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SubjectRe: [PATCH v1] kernel/trace:check the val against the available mem
On Wed 04-04-18 10:11:49, Steven Rostedt wrote:
> On Wed, 4 Apr 2018 08:23:40 +0200
> Michal Hocko <mhocko@kernel.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.

Well, you would need to do something like:

>
> 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;

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

If you use __GFP_RETRY_MAYFAIL it would have to be somedy else to
trigger the OOM killer and this user context would get killed. If you
drop __GFP_RETRY_MAYFAIL it would be this context to trigger the OOM but
it would still be the selected victim.
--
Michal Hocko
SUSE Labs

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