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SubjectRe: Linux 5.0-rc1 (test results)
On Wed 09-01-19 00:16:59, Guo Ren wrote:
> 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);
> }

Btw. we have that nice documentation in gfp.h. I would encourage you to
read through that rather than try to imply the semantic from the
implementation.

> 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.

OK

--
Michal Hocko
SUSE Labs

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