On Wed 21-12-16 00:31:47, Tetsuo Handa wrote:
> Michal Hocko wrote:
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index c8eed66d8abb..2dda7c3eba52 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -3098,32 +3098,31 @@ __alloc_pages_may_oom(gfp_t gfp_mask, unsigned int order,
> > if (page)
> > goto out;
> >
> > - if (!(gfp_mask & __GFP_NOFAIL)) {
> > - /* Coredumps can quickly deplete all memory reserves */
> > - if (current->flags & PF_DUMPCORE)
> > - goto out;
> > - /* The OOM killer will not help higher order allocs */
> > - if (order > PAGE_ALLOC_COSTLY_ORDER)
> > - goto out;
> > - /* The OOM killer does not needlessly kill tasks for lowmem */
> > - if (ac->high_zoneidx < ZONE_NORMAL)
> > - goto out;
> > - if (pm_suspended_storage())
> > - goto out;
> > - /*
> > - * XXX: GFP_NOFS allocations should rather fail than rely on
> > - * other request to make a forward progress.
> > - * We are in an unfortunate situation where out_of_memory cannot
> > - * do much for this context but let's try it to at least get
> > - * access to memory reserved if the current task is killed (see
> > - * out_of_memory). Once filesystems are ready to handle allocation
> > - * failures more gracefully we should just bail out here.
> > - */
> > + /* Coredumps can quickly deplete all memory reserves */
> > + if (current->flags & PF_DUMPCORE)
> > + goto out;
> > + /* The OOM killer will not help higher order allocs */
> > + if (order > PAGE_ALLOC_COSTLY_ORDER)
> > + goto out;
> > + /* The OOM killer does not needlessly kill tasks for lowmem */
> > + if (ac->high_zoneidx < ZONE_NORMAL)
> > + goto out;
> > + if (pm_suspended_storage())
> > + goto out;
> > + /*
> > + * XXX: GFP_NOFS allocations should rather fail than rely on
> > + * other request to make a forward progress.
> > + * We are in an unfortunate situation where out_of_memory cannot
> > + * do much for this context but let's try it to at least get
> > + * access to memory reserved if the current task is killed (see
> > + * out_of_memory). Once filesystems are ready to handle allocation
> > + * failures more gracefully we should just bail out here.
> > + */
> > +
> > + /* The OOM killer may not free memory on a specific node */
> > + if (gfp_mask & __GFP_THISNODE)
> > + goto out;
> >
> > - /* The OOM killer may not free memory on a specific node */
> > - if (gfp_mask & __GFP_THISNODE)
> > - goto out;
> > - }
> > /* Exhausted what can be done so it's blamo time */
> > if (out_of_memory(&oc) || WARN_ON_ONCE(gfp_mask & __GFP_NOFAIL)) {
> > *did_some_progress = 1;
>
> Why do we need to change this part in this patch?
>
> This change silently prohibits invoking the OOM killer for e.g. costly
> GFP_KERNEL allocation.
We have never allowed coslty GFP_KERNEL requests to invoke the oom
killer. And there is a good reason for it which is even mentioned in the
changelog. The only change here is that GFP_NOFAIL doesn't override this
decision - again for reasons mentioned in the changelog.
> While it would be better if vmalloc() can be used,
> there might be users who cannot accept vmalloc() as a fallback (e.g.
> CONFIG_MMU=n where vmalloc() == kmalloc() ?).
I haven't ever heard any complains about this in the past. If there is a
valid usecase then we can treat nommu specialy. That would require more
changes though.
> This change is not "do not enforce OOM killer automatically" but
> "never allow OOM killer". No exception is allowed. If we change
> this part, title for this part should be something strong like
> "mm,oom: Never allow OOM killer for coredumps, costly allocations,
> lowmem etc.".
Sigh. We didn't allow the oom killer for all those cases and the only
thing that is changed here is to not override those decisions with
__GFP_NOFAIL which is imho reflected in the title. If that is not clear
then I would suggest "mm, oom: do not override OOM killer decisions with
__GFP_NOFAIL".
--
Michal Hocko
SUSE Labs
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