diff --git a/study/kernel/02-memory/04-buddy/04-alloc_page/README.md b/study/kernel/02-memory/04-buddy/04-alloc_page/README.md index ea4217d..fe722d7 100755 --- a/study/kernel/02-memory/04-buddy/04-alloc_page/README.md +++ b/study/kernel/02-memory/04-buddy/04-alloc_page/README.md @@ -511,9 +511,14 @@ for 循环所作的基本上与直觉一致(从高端向低端扫描), for_next_ * 首先, 如果使能了 CPUSET, 且内存分配附带了 ALLOC_CPUSET 标记, 则只能(从 CPUSET 限定的)该进程允许运行 CPU 的所属内存域去分配内存, 通过 `__cpuset_zone_allowed` 来检查. -* `zone_watermark_fast` 检测当前 `ZONE` 的水位情况, 检查是否能够满足当前多个页面的分配请求. 如果水位不足, 则会 `zone_reclaim` 尝试去回收内存. 如果没有正常回收, 或者回收的内存不够, 都将跳过从 ZONE 上分配内存, 回收完成后, 通过 `zone_watermark_ok` 当前 ZONE 是否(回收够了)足够的空闲页. +* `zone_watermark_fast` 检测当前 `ZONE` 的水位情况, 检查是否能够满足当前多个页面的分配请求. 如果水位不足, 则会 `zone_reclaim` 尝试去回收内存. 如果没有正常回收, 或者回收的内存不够, 都将跳过从 ZONE 上分配内存, 回收完成后, 通过 `zone_watermark_ok` 再次检查 ZONE 的水位情况以及是否满足连续大内存块的分配需求. + +* 如果没有足够的空闲页, 或者没有连续内存块可满足分配请求, 则循环进行到备用列表中的下一个内存域, 继续同样的检查. 直到找到一个合适的页面, 再进行 `try_this_node` 进行内存分配. 请注意即使一切检查都成功了, 最终依然可能会分配失败. 这种情况可能是: + + 1. 外碎片化严重, 没有足够的连续内存页 + + 2. 也可能是无法从 ZONE 内其他迁移类型中借用内存出来. -* 如果没有足够的空闲页, 或者没有连续内存块可满足分配请求, 则循环进行到备用列表中的下一个内存域, 作同样的检查. 直到找到一个合适的页面, 再进行 `try_this_node` 进行内存分配. * 如果内存域适用于当前的分配请求, 那么则通过 `rmqueue` 从伙伴系统中分配内存. @@ -674,8 +679,6 @@ try_this_zone: } ``` -其中 zone_watermark_fast 函数检查当前 ZONE 中的水位情况 - ## 3.3 水位控制 ------- @@ -890,3 +893,47 @@ for (o = order; o < MAX_ORDER; o++) { ### 3.3.3 zone_watermark_fast ------- + + +## 3.4 rmqueue +------- + +### 3.4.1 rmqueue 的基本流程 + +![rmqueue 流程](./rmqueue.png) + + +```cpp +// https://elixir.bootlin.com/linux/v5.10/source/mm/page_alloc.c#L3421 +``` + +1. 对于分配分配单页的情况(oder == 0), 则使用 [`rmqueue_pcplist`](https://elixir.bootlin.com/linux/v5.10/source/mm/page_alloc.c#L3396) 直接从冷热页缓存 PCP(Per Cpu Pages)中获取. + +2. 如果设置了 ALLOC_HARDER, 则说明是一次高优先级的分配, 就[从迁移类型为 MIGRATE_HIGHATOMIC 的内存中进行分配](https://elixir.bootlin.com/linux/v5.10/source/mm/page_alloc.c#3458). MIGRATE_HIGHATOMIC 类型的页用常用于于一些紧急情况下的内存分配. + +3. 常规模式下, 一般都是通过 [`__rmqueue`](https://elixir.bootlin.com/linux/v5.10/source/mm/page_alloc.c#L2841) 从伙伴系统中指定迁移类型为 migratetype 的链表中获取. + + 3.1 如果超过一半空闲内存位于 CMA 区域时, 则优先使用 [`__rmqueue_cma_fallback`](https://elixir.bootlin.com/linux/v5.10/source/mm/page_alloc.c#L2348) 从 CMA 中分配 + + 3.2 标准流程就是 [`__rmqueue_smallest`](https://elixir.bootlin.com/linux/v5.10/source/mm/page_alloc.c#L2348) 从 各个 order 的空闲链表中获取, 首先从当前 order 的空闲链表中获取页面, 如果当前 order 页面不足, 则开始向高 order 的链表中切蛋糕. + + 3.3 如果切蛋糕也失败了, 说明空闲的页面已经不足以支撑此次分配, 则从 CMA 区域中预留的内存中进行分配. + + 3.4 如果前面流程都失败了, 那么说明当前 MIGRATE_TYPE 中已经没有足够的连续物理页面, 那么进入 fallback 流程, 尝试从其他 MIGRATE_TYPE 中窃取内存. + + +4. 通过 [`check_new_pages`](https://elixir.bootlin.com/linux/v5.10/source/mm/page_alloc.c#L2253) 检查获取到的内存页是否满足要求. 伙伴系统返回了所获取的的物理页面块第一个页面的 page 结构体, 而 [`check_new_pages`](https://elixir.bootlin.com/linux/v5.10/source/mm/page_alloc.c#L2253) 则需要检查所有的页面. + + +### 3.4.2 rmqueue_pcplist +------- + +### 3.4.3 ` __rmqueue` +------- 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