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

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Date:   Wed, 4 Apr 2018 11:47:30 -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 16:23:29 +0200
Michal Hocko <mhocko@...nel.org> wrote:

> > 
> > 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;  
> 
> 		if (fatal_signal_pending())
> 			fgoto free_pages;

I originally was going to remove the RETRY_MAYFAIL, but adding this
check (at the end of the loop though) appears to have OOM consistently
kill this task.

I still like to keep RETRY_MAYFAIL, because it wont trigger OOM if
nothing comes in and tries to do an allocation, but instead will fail
nicely with -ENOMEM.

-- Steve


> 
> > 		bpage->page = page_address(page);
> > 		rb_init_page(bpage->page);
> > 	}
> > 	clear_current_oom_origin();