linux-kernel - Re: Linux 5.0-rc1 (test results)

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Date:   Wed, 9 Jan 2019 00:16:59 +0800
From:   Guo Ren <guoren@...nel.org>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>
Subject: Re: Linux 5.0-rc1 (test results)

Thx Michal,

On Tue, Jan 08, 2019 at 04:40:31PM +0100, Michal Hocko wrote:
> On Tue 08-01-19 17:51:07, Guo Ren wrote:
> [...]
> > static inline pte_t *pte_alloc_one_kernel(struct mm_struct *mm)
> > {
> > 	pte_t *pte;
> > 	unsigned long i;
> > 
> > 	pte = (pte_t *) __get_free_page(GFP_KERNEL | __GFP_RETRY_MAYFAIL);
> > 						     ^^^^^^^^^^^^^^^^^^^
> > 						     It's necessary ?
> > 						     x86 & arm don't use
> > 						     it.
> > 	if (!pte)
> > 		return NULL;
> 
> That depends on whether you want OOM killer to be triggered for these
> allocations. If you add the flag then the allocation bails out with a
> failure rather than kill an oom victim.

Yes, in page_alloc.c: 
	if (gfp_mask & __GFP_RETRY_MAYFAIL)
		goto out;
	...
	if (out_of_memory(&oc) || WARN_ON_ONCE(gfp_mask & __GFP_NOFAIL)) {
            ^^^^^^^^^^^^^ OOM kill victim
	...
		if (gfp_mask & __GFP_NOFAIL)
			page = __alloc_pages_cpuset_fallback(gfp_mask, order,
					ALLOC_NO_WATERMARKS, ac);
	}

Seems it could affect the behavior of the system which is out of memory.
OOM killer could help to get_page for current. So keep the same as x86 &
arm here. I'll remove __GFP_RETRY_MAYFAIL in patch.

Best Regards
 Guo Ren