Re: [patch v2 for-4.0] mm, thp: really limit transparent hugepage allocation to local node
Vlastimil Babka writes: > On 04/21/2015 09:31 AM, Aneesh Kumar K.V wrote: >> Vlastimil Babka writes: >> >>> On 25.2.2015 22:24, David Rientjes wrote: > alloc_pages_preferred_node() variant, change the exact_node() variant to > pass > __GFP_THISNODE, and audit and adjust all callers accordingly. > ... >>> Right, we might be changing behavior not just for slab allocators, but >>> also others using such >>> combination of flags. >> >> Any update on this ? Did we reach a conclusion on how to go forward here >> ? > > I believe David's later version was merged already. Or what exactly are > you asking about? When I checked last time I didn't find it. Hence I asked here. Now I see that it got committed as 5265047ac30191ea24b16503165000c225f54feb Thanks -aneesh -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [patch v2 for-4.0] mm, thp: really limit transparent hugepage allocation to local node
On 04/21/2015 09:31 AM, Aneesh Kumar K.V wrote: Vlastimil Babka writes: On 25.2.2015 22:24, David Rientjes wrote: alloc_pages_preferred_node() variant, change the exact_node() variant to pass __GFP_THISNODE, and audit and adjust all callers accordingly. Sounds like that should be done as part of a cleanup after the 4.0 issues are addressed. alloc_pages_exact_node() does seem to suggest that we want exactly that node, implying __GFP_THISNODE behavior already, so it would be good to avoid having this come up again in the future. Oh lovely, just found out that there's alloc_pages_node which should be the preferred-only version, but in fact does not differ from alloc_pages_exact_node in any relevant way. I agree we should do some larger cleanup for next version. Also, you pass __GFP_NOWARN but that should be covered by GFP_TRANSHUGE already. Of course, nothing guarantees that hugepage == true implies that gfp == GFP_TRANSHUGE... but current in-tree callers conform to that. Ah, good point, and it includes __GFP_NORETRY as well which means that this patch is busted. It won't try compaction or direct reclaim in the page allocator slowpath because of this: /* * GFP_THISNODE (meaning __GFP_THISNODE, __GFP_NORETRY and * __GFP_NOWARN set) should not cause reclaim since the subsystem * (f.e. slab) using GFP_THISNODE may choose to trigger reclaim * using a larger set of nodes after it has established that the * allowed per node queues are empty and that nodes are * over allocated. */ if (IS_ENABLED(CONFIG_NUMA) && (gfp_mask & GFP_THISNODE) == GFP_THISNODE) goto nopage; Hmm. It would be disappointing to have to pass the nodemask of the exact node that we want to allocate from into the page allocator to avoid using __GFP_THISNODE. Yeah. There's a sneaky way around it by just removing __GFP_NORETRY from GFP_TRANSHUGE so the condition above fails and since the page allocator won't retry for such a high-order allocation, but that probably just papers over this stuff too much already. I think what we want to do is Alternatively alloc_pages_exact_node() adds __GFP_THISNODE just to node_zonelist() call and not to __alloc_pages() gfp_mask proper? Unless __GFP_THISNODE was given *also* in the incoming gfp_mask, this should give us the right combination? But it's also subtle cause the slab allocators to not use __GFP_WAIT if they want to avoid reclaim. Yes, the fewer subtle heuristics we have that include combinations of flags (*cough* GFP_TRANSHUGE *cough*), the better. This is probably going to be a much more invasive patch than originally thought. Right, we might be changing behavior not just for slab allocators, but also others using such combination of flags. Any update on this ? Did we reach a conclusion on how to go forward here ? I believe David's later version was merged already. Or what exactly are you asking about? -aneesh -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [patch v2 for-4.0] mm, thp: really limit transparent hugepage allocation to local node
Vlastimil Babka writes: > On 25.2.2015 22:24, David Rientjes wrote: >> >>> alloc_pages_preferred_node() variant, change the exact_node() variant to >>> pass >>> __GFP_THISNODE, and audit and adjust all callers accordingly. >>> >> Sounds like that should be done as part of a cleanup after the 4.0 issues >> are addressed. alloc_pages_exact_node() does seem to suggest that we want >> exactly that node, implying __GFP_THISNODE behavior already, so it would >> be good to avoid having this come up again in the future. > > Oh lovely, just found out that there's alloc_pages_node which should be the > preferred-only version, but in fact does not differ from > alloc_pages_exact_node > in any relevant way. I agree we should do some larger cleanup for next > version. > >>> Also, you pass __GFP_NOWARN but that should be covered by GFP_TRANSHUGE >>> already. Of course, nothing guarantees that hugepage == true implies that >>> gfp >>> == GFP_TRANSHUGE... but current in-tree callers conform to that. >>> >> Ah, good point, and it includes __GFP_NORETRY as well which means that >> this patch is busted. It won't try compaction or direct reclaim in the >> page allocator slowpath because of this: >> >> /* >> * GFP_THISNODE (meaning __GFP_THISNODE, __GFP_NORETRY and >> * __GFP_NOWARN set) should not cause reclaim since the subsystem >> * (f.e. slab) using GFP_THISNODE may choose to trigger reclaim >> * using a larger set of nodes after it has established that the >> * allowed per node queues are empty and that nodes are >> * over allocated. >> */ >> if (IS_ENABLED(CONFIG_NUMA) && >> (gfp_mask & GFP_THISNODE) == GFP_THISNODE) >> goto nopage; >> >> Hmm. It would be disappointing to have to pass the nodemask of the exact >> node that we want to allocate from into the page allocator to avoid using >> __GFP_THISNODE. > > Yeah. > >> >> There's a sneaky way around it by just removing __GFP_NORETRY from >> GFP_TRANSHUGE so the condition above fails and since the page allocator >> won't retry for such a high-order allocation, but that probably just >> papers over this stuff too much already. I think what we want to do is > > Alternatively alloc_pages_exact_node() adds __GFP_THISNODE just to > node_zonelist() call and not to __alloc_pages() gfp_mask proper? Unless > __GFP_THISNODE > was given *also* in the incoming gfp_mask, this should give us the right > combination? > But it's also subtle > >> cause the slab allocators to not use __GFP_WAIT if they want to avoid >> reclaim. > > Yes, the fewer subtle heuristics we have that include combinations of > flags (*cough* > GFP_TRANSHUGE *cough*), the better. > >> This is probably going to be a much more invasive patch than originally >> thought. > > Right, we might be changing behavior not just for slab allocators, but > also others using such > combination of flags. Any update on this ? Did we reach a conclusion on how to go forward here ? -aneesh -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [patch v2 for-4.0] mm, thp: really limit transparent hugepage allocation to local node
On 25.2.2015 22:24, David Rientjes wrote: alloc_pages_preferred_node() variant, change the exact_node() variant to pass __GFP_THISNODE, and audit and adjust all callers accordingly. Sounds like that should be done as part of a cleanup after the 4.0 issues are addressed. alloc_pages_exact_node() does seem to suggest that we want exactly that node, implying __GFP_THISNODE behavior already, so it would be good to avoid having this come up again in the future. Oh lovely, just found out that there's alloc_pages_node which should be the preferred-only version, but in fact does not differ from alloc_pages_exact_node in any relevant way. I agree we should do some larger cleanup for next version. Also, you pass __GFP_NOWARN but that should be covered by GFP_TRANSHUGE already. Of course, nothing guarantees that hugepage == true implies that gfp == GFP_TRANSHUGE... but current in-tree callers conform to that. Ah, good point, and it includes __GFP_NORETRY as well which means that this patch is busted. It won't try compaction or direct reclaim in the page allocator slowpath because of this: /* * GFP_THISNODE (meaning __GFP_THISNODE, __GFP_NORETRY and * __GFP_NOWARN set) should not cause reclaim since the subsystem * (f.e. slab) using GFP_THISNODE may choose to trigger reclaim * using a larger set of nodes after it has established that the * allowed per node queues are empty and that nodes are * over allocated. */ if (IS_ENABLED(CONFIG_NUMA) && (gfp_mask & GFP_THISNODE) == GFP_THISNODE) goto nopage; Hmm. It would be disappointing to have to pass the nodemask of the exact node that we want to allocate from into the page allocator to avoid using __GFP_THISNODE. Yeah. There's a sneaky way around it by just removing __GFP_NORETRY from GFP_TRANSHUGE so the condition above fails and since the page allocator won't retry for such a high-order allocation, but that probably just papers over this stuff too much already. I think what we want to do is Alternatively alloc_pages_exact_node() adds __GFP_THISNODE just to node_zonelist() call and not to __alloc_pages() gfp_mask proper? Unless __GFP_THISNODE was given *also* in the incoming gfp_mask, this should give us the right combination? But it's also subtle cause the slab allocators to not use __GFP_WAIT if they want to avoid reclaim. Yes, the fewer subtle heuristics we have that include combinations of flags (*cough* GFP_TRANSHUGE *cough*), the better. This is probably going to be a much more invasive patch than originally thought. Right, we might be changing behavior not just for slab allocators, but also others using such combination of flags. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [patch v2 for-4.0] mm, thp: really limit transparent hugepage allocation to local node
On Wed, 25 Feb 2015, Vlastimil Babka wrote:
> > Commit 077fcf116c8c ("mm/thp: allocate transparent hugepages on local
> > node") restructured alloc_hugepage_vma() with the intent of only
> > allocating transparent hugepages locally when there was not an effective
> > interleave mempolicy.
> >
> > alloc_pages_exact_node() does not limit the allocation to the single
> > node, however, but rather prefers it. This is because __GFP_THISNODE is
> > not set which would cause the node-local nodemask to be passed. Without
> > it, only a nodemask that prefers the local node is passed.
>
> Oops, good catch.
> But I believe we have the same problem with khugepaged_alloc_page(), rendering
> the recent node determination and zone_reclaim strictness patches partially
> useless.
>
Indeed.
> Then I start to wonder about other alloc_pages_exact_node() users. Some do
> pass __GFP_THISNODE, others not - are they also mistaken? I guess the function
> is a misnomer - when I see "exact_node", I expect the __GFP_THISNODE behavior.
>
I looked through these yesterday as well and could only find the
do_migrate_pages() case for page migration where __GFP_THISNODE was
missing. I proposed that separately as
http://marc.info/?l=linux-mm&m=142481989722497 -- I couldn't find any
other users that looked wrong.
> I think to avoid such hidden catches, we should create
> alloc_pages_preferred_node() variant, change the exact_node() variant to pass
> __GFP_THISNODE, and audit and adjust all callers accordingly.
>
Sounds like that should be done as part of a cleanup after the 4.0 issues
are addressed. alloc_pages_exact_node() does seem to suggest that we want
exactly that node, implying __GFP_THISNODE behavior already, so it would
be good to avoid having this come up again in the future.
> Also, you pass __GFP_NOWARN but that should be covered by GFP_TRANSHUGE
> already. Of course, nothing guarantees that hugepage == true implies that gfp
> == GFP_TRANSHUGE... but current in-tree callers conform to that.
>
Ah, good point, and it includes __GFP_NORETRY as well which means that
this patch is busted. It won't try compaction or direct reclaim in the
page allocator slowpath because of this:
/*
* GFP_THISNODE (meaning __GFP_THISNODE, __GFP_NORETRY and
* __GFP_NOWARN set) should not cause reclaim since the subsystem
* (f.e. slab) using GFP_THISNODE may choose to trigger reclaim
* using a larger set of nodes after it has established that the
* allowed per node queues are empty and that nodes are
* over allocated.
*/
if (IS_ENABLED(CONFIG_NUMA) &&
(gfp_mask & GFP_THISNODE) == GFP_THISNODE)
goto nopage;
Hmm. It would be disappointing to have to pass the nodemask of the exact
node that we want to allocate from into the page allocator to avoid using
__GFP_THISNODE.
There's a sneaky way around it by just removing __GFP_NORETRY from
GFP_TRANSHUGE so the condition above fails and since the page allocator
won't retry for such a high-order allocation, but that probably just
papers over this stuff too much already. I think what we want to do is
cause the slab allocators to not use __GFP_WAIT if they want to avoid
reclaim.
This is probably going to be a much more invasive patch than originally
thought.
--
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the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
Re: [patch v2 for-4.0] mm, thp: really limit transparent hugepage allocation to local node
On 02/25/2015 12:24 AM, David Rientjes wrote:
From: Greg Thelen
Commit 077fcf116c8c ("mm/thp: allocate transparent hugepages on local
node") restructured alloc_hugepage_vma() with the intent of only
allocating transparent hugepages locally when there was not an effective
interleave mempolicy.
alloc_pages_exact_node() does not limit the allocation to the single
node, however, but rather prefers it. This is because __GFP_THISNODE is
not set which would cause the node-local nodemask to be passed. Without
it, only a nodemask that prefers the local node is passed.
Oops, good catch.
But I believe we have the same problem with khugepaged_alloc_page(),
rendering the recent node determination and zone_reclaim strictness
patches partially useless.
Then I start to wonder about other alloc_pages_exact_node() users. Some
do pass __GFP_THISNODE, others not - are they also mistaken? I guess the
function is a misnomer - when I see "exact_node", I expect the
__GFP_THISNODE behavior.
I think to avoid such hidden catches, we should create
alloc_pages_preferred_node() variant, change the exact_node() variant to
pass __GFP_THISNODE, and audit and adjust all callers accordingly.
Also, you pass __GFP_NOWARN but that should be covered by GFP_TRANSHUGE
already. Of course, nothing guarantees that hugepage == true implies
that gfp == GFP_TRANSHUGE... but current in-tree callers conform to that.
Fix this by passing __GFP_THISNODE and falling back to small pages when
the allocation fails.
Fixes: 077fcf116c8c ("mm/thp: allocate transparent hugepages on local node")
Signed-off-by: Greg Thelen
Signed-off-by: David Rientjes
---
v2: GFP_THISNODE actually defers compaction and reclaim entirely based on
the combination of gfp flags. We want to try compaction and reclaim,
so only set __GFP_THISNODE. We still set __GFP_NOWARN to suppress
oom warnings in the kernel log when we can simply fallback to small
pages.
mm/mempolicy.c | 5 -
1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -1985,7 +1985,10 @@ retry_cpuset:
nmask = policy_nodemask(gfp, pol);
if (!nmask || node_isset(node, *nmask)) {
mpol_cond_put(pol);
- page = alloc_pages_exact_node(node, gfp, order);
+ page = alloc_pages_exact_node(node, gfp |
+ __GFP_THISNODE |
+ __GFP_NOWARN,
+ order);
goto out;
}
}
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