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 " 2 2 2 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
