I had a chat on #mm channel with hnaz about task_struct's member children and sibling list head:

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macli I am newbie, and reading mm/oom_kill.c, wondering why list_for_each_entry(child, &p->children, sibling) in badness(), not list_for_each_entry(child, &p->children, children)?

hnaz macli: it's the linkname.  task->children is the head of a list that is linked by task->sibling

macli hnaz: I see #define list_for_each_entry(pos, head, member) in list.h,  where I can find the code that task->children ,the list head which is linked by task->sibling, I see struct task_struct has two list_head children and silbling

macli struct list_head children;      /* list of my children */

macli struct list_head sibling;       /* linkage in my parent's children list */

macli I am assuming that children is the list head of a task's children list

macli sibling is the list head of a task's parent's children list which is different with the children list head, that is my understanding of reading the comment

hnaz macli: you have to understand that a 'list_head' is at the same time a node.  it represents one link in the list

hnaz macli: children is the link to other task structs that represent the children

hnaz macli: while sibling is the link to chain up a task as part of another task's children list

macli hnaz: I see, thanks for the explaintion