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SubjectRe: [PATCH] ring-buffer: Add set/clear_current_oom_origin() during allocations
On Wed, 4 Apr 2018 11:53:10 -0400
Steven Rostedt <rostedt@goodmis.org> wrote:

> @@ -1162,35 +1163,60 @@ static int rb_check_pages(struct ring_buffer_per_cpu *cpu_buffer)
> static int __rb_allocate_pages(long nr_pages, struct list_head *pages, int cpu)
> {
> struct buffer_page *bpage, *tmp;
> + bool user_thread = current->mm != NULL;
> + gfp_t mflags;
> long i;
>
> - /* Check if the available memory is there first */
> + /*
> + * Check if the available memory is there first.
> + * Note, si_mem_available() only gives us a rough estimate of available
> + * memory. It may not be accurate. But we don't care, we just want
> + * to prevent doing any allocation when it is obvious that it is
> + * not going to succeed.
> + */

In case you are wondering how I tested this, I simply added:

#if 0
> i = si_mem_available();
> if (i < nr_pages)
> return -ENOMEM;
#endif

for the tests. Note, without this, I tried to allocate all memory
(bisecting it with allocations that failed and allocations that
succeeded), and couldn't trigger an OOM :-/

Of course, this was on x86_64, where I'm sure I could allocate
any memory, and probably would have had more luck with a 32bit kernel
using higmem.

-- Steve

>
> + /*
> + * __GFP_RETRY_MAYFAIL flag makes sure that the allocation fails
> + * gracefully without invoking oom-killer and the system is not
> + * destabilized.
> + */
> + mflags = GFP_KERNEL | __GFP_RETRY_MAYFAIL;
> +
> + /*
> + * If a user thread allocates too much, and si_mem_available()
> + * reports there's enough memory, even though there is not.
> + * Make sure the OOM killer kills this thread. This can happen
> + * even with RETRY_MAYFAIL because another task may be doing
> + * an allocation after this task has taken all memory.
> + * This is the task the OOM killer needs to take out during this
> + * loop, even if it was triggered by an allocation somewhere else.
> + */
> + if (user_thread)
> + 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));
> + mflags, 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);
> + page = alloc_pages_node(cpu_to_node(cpu), mflags, 0);
> if (!page)
> goto free_pages;
> bpage->page = page_address(page);
> rb_init_page(bpage->page);
> +
> + if (user_thread && fatal_signal_pending(current))
> + goto free_pages;
> }
> + if (user_thread)
> + clear_current_oom_origin();
>
> return 0;
>
> @@ -1199,6 +1225,8 @@ static int __rb_allocate_pages(long nr_pages, struct list_head *pages, int cpu)
> list_del_init(&bpage->list);
> free_buffer_page(bpage);
> }
> + if (user_thread)
> + clear_current_oom_origin();
>
> return -ENOMEM;
> }

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