linux-kernel - Re: [PATCH] mm,oom: fix oom invocation issues

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Message-Id: <201705182257.HJJ52185.OQStFLFMHVOJOF@I-love.SAKURA.ne.jp>
Date:   Thu, 18 May 2017 22:57:10 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:     mhocko@...nel.org
Cc:     guro@...com, hannes@...xchg.org, vdavydov.dev@...il.com,
        kernel-team@...com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm,oom: fix oom invocation issues

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().