Re: [PATCH] mm,oom: fix oom invocation issues

From: Tetsuo Handa
Date: Thu May 18 2017 - 09:57:34 EST

Michal Hocko wrote:
> It is racy and it basically doesn't have any allocation context so we
> might kill a task from a different domain. So can we do this instead?
> There is a slight risk that somebody might have returned VM_FAULT_OOM
> without doing an allocation but from my quick look nobody does that
> currently.

I can't tell whether it is safe to remove out_of_memory() from pagefault_out_of_memory().
There are VM_FAULT_OOM users in fs/ directory. What happens if pagefault_out_of_memory()
was called as a result of e.g. GFP_NOFS allocation failure? Is it guaranteed that all
memory allocations that might occur from page fault event (or any action that might return
VM_FAULT_OOM) are allowed to call oom_kill_process() from out_of_memory() before
reaching pagefault_out_of_memory() ?

Anyway, I want

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

so that we won't see similar backtraces and memory information from both
out_of_memory() and warn_alloc().