]]|$1|H|3|I|5|6|7|V|8|@]|9|@]|A|$]]|$1|J|3|K|5|6|7|W|8|@$L|X|M|Y|N|O]]|9|@]|A|$]]|$1|P|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|Q|$]]

It's certainly possible to write an allocator more efficient than a general purpose one.

If you know the properties of your allocations, you can blow general purpose allocators out of the water.

Case in point: many years ago, we had to design and code up a communication subsystem (HDLC, X.25 and proprietary layers) for embedded systems. The fact that we knew the maximum allocation would always be less than 128 bytes (or something like that) meant that we didn't have to mess around with variable sized blocks at all. Every allocation was for 128 bytes no matter how much you asked for.

Of course, if you asked for more, it returned NULL.

By using fixed-length blocks, we were able to speed up allocations and de-allocations greatly, using bitmaps and associated structures to hold accounting information rather than relying on slower linked lists. In addition, the need to coalesce freed blocks was not needed.

Granted, this was a special case but you'll find that's so for games as well. In fact, we've even used this in a general purpose system where allocations below a certain threshold got a fixed amount of memory from a self-managed pre-allocated pool done the same way. Any other allocations (larger than the threshold or if the pool was fully allocated) were sent through to the "real" <code>malloc</code>.

blocks|key|2700333|text|通常，malloc将调用特定于操作系统的函数来获取一堆内存(至少一个VM页面)，然后根据需要将内存划分为更小的块，以返回给malloc的调用者。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2700334|malloc库还将有一个(或多个)空闲块列表，因此它通常可以满足请求，而无需请求操作系统提供更多内存。确定要处理多少不同的块大小，决定是否尝试组合相邻的空闲块，等等，这些都是malloc库实现者必须做出的选择。|2700335|您可以绕过malloc库，直接调用操作系统级别的“给我一些内存”函数，并在从操作系统获得的内存中进行自己的分配/释放。这样的实现可能是特定于操作系统的。另一种选择是使用malloc进行初始分配，但要维护自己的已释放对象缓存。|2700336|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|H|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|I|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|J|8|@]|9|@]|A|$]]|$1|F|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|G|$]]

In general, malloc will call an OS-specific function to obtain a bunch of memory (at least one VM page), and will then divide that memory up into smaller chunks as needed to return to the caller of malloc.

The malloc library will also have a list (or lists) of free blocks, so it can often meet a request without asking the OS for more memory. Determining how many different block sizes to handle, deciding whether to attempt to combine adjacent free blocks, and so forth, are the choices the malloc library implementor has to make.

It's possible for you to bypass the malloc library and directly invoke the OS-level "give me some memory" function and do your own allocation/freeing within the memory you get from the OS. Such implementations are likely to be OS-specific. Another alternative is to use malloc for initial allocations, but maintain your own cache of freed objects.

blocks|key|2700383|text|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2700384|如果我没记错的话，malloc实际上调用了一个特定于操作系统的函数|blockquote|2700385|2700386|2700387|不完全是。大多数硬件都有4KB的页面大小。操作系统通常不公开内存分配接口，它提供的内存分配接口小于页面大小(和页面对齐的)块。|2700388|malloc将大部分时间花在管理已经分配的虚拟内存空间上，只是偶尔从操作系统请求更多内存(显然，这取决于您分配的项的大小和free的频率)。|offset|length|style|CODE|2700389|有一种常见的误解，认为当您free某些东西时，它会立即返回到操作系统。虽然有时会发生这种情况(特别是对于较大的内存块)，但通常情况下，freed内存仍然分配给进程，然后可以由后来的malloc重新使用。|2700390|因此，大部分工作都是对已经分配的虚拟空间进行记账。分配策略可以有许多目标，如快速操作，低内存损耗，良好的局部性，动态增长的空间(如realloc)等。|2700391|如果您对内存分配和释放模式有更多的了解，您可以针对您的使用模式优化malloc和free，或者提供更广泛的接口。|2700392|例如，您可能正在分配大量大小相等的对象，这可能会更改最佳分配参数。或者，您可能总是一次释放大量对象，在这种情况下，您不希望free做花哨的事情。|2700393|看看memory+pools和obstacks吧。|2700394|entityMap|0|LINK|mutability|MUTABLE|url|http://en.wikipedia.org/wiki/Memory_pool|1|http://www.gnu.org/s/libc/manual/html_node/Obstacks.html^0|0|0|0|0|0|0|6|1P|4|0|D|4|1V|4|2I|6|0|1T|7|0|X|6|14|4|0|1P|4|0|2|C|0|F|8|1|0^^$0|@$1|2|3|-4|4|5|6|17|7|@]|8|@]|9|$]]|$1|A|3|B|4|C|6|18|7|@]|8|@]|9|$]]|$1|D|3|-4|4|5|6|19|7|@]|8|@]|9|$]]|$1|E|3|-4|4|5|6|1A|7|@]|8|@]|9|$]]|$1|F|3|G|4|5|6|1B|7|@]|8|@]|9|$]]|$1|H|3|I|4|5|6|1C|7|@$J|1D|K|1E|L|M]|$J|1F|K|1G|L|M]]|8|@]|9|$]]|$1|N|3|O|4|5|6|1H|7|@$J|1I|K|1J|L|M]|$J|1K|K|1L|L|M]|$J|1M|K|1N|L|M]]|8|@]|9|$]]|$1|P|3|Q|4|5|6|1O|7|@$J|1P|K|1Q|L|M]]|8|@]|9|$]]|$1|R|3|S|4|5|6|1R|7|@$J|1S|K|1T|L|M]|$J|1U|K|1V|L|M]]|8|@]|9|$]]|$1|T|3|U|4|5|6|1W|7|@$J|1X|K|1Y|L|M]]|8|@]|9|$]]|$1|V|3|W|4|5|6|1Z|7|@]|8|@$J|20|K|21|1|22]|$J|23|K|24|1|25]]|9|$]]|$1|X|3|-4|4|5|6|26|7|@]|8|@]|9|$]]]|Y|$Z|$4|10|11|12|9|$13|14]]|15|$4|10|11|12|9|$13|16]]]]

<blockquote>
 If I recall correctly, malloc actually
 calls an OS specific function
</blockquote>

Not quite. Most hardware has a 4KB page size. Operating systems generally don't expose a memory allocation interface offering anything smaller than page-sized (and page-aligned) chunks.

<code>malloc</code> spends most of its time managing the virtual memory space that has already been allocated, and only occasionally requests more memory from the OS (obviously this depends on the size of the items you allocate and how often you <code>free</code>).

There is a common misconception that when you <code>free</code> something it is immediately returned to the operating system. While this sometimes occurs (particularly for larger memory blocks) it is generally the case that <code>free</code>d memory remains allocated to the process and can then be re-used by later <code>malloc</code>s.

So most of the work is in bookkeeping of already-allocated virtual space. Allocation strategies can have many aims, such as fast operation, low memory wastage, good locality, space for dynamic growth (e.g. <code>realloc</code>) and so on.

If you know more about your pattern of memory allocation and release, you can optimise <code>malloc</code> and <code>free</code> for your usage patterns or provide a more extensive interface.

For instance, you may be allocating lots of equal-sized objects, which may change the optimal allocation parameters. Or you may always free large amounts of objects at once, in which case you don't want <code>free</code> to be doing fancy things.

Have a look at <a href="http://en.wikipedia.org/wiki/Memory_pool" rel="nofollow">memory pools</a> and <a href="http://www.gnu.org/s/libc/manual/html_node/Obstacks.html" rel="nofollow">obstacks</a>.

I read that some games rewrite their own malloc to be more efficient. I don't understand how this is possible in a virtual memory world. If I recall correctly, malloc actually calls an OS specific function, which maps the virtual address to a real address with the MMU. So then how can someone make their own memory allocator and allocate real memory, without calling the actual runtime's malloc?

Thanks

making your own malloc function?

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我读到一些游戏重写了他们自己的malloc以提高效率。我不明白在虚拟内存的世界里这怎么可能。如果我没记错的话，malloc实际上调用了一个特定于操作系统的函数，该函数使用MMU将虚拟地址映射到真实地址。那么，如何在不调用实际运行时的malloc的情况下，创建自己的内存分配器并分配实际内存呢？谢谢

问让你自己的malloc函数？
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问让你自己的malloc函数？EN