libc malloc vs linux 内核伙伴分配器
libc malloc vs linux kernel buddy allocator
malloc 是否担心 linux 内核中的内部碎片？
例如，当我想分配 5 个页面时，malloc 会向上舍入大小使其成为 2 的幂：5->8 以避免内核中的内部碎片，因为 linux 内核使用伙伴系统作为页面分配器。
至少对于 glibc 来说，它并不真正关心内核中的碎片。它主要是一个 "best-fit" 分配器，除了非常小或非常大的分配。这是 glibc 的“malloc.c”顶部附近评论的摘录：
Why use this malloc?
This is not the fastest, most space-conserving, most portable, or
most tunable malloc ever written. However it is among the fastest
while also being among the most space-conserving, portable and tunable.
Consistent balance across these factors results in a good general-purpose
allocator for malloc-intensive programs.
The main properties of the algorithms are:
- For large (>= 512 bytes) requests, it is a pure best-fit allocator,
with ties normally decided via FIFO (i.e. least recently used).
- For small (<= 64 bytes by default) requests, it is a caching
allocator, that maintains pools of quickly recycled chunks.
- In between, and for combinations of large and small requests, it does
the best it can trying to meet both goals at once.
- For very large requests (>= 128KB by default), it relies on system
memory mapping facilities, if supported.
For a longer but slightly out of date high-level description, see
http://gee.cs.oswego.edu/dl/html/malloc.html
glibc malloc 实现可以使用 mallopt 函数或各种环境变量来设置各种参数，如手册页 mallopt(3) 中所述。
malloc 是否担心 linux 内核中的内部碎片？ 例如，当我想分配 5 个页面时，malloc 会向上舍入大小使其成为 2 的幂：5->8 以避免内核中的内部碎片，因为 linux 内核使用伙伴系统作为页面分配器。
至少对于 glibc 来说，它并不真正关心内核中的碎片。它主要是一个 "best-fit" 分配器，除了非常小或非常大的分配。这是 glibc 的“malloc.c”顶部附近评论的摘录：
Why use this malloc?
This is not the fastest, most space-conserving, most portable, or most tunable malloc ever written. However it is among the fastest while also being among the most space-conserving, portable and tunable. Consistent balance across these factors results in a good general-purpose allocator for malloc-intensive programs. The main properties of the algorithms are:
- For large (>= 512 bytes) requests, it is a pure best-fit allocator, with ties normally decided via FIFO (i.e. least recently used).
- For small (<= 64 bytes by default) requests, it is a caching allocator, that maintains pools of quickly recycled chunks.
- In between, and for combinations of large and small requests, it does the best it can trying to meet both goals at once.
- For very large requests (>= 128KB by default), it relies on system memory mapping facilities, if supported.
For a longer but slightly out of date high-level description, see http://gee.cs.oswego.edu/dl/html/malloc.html
glibc malloc 实现可以使用 mallopt 函数或各种环境变量来设置各种参数，如手册页 mallopt(3) 中所述。