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Re: [PATCH 2/3] mm, oom: do not enfore OOM killer for __GFP_NOFAIL automatically

Started by"Hillf Danton" <hillf.zj@alibaba-inc.com>
First post2017-01-20 09:40 +0100
Last post2017-01-25 11:30 +0100
Articles 6 — 2 participants

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  Re: [PATCH 2/3] mm, oom: do not enfore OOM killer for __GFP_NOFAIL automatically "Hillf Danton" <hillf.zj@alibaba-inc.com> - 2017-01-20 09:40 +0100
    Re: [PATCH 2/3] mm, oom: do not enfore OOM killer for __GFP_NOFAIL  automatically Michal Hocko <mhocko@kernel.org> - 2017-01-24 13:50 +0100
      Re: [PATCH 2/3] mm, oom: do not enfore OOM killer for __GFP_NOFAIL automatically "Hillf Danton" <hillf.zj@alibaba-inc.com> - 2017-01-25 08:10 +0100
        Re: [PATCH 2/3] mm, oom: do not enfore OOM killer for __GFP_NOFAIL  automatically Michal Hocko <mhocko@kernel.org> - 2017-01-25 09:10 +0100
          Re: [PATCH 2/3] mm, oom: do not enfore OOM killer for __GFP_NOFAIL automatically "Hillf Danton" <hillf.zj@alibaba-inc.com> - 2017-01-25 09:50 +0100
            Re: [PATCH 2/3] mm, oom: do not enfore OOM killer for __GFP_NOFAIL  automatically Michal Hocko <mhocko@kernel.org> - 2017-01-25 11:30 +0100

#1563382 — Re: [PATCH 2/3] mm, oom: do not enfore OOM killer for __GFP_NOFAIL automatically

From"Hillf Danton" <hillf.zj@alibaba-inc.com>
Date2017-01-20 09:40 +0100
SubjectRe: [PATCH 2/3] mm, oom: do not enfore OOM killer for __GFP_NOFAIL automatically
Message-ID<t1CTM-4W3-17@gated-at.bofh.it>
On Tuesday, December 20, 2016 9:49 PM Michal Hocko wrote: 
> 
> @@ -1013,7 +1013,7 @@ bool out_of_memory(struct oom_control *oc)
>  	 * make sure exclude 0 mask - all other users should have at least
>  	 * ___GFP_DIRECT_RECLAIM to get here.
>  	 */
> -	if (oc->gfp_mask && !(oc->gfp_mask & (__GFP_FS|__GFP_NOFAIL)))
> +	if (oc->gfp_mask && !(oc->gfp_mask & __GFP_FS))
>  		return true;
> 
As to GFP_NOFS|__GFP_NOFAIL request, can we check gfp mask
one bit after another?

	if (oc->gfp_mask) {
		if (!(oc->gfp_mask & __GFP_FS))
			return false;

		/* No service for request that can handle fail result itself */
		if (!(oc->gfp_mask & __GFP_NOFAIL))
			return false;
	}

thanks
Hillf

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#1565828 — Re: [PATCH 2/3] mm, oom: do not enfore OOM killer for __GFP_NOFAIL automatically

FromMichal Hocko <mhocko@kernel.org>
Date2017-01-24 13:50 +0100
SubjectRe: [PATCH 2/3] mm, oom: do not enfore OOM killer for __GFP_NOFAIL automatically
Message-ID<t38HT-4mc-11@gated-at.bofh.it>
In reply to#1563382
On Fri 20-01-17 16:33:36, Hillf Danton wrote:
> 
> On Tuesday, December 20, 2016 9:49 PM Michal Hocko wrote: 
> > 
> > @@ -1013,7 +1013,7 @@ bool out_of_memory(struct oom_control *oc)
> >  	 * make sure exclude 0 mask - all other users should have at least
> >  	 * ___GFP_DIRECT_RECLAIM to get here.
> >  	 */
> > -	if (oc->gfp_mask && !(oc->gfp_mask & (__GFP_FS|__GFP_NOFAIL)))
> > +	if (oc->gfp_mask && !(oc->gfp_mask & __GFP_FS))
> >  		return true;
> > 
> As to GFP_NOFS|__GFP_NOFAIL request, can we check gfp mask
> one bit after another?
> 
> 	if (oc->gfp_mask) {
> 		if (!(oc->gfp_mask & __GFP_FS))
> 			return false;
> 
> 		/* No service for request that can handle fail result itself */
> 		if (!(oc->gfp_mask & __GFP_NOFAIL))
> 			return false;
> 	}

I really do not understand this request. This patch is removing the
__GFP_NOFAIL part... Besides that why should they return false?
-- 
Michal Hocko
SUSE Labs

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#1566352

From"Hillf Danton" <hillf.zj@alibaba-inc.com>
Date2017-01-25 08:10 +0100
Message-ID<t3pSp-76h-3@gated-at.bofh.it>
In reply to#1565828
On Tuesday, January 24, 2017 8:41 PM Michal Hocko wrote: 
> On Fri 20-01-17 16:33:36, Hillf Danton wrote:
> >
> > On Tuesday, December 20, 2016 9:49 PM Michal Hocko wrote:
> > >
> > > @@ -1013,7 +1013,7 @@ bool out_of_memory(struct oom_control *oc)
> > >  	 * make sure exclude 0 mask - all other users should have at least
> > >  	 * ___GFP_DIRECT_RECLAIM to get here.
> > >  	 */
> > > -	if (oc->gfp_mask && !(oc->gfp_mask & (__GFP_FS|__GFP_NOFAIL)))
> > > +	if (oc->gfp_mask && !(oc->gfp_mask & __GFP_FS))
> > >  		return true;
> > >
> > As to GFP_NOFS|__GFP_NOFAIL request, can we check gfp mask
> > one bit after another?
> >
> > 	if (oc->gfp_mask) {
> > 		if (!(oc->gfp_mask & __GFP_FS))
> > 			return false;
> >
> > 		/* No service for request that can handle fail result itself */
> > 		if (!(oc->gfp_mask & __GFP_NOFAIL))
> > 			return false;
> > 	}
> 
> I really do not understand this request. 

It's a request of both NOFS and NOFAIL, and I think we can keep it from
hitting oom killer by shuffling the current gfp checks.
I hope it can make nit sense to your work.

> This patch is removing the __GFP_NOFAIL part... 

Yes, and I don't stick to handling NOFAIL requests inside oom.
 
> Besides that why should they return false?

It's feedback to page allocator that no kill is issued, and 
extra attention is needed.

thanks
Hillf

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#1566365 — Re: [PATCH 2/3] mm, oom: do not enfore OOM killer for __GFP_NOFAIL automatically

FromMichal Hocko <mhocko@kernel.org>
Date2017-01-25 09:10 +0100
SubjectRe: [PATCH 2/3] mm, oom: do not enfore OOM killer for __GFP_NOFAIL automatically
Message-ID<t3qOt-7Gf-5@gated-at.bofh.it>
In reply to#1566352
On Wed 25-01-17 15:00:51, Hillf Danton wrote:
> On Tuesday, January 24, 2017 8:41 PM Michal Hocko wrote: 
> > On Fri 20-01-17 16:33:36, Hillf Danton wrote:
> > >
> > > On Tuesday, December 20, 2016 9:49 PM Michal Hocko wrote:
> > > >
> > > > @@ -1013,7 +1013,7 @@ bool out_of_memory(struct oom_control *oc)
> > > >  	 * make sure exclude 0 mask - all other users should have at least
> > > >  	 * ___GFP_DIRECT_RECLAIM to get here.
> > > >  	 */
> > > > -	if (oc->gfp_mask && !(oc->gfp_mask & (__GFP_FS|__GFP_NOFAIL)))
> > > > +	if (oc->gfp_mask && !(oc->gfp_mask & __GFP_FS))
> > > >  		return true;
> > > >
> > > As to GFP_NOFS|__GFP_NOFAIL request, can we check gfp mask
> > > one bit after another?
> > >
> > > 	if (oc->gfp_mask) {
> > > 		if (!(oc->gfp_mask & __GFP_FS))
> > > 			return false;
> > >
> > > 		/* No service for request that can handle fail result itself */
> > > 		if (!(oc->gfp_mask & __GFP_NOFAIL))
> > > 			return false;
> > > 	}
> > 
> > I really do not understand this request. 
> 
> It's a request of both NOFS and NOFAIL, and I think we can keep it from
> hitting oom killer by shuffling the current gfp checks.
> I hope it can make nit sense to your work.
> 

I still do not understand. The whole point we are doing the late
__GFP_FS check is explained in 3da88fb3bacf ("mm, oom: move GFP_NOFS
check to out_of_memory"). And the reason why I am _removing_
__GFP_NOFAIL is explained in the changelog of this patch.

> > This patch is removing the __GFP_NOFAIL part... 
> 
> Yes, and I don't stick to handling NOFAIL requests inside oom.
>  
> > Besides that why should they return false?
> 
> It's feedback to page allocator that no kill is issued, and 
> extra attention is needed.

Be careful, the semantic of out_of_memory is different. Returning false
means that the oom killer has been disabled and so the allocation should
fail rather than loop for ever.

-- 
Michal Hocko
SUSE Labs

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#1566391

From"Hillf Danton" <hillf.zj@alibaba-inc.com>
Date2017-01-25 09:50 +0100
Message-ID<t3rrb-7Us-9@gated-at.bofh.it>
In reply to#1566365
On Wednesday, January 25, 2017 4:00 PM Michal Hocko wrote: 
> On Wed 25-01-17 15:00:51, Hillf Danton wrote:
> > On Tuesday, January 24, 2017 8:41 PM Michal Hocko wrote:
> > > On Fri 20-01-17 16:33:36, Hillf Danton wrote:
> > > >
> > > > On Tuesday, December 20, 2016 9:49 PM Michal Hocko wrote:
> > > > >
> > > > > @@ -1013,7 +1013,7 @@ bool out_of_memory(struct oom_control *oc)
> > > > >  	 * make sure exclude 0 mask - all other users should have at least
> > > > >  	 * ___GFP_DIRECT_RECLAIM to get here.
> > > > >  	 */
> > > > > -	if (oc->gfp_mask && !(oc->gfp_mask & (__GFP_FS|__GFP_NOFAIL)))
> > > > > +	if (oc->gfp_mask && !(oc->gfp_mask & __GFP_FS))
> > > > >  		return true;
> > > > >
> > > > As to GFP_NOFS|__GFP_NOFAIL request, can we check gfp mask
> > > > one bit after another?
> > > >
> > > > 	if (oc->gfp_mask) {
> > > > 		if (!(oc->gfp_mask & __GFP_FS))
> > > > 			return false;
> > > >
> > > > 		/* No service for request that can handle fail result itself */
> > > > 		if (!(oc->gfp_mask & __GFP_NOFAIL))
> > > > 			return false;
> > > > 	}
> > >
> > > I really do not understand this request.
> >
> > It's a request of both NOFS and NOFAIL, and I think we can keep it from
> > hitting oom killer by shuffling the current gfp checks.
> > I hope it can make nit sense to your work.
> >
> 
> I still do not understand. The whole point we are doing the late
> __GFP_FS check is explained in 3da88fb3bacf ("mm, oom: move GFP_NOFS
> check to out_of_memory"). And the reason why I am _removing_
> __GFP_NOFAIL is explained in the changelog of this patch.
> 
> > > This patch is removing the __GFP_NOFAIL part...
> >
> > Yes, and I don't stick to handling NOFAIL requests inside oom.
> >
> > > Besides that why should they return false?
> >
> > It's feedback to page allocator that no kill is issued, and
> > extra attention is needed.
> 
> Be careful, the semantic of out_of_memory is different. Returning false
> means that the oom killer has been disabled and so the allocation should
> fail rather than loop for ever.
> 
By returning  false, I mean that oom killer is making no progress.
And I prefer to give up looping if oom killer can't help.
It's a change in the current semantic to fail the request and I have
to test it isn't bad.

thanks
Hillf

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#1566458 — Re: [PATCH 2/3] mm, oom: do not enfore OOM killer for __GFP_NOFAIL automatically

FromMichal Hocko <mhocko@kernel.org>
Date2017-01-25 11:30 +0100
SubjectRe: [PATCH 2/3] mm, oom: do not enfore OOM killer for __GFP_NOFAIL automatically
Message-ID<t3sZY-wo-33@gated-at.bofh.it>
In reply to#1566391
On Wed 25-01-17 16:41:54, Hillf Danton wrote:
> On Wednesday, January 25, 2017 4:00 PM Michal Hocko wrote: 
> > On Wed 25-01-17 15:00:51, Hillf Danton wrote:
> > > On Tuesday, January 24, 2017 8:41 PM Michal Hocko wrote:
> > > > On Fri 20-01-17 16:33:36, Hillf Danton wrote:
> > > > >
> > > > > On Tuesday, December 20, 2016 9:49 PM Michal Hocko wrote:
> > > > > >
> > > > > > @@ -1013,7 +1013,7 @@ bool out_of_memory(struct oom_control *oc)
> > > > > >  	 * make sure exclude 0 mask - all other users should have at least
> > > > > >  	 * ___GFP_DIRECT_RECLAIM to get here.
> > > > > >  	 */
> > > > > > -	if (oc->gfp_mask && !(oc->gfp_mask & (__GFP_FS|__GFP_NOFAIL)))
> > > > > > +	if (oc->gfp_mask && !(oc->gfp_mask & __GFP_FS))
> > > > > >  		return true;
> > > > > >
> > > > > As to GFP_NOFS|__GFP_NOFAIL request, can we check gfp mask
> > > > > one bit after another?
> > > > >
> > > > > 	if (oc->gfp_mask) {
> > > > > 		if (!(oc->gfp_mask & __GFP_FS))
> > > > > 			return false;
> > > > >
> > > > > 		/* No service for request that can handle fail result itself */
> > > > > 		if (!(oc->gfp_mask & __GFP_NOFAIL))
> > > > > 			return false;
> > > > > 	}
> > > >
> > > > I really do not understand this request.
> > >
> > > It's a request of both NOFS and NOFAIL, and I think we can keep it from
> > > hitting oom killer by shuffling the current gfp checks.
> > > I hope it can make nit sense to your work.
> > >
> > 
> > I still do not understand. The whole point we are doing the late
> > __GFP_FS check is explained in 3da88fb3bacf ("mm, oom: move GFP_NOFS
> > check to out_of_memory"). And the reason why I am _removing_
> > __GFP_NOFAIL is explained in the changelog of this patch.
> > 
> > > > This patch is removing the __GFP_NOFAIL part...
> > >
> > > Yes, and I don't stick to handling NOFAIL requests inside oom.
> > >
> > > > Besides that why should they return false?
> > >
> > > It's feedback to page allocator that no kill is issued, and
> > > extra attention is needed.
> > 
> > Be careful, the semantic of out_of_memory is different. Returning false
> > means that the oom killer has been disabled and so the allocation should
> > fail rather than loop for ever.
> > 
> By returning  false, I mean that oom killer is making no progress.
> And I prefer to give up looping if oom killer can't help.
> It's a change in the current semantic to fail the request and I have
> to test it isn't bad.

And it is really off-topic to this particular patch which really
confused me. And no, this wouldn't fly. I have tried that 2 years ago
and failed because the risk of unexpected ENOMEM is just too high.

-- 
Michal Hocko
SUSE Labs

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