【Linux 内核内存管理】物理分配页 ⑨ (

2023-04-19 13:03| 来源: 网络整理| 查看: 265

文章目录一、retry 标号代码分析二、retry 标号完整代码

在【Linux 内核内存管理】物理分配页 ② ( __alloc_pages_nodemask 函数参数分析 | __alloc_pages_nodemask 函数分配物理页流程 ) 博客中 , 分析了 __alloc_pages_nodemask 函数分配物理页流程如下 :

首先 , 根据 gfp_t gfp_mask 分配标志位参数 , 得到 " 内存节点 “ 的首选 ” 区域类型 " 和 " 迁移类型 " ;

然后 , 执行 " 快速路径 " , 第一次分配尝试使用低水线分配 ;

如果上述 " 快速路径 " 分配失败 , 则执行 " 慢速路径 " 分配 ;

上述涉及到了 " 快速路径 " 和 " 慢速路径 "

种物理页分配方式 ;

继续接着上一篇博客【Linux 内核内存管理】物理分配页 ⑧ ( __alloc_pages_slowpath 慢速路径调用函数源码分析 | 获取首选内存区域 | 异步回收内存页 | 最低水线也分配 | 直接分配 ) 分析 __alloc_pages_slowpath 慢速路径内存分配调用函数的后续部分源码 ;

一、retry 标号代码分析

下面开始分析 __alloc_pages_slowpath 慢速路径内存分配调用函数中的 retry 标号下的代码 ,

调用 wake_all_kswapds 函数 , 确保 " 页回收线程 " 在遍历时保持唤醒状态 , 不会由于意外导致休眠 ;

retry: /* Ensure kswapd doesn't accidentally go to sleep as long as we loop */ if (gfp_mask & __GFP_KSWAPD_RECLAIM) wake_all_kswapds(order, ac);

源码路径 : linux-4.12\mm\page_alloc.c#3794

调用 get_page_from_freelist 函数 , 尝试使用调整过的区域列表和分配标志位进行内存分配 , 如果内存分配成功 , 则跳转到 got_pg 标号执行 ;

/* Attempt with potentially adjusted zonelist and alloc_flags */ page = get_page_from_freelist(gfp_mask, order, alloc_flags, ac); if (page) goto got_pg;

源码路径 : linux-4.12\mm\page_alloc.c#3811

如果调用者不想等待浪费时间 , 则不执行后续操作 , 跳转到 nopage 处执行后续代码 ;

/* Caller is not willing to reclaim, we can't balance anything */ if (!can_direct_reclaim) goto nopage;

源码路径 : linux-4.12\mm\page_alloc.c#3817

调用 __alloc_pages_direct_reclaim 函数 , 直接进行页回收 ;

/* Try direct reclaim and then allocating */ page = __alloc_pages_direct_reclaim(gfp_mask, order, alloc_flags, ac, &did_some_progress); if (page) goto got_pg;

源码路径 : linux-4.12\mm\page_alloc.c#3833

调用 __alloc_pages_direct_compact 函数 , 针对申请物理页阶数大于 0 的情况 , 执行同步模式下的内存碎片整理操作 ;

/* Try direct compaction and then allocating */ page = __alloc_pages_direct_compact(gfp_mask, order, alloc_flags, ac, compact_priority, &compact_result); if (page) goto got_pg;

源码路径 : linux-4.12\mm\page_alloc.c#3839

再次进行判断 , 如果调用者不想进行循环 , 则放弃内存申请 , 跳转到 nopage 标号执行 ;

/* Do not loop if specifically requested */ if (gfp_mask & __GFP_NORETRY) goto nopage;

源码路径 : linux-4.12\mm\page_alloc.c#3845

如果申请物理页阶数大于 0 , 则调用 should_compact_retry 函数 , 判断是否重新尝试执行内存碎片整理操作 , 如果判定成功 , 则继续跳转到 retry 标号处再执行一遍 ;

/* * It doesn't make any sense to retry for the compaction if the order-0 * reclaim is not able to make any progress because the current * implementation of the compaction depends on the sufficient amount * of free memory (see __compaction_suitable) */ if (did_some_progress > 0 && should_compact_retry(ac, order, alloc_flags, compact_result, &compact_priority, &compaction_retries)) goto retry;

源码路径 : linux-4.12\mm\page_alloc.c#3865

调用 read_mems_allowed_retry 函数 , 判定 cpuset 是否允许修改当前进程从指定的内存节点申请物理页内存 ;

/* * It's possible we raced with cpuset update so the OOM would be * premature (see below the nopage: label for full explanation). */ if (read_mems_allowed_retry(cpuset_mems_cookie)) goto retry_cpuset;

源码路径 : linux-4.12\mm\page_alloc.c#3875

调用 __alloc_pages_may_oom 函数 , 如果内存耗尽 , 分配内存失败 , 则杀死一个进程 , 以获取足够的内存空间 ;

/* Reclaim has failed us, start killing things */ page = __alloc_pages_may_oom(gfp_mask, order, ac, &did_some_progress); if (page) goto got_pg;

源码路径 : linux-4.12\mm\page_alloc.c#3879

假如当前进程出现内存耗尽的情况 , 则忽略最低水线的限制 , 或者不允许使用紧急保留内存 ;

/* Avoid allocations with no watermarks from looping endlessly */ if (test_thread_flag(TIF_MEMDIE) && (alloc_flags == ALLOC_NO_WATERMARKS || (gfp_mask & __GFP_NOMEMALLOC))) goto nopage;

源码路径 : linux-4.12\mm\page_alloc.c#3884

内存耗尽杀手取得一定进展 , 继续跳转到 retry 标号重新尝试分配内存 ;

/* Retry as long as the OOM killer is making progress */ if (did_some_progress) { no_progress_loops = 0; goto retry; }

源码路径 : linux-4.12\mm\page_alloc.c#3890

二、retry 标号完整代码

retry 标号完整代码 :

static inline struct page * __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order, struct alloc_context *ac) { ... retry: /* Ensure kswapd doesn't accidentally go to sleep as long as we loop */ if (gfp_mask & __GFP_KSWAPD_RECLAIM) wake_all_kswapds(order, ac); if (gfp_pfmemalloc_allowed(gfp_mask)) alloc_flags = ALLOC_NO_WATERMARKS; /* * Reset the zonelist iterators if memory policies can be ignored. * These allocations are high priority and system rather than user * orientated. */ if (!(alloc_flags & ALLOC_CPUSET) || (alloc_flags & ALLOC_NO_WATERMARKS)) { ac->zonelist = node_zonelist(numa_node_id(), gfp_mask); ac->preferred_zoneref = first_zones_zonelist(ac->zonelist, ac->high_zoneidx, ac->nodemask); } /* Attempt with potentially adjusted zonelist and alloc_flags */ page = get_page_from_freelist(gfp_mask, order, alloc_flags, ac); if (page) goto got_pg; /* Caller is not willing to reclaim, we can't balance anything */ if (!can_direct_reclaim) goto nopage; /* Make sure we know about allocations which stall for too long */ if (time_after(jiffies, alloc_start + stall_timeout)) { warn_alloc(gfp_mask & ~__GFP_NOWARN, ac->nodemask, "page allocation stalls for %ums, order:%u", jiffies_to_msecs(jiffies-alloc_start), order); stall_timeout += 10 * HZ; } /* Avoid recursion of direct reclaim */ if (current->flags & PF_MEMALLOC) goto nopage; /* Try direct reclaim and then allocating */ page = __alloc_pages_direct_reclaim(gfp_mask, order, alloc_flags, ac, &did_some_progress); if (page) goto got_pg; /* Try direct compaction and then allocating */ page = __alloc_pages_direct_compact(gfp_mask, order, alloc_flags, ac, compact_priority, &compact_result); if (page) goto got_pg; /* Do not loop if specifically requested */ if (gfp_mask & __GFP_NORETRY) goto nopage; /* * Do not retry costly high order allocations unless they are * __GFP_REPEAT */ if (costly_order && !(gfp_mask & __GFP_REPEAT)) goto nopage; if (should_reclaim_retry(gfp_mask, order, ac, alloc_flags, did_some_progress > 0, &no_progress_loops)) goto retry; /* * It doesn't make any sense to retry for the compaction if the order-0 * reclaim is not able to make any progress because the current * implementation of the compaction depends on the sufficient amount * of free memory (see __compaction_suitable) */ if (did_some_progress > 0 && should_compact_retry(ac, order, alloc_flags, compact_result, &compact_priority, &compaction_retries)) goto retry; /* * It's possible we raced with cpuset update so the OOM would be * premature (see below the nopage: label for full explanation). */ if (read_mems_allowed_retry(cpuset_mems_cookie)) goto retry_cpuset; /* Reclaim has failed us, start killing things */ page = __alloc_pages_may_oom(gfp_mask, order, ac, &did_some_progress); if (page) goto got_pg; /* Avoid allocations with no watermarks from looping endlessly */ if (test_thread_flag(TIF_MEMDIE) && (alloc_flags == ALLOC_NO_WATERMARKS || (gfp_mask & __GFP_NOMEMALLOC))) goto nopage; /* Retry as long as the OOM killer is making progress */ if (did_some_progress) { no_progress_loops = 0; goto retry; } ... }

源码路径 : linux-4.12\mm\page_alloc.c#3792

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【Linux 内核 内存管理】物理分配页 ⑨ (

【Linux 内核内存管理】物理分配页 ⑨ (