linux-kernel - Re: [PATCH v1] kernel/trace:check the val against the available mem

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Date:   Wed, 4 Apr 2018 10:11:49 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Zhaoyang Huang <huangzhaoyang@...il.com>,
        Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
        kernel-patch-test@...ts.linaro.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Joel Fernandes <joelaf@...gle.com>, linux-mm@...ck.org,
        Vlastimil Babka <vbabka@...e.cz>
Subject: Re: [PATCH v1] kernel/trace:check the val against the available mem

On Wed, 4 Apr 2018 08:23:40 +0200
Michal Hocko <mhocko@...nel.org> wrote:

> If you are afraid of that then you can have a look at {set,clear}_current_oom_origin()
> which will automatically select the current process as an oom victim and
> kill it.

Would it even receive the signal? Does alloc_pages_node() even respond
to signals? Because the OOM happens while the allocation loop is
running.

I tried it out, I did the following:

	set_current_oom_origin();
	for (i = 0; i < nr_pages; i++) {
		struct page *page;
		/*
		 * __GFP_RETRY_MAYFAIL flag makes sure that the allocation fails
		 * gracefully without invoking oom-killer and the system is not
		 * destabilized.
		 */
		bpage = kzalloc_node(ALIGN(sizeof(*bpage), cache_line_size()),
				    GFP_KERNEL | __GFP_RETRY_MAYFAIL,
				    cpu_to_node(cpu));
		if (!bpage)
			goto free_pages;

		list_add(&bpage->list, pages);

		page = alloc_pages_node(cpu_to_node(cpu),
					GFP_KERNEL | __GFP_RETRY_MAYFAIL, 0);
		if (!page)
			goto free_pages;
		bpage->page = page_address(page);
		rb_init_page(bpage->page);
	}
	clear_current_oom_origin();

The first time I ran my ring buffer memory stress test, it killed the
stress test. The second time I ran it, it killed polkitd.

Still doesn't help as much as the original patch.

You haven't convinced me that using si_mem_available() is a bad idea.
If anything, you've solidified my confidence in it.

-- Steve