* [PATCH] mm,memory_hotplug: Explicitly pass the head to isolate_huge_page
@ 2019-02-08 9:06 Oscar Salvador
2019-02-11 8:58 ` David Hildenbrand
2019-02-12 8:33 ` Michal Hocko
0 siblings, 2 replies; 9+ messages in thread
From: Oscar Salvador @ 2019-02-08 9:06 UTC (permalink / raw)
To: akpm
Cc: mhocko, david, anthony.yznaga, linux-mm, linux-kernel, Oscar Salvador
isolate_huge_page() expects we pass the head of hugetlb page to it:
bool isolate_huge_page(...)
{
...
VM_BUG_ON_PAGE(!PageHead(page), page);
...
}
While I really cannot think of any situation where we end up with a
non-head page between hands in do_migrate_range(), let us make sure
the code is as sane as possible by explicitly passing the Head.
Since we already got the pointer, it does not take us extra effort.
Signed-off-by: Oscar Salvador <osalvador@suse.de>
---
mm/memory_hotplug.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 656ff386ac15..d5f7afda67db 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1378,12 +1378,12 @@ do_migrate_range(unsigned long start_pfn, unsigned long end_pfn)
if (PageHuge(page)) {
struct page *head = compound_head(page);
- pfn = page_to_pfn(head) + (1<<compound_order(head)) - 1;
if (compound_order(head) > PFN_SECTION_SHIFT) {
ret = -EBUSY;
break;
}
- isolate_huge_page(page, &source);
+ pfn = page_to_pfn(head) + (1<<compound_order(head)) - 1;
+ isolate_huge_page(head, &source);
continue;
} else if (PageTransHuge(page))
pfn = page_to_pfn(compound_head(page))
--
2.13.7
^ permalink raw reply related [flat|nested] 9+ messages in thread
* Re: [PATCH] mm,memory_hotplug: Explicitly pass the head to isolate_huge_page
2019-02-08 9:06 [PATCH] mm,memory_hotplug: Explicitly pass the head to isolate_huge_page Oscar Salvador
@ 2019-02-11 8:58 ` David Hildenbrand
2019-02-12 8:33 ` Michal Hocko
1 sibling, 0 replies; 9+ messages in thread
From: David Hildenbrand @ 2019-02-11 8:58 UTC (permalink / raw)
To: Oscar Salvador, akpm; +Cc: mhocko, anthony.yznaga, linux-mm, linux-kernel
On 08.02.19 10:06, Oscar Salvador wrote:
> isolate_huge_page() expects we pass the head of hugetlb page to it:
>
> bool isolate_huge_page(...)
> {
> ...
> VM_BUG_ON_PAGE(!PageHead(page), page);
> ...
> }
>
> While I really cannot think of any situation where we end up with a
> non-head page between hands in do_migrate_range(), let us make sure
> the code is as sane as possible by explicitly passing the Head.
> Since we already got the pointer, it does not take us extra effort.
>
> Signed-off-by: Oscar Salvador <osalvador@suse.de>
> ---
> mm/memory_hotplug.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 656ff386ac15..d5f7afda67db 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1378,12 +1378,12 @@ do_migrate_range(unsigned long start_pfn, unsigned long end_pfn)
>
> if (PageHuge(page)) {
> struct page *head = compound_head(page);
> - pfn = page_to_pfn(head) + (1<<compound_order(head)) - 1;
> if (compound_order(head) > PFN_SECTION_SHIFT) {
> ret = -EBUSY;
> break;
> }
> - isolate_huge_page(page, &source);
> + pfn = page_to_pfn(head) + (1<<compound_order(head)) - 1;
> + isolate_huge_page(head, &source);
> continue;
> } else if (PageTransHuge(page))
> pfn = page_to_pfn(compound_head(page))
>
Reviewed-by: David Hildenbrand <david@redhat.com>
--
Thanks,
David / dhildenb
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH] mm,memory_hotplug: Explicitly pass the head to isolate_huge_page
2019-02-08 9:06 [PATCH] mm,memory_hotplug: Explicitly pass the head to isolate_huge_page Oscar Salvador
2019-02-11 8:58 ` David Hildenbrand
@ 2019-02-12 8:33 ` Michal Hocko
2019-02-12 13:45 ` Oscar Salvador
1 sibling, 1 reply; 9+ messages in thread
From: Michal Hocko @ 2019-02-12 8:33 UTC (permalink / raw)
To: Oscar Salvador; +Cc: akpm, david, anthony.yznaga, linux-mm, linux-kernel
On Fri 08-02-19 10:06:04, Oscar Salvador wrote:
> isolate_huge_page() expects we pass the head of hugetlb page to it:
>
> bool isolate_huge_page(...)
> {
> ...
> VM_BUG_ON_PAGE(!PageHead(page), page);
> ...
> }
>
> While I really cannot think of any situation where we end up with a
> non-head page between hands in do_migrate_range(), let us make sure
> the code is as sane as possible by explicitly passing the Head.
> Since we already got the pointer, it does not take us extra effort.
>
> Signed-off-by: Oscar Salvador <osalvador@suse.de>
Acked-by: Michal Hocko <mhocko@suse.com>
Btw.
> ---
> mm/memory_hotplug.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 656ff386ac15..d5f7afda67db 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1378,12 +1378,12 @@ do_migrate_range(unsigned long start_pfn, unsigned long end_pfn)
>
> if (PageHuge(page)) {
> struct page *head = compound_head(page);
> - pfn = page_to_pfn(head) + (1<<compound_order(head)) - 1;
> if (compound_order(head) > PFN_SECTION_SHIFT) {
> ret = -EBUSY;
> break;
> }
Why are we doing this, btw?
> - isolate_huge_page(page, &source);
> + pfn = page_to_pfn(head) + (1<<compound_order(head)) - 1;
> + isolate_huge_page(head, &source);
> continue;
> } else if (PageTransHuge(page))
> pfn = page_to_pfn(compound_head(page))
> --
> 2.13.7
--
Michal Hocko
SUSE Labs
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH] mm,memory_hotplug: Explicitly pass the head to isolate_huge_page
2019-02-12 8:33 ` Michal Hocko
@ 2019-02-12 13:45 ` Oscar Salvador
2019-02-12 14:40 ` Michal Hocko
0 siblings, 1 reply; 9+ messages in thread
From: Oscar Salvador @ 2019-02-12 13:45 UTC (permalink / raw)
To: Michal Hocko; +Cc: akpm, david, anthony.yznaga, linux-mm, linux-kernel
On Tue, Feb 12, 2019 at 09:33:29AM +0100, Michal Hocko wrote:
> >
> > if (PageHuge(page)) {
> > struct page *head = compound_head(page);
> > - pfn = page_to_pfn(head) + (1<<compound_order(head)) - 1;
> > if (compound_order(head) > PFN_SECTION_SHIFT) {
> > ret = -EBUSY;
> > break;
> > }
>
> Why are we doing this, btw?
I assume you are referring to:
> > if (compound_order(head) > PFN_SECTION_SHIFT) {
> > ret = -EBUSY;
> > break;
> > }
I thought it was in case we stumble upon a gigantic page, and commit
(c8721bbbdd36 mm: memory-hotplug: enable memory hotplug to handle hugepage)
confirms it.
But I am not really sure if the above condition would still hold on powerpc,
I wanted to check it but it is a bit more tricky than it is in x86_64 because
of the different hugetlb sizes.
Could it be that the above condition is not true, but still the order of that
hugetlb page goes beyond MAX_ORDER? It is something I have to check.
Anyway, I think that a safer way to check this would be using hstate_is_gigantic(),
which checks whether the order of the hstate goes beyond MAX_ORDER.
In the end, I think that all we care about is if we can get the pages to migrate
to via the buddy allocator, since gigantic pages need to use another method.
Actually, alloc_migrate_huge_page() checks for it:
<---
static struct page *alloc_migrate_huge_page(struct hstate *h, gfp_t gfp_mask,
int nid, nodemask_t *nmask)
{
if (hstate_is_gigantic(h))
return NULL;
--->
Another thing is that AFAICS, as long as the memblock we try to offline contains
a gigantic page, it will not be able to be offlined.
Moreover, the -EBUSY we return in that case is not checked anywhere, although that
is not really an issue because scan_movable_pages will skip it in the next loop.
Now, this is more rambling than anything:
Maybe I am missing half of the picture, but I have been thinking for a while whether
we could do better when it comes to gigantic pages vs hotplug.
I think that we could try to migrate those in case any of the other nodes
have a spare pre-allocated gigantic page.
--
Oscar Salvador
SUSE L3
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH] mm,memory_hotplug: Explicitly pass the head to isolate_huge_page
2019-02-12 13:45 ` Oscar Salvador
@ 2019-02-12 14:40 ` Michal Hocko
2019-02-13 0:13 ` Mike Kravetz
0 siblings, 1 reply; 9+ messages in thread
From: Michal Hocko @ 2019-02-12 14:40 UTC (permalink / raw)
To: Oscar Salvador; +Cc: akpm, david, anthony.yznaga, linux-mm, linux-kernel
On Tue 12-02-19 14:45:49, Oscar Salvador wrote:
> On Tue, Feb 12, 2019 at 09:33:29AM +0100, Michal Hocko wrote:
> > >
> > > if (PageHuge(page)) {
> > > struct page *head = compound_head(page);
> > > - pfn = page_to_pfn(head) + (1<<compound_order(head)) - 1;
> > > if (compound_order(head) > PFN_SECTION_SHIFT) {
> > > ret = -EBUSY;
> > > break;
> > > }
> >
> > Why are we doing this, btw?
>
> I assume you are referring to:
>
> > > if (compound_order(head) > PFN_SECTION_SHIFT) {
> > > ret = -EBUSY;
> > > break;
> > > }
yes.
> I thought it was in case we stumble upon a gigantic page, and commit
> (c8721bbbdd36 mm: memory-hotplug: enable memory hotplug to handle hugepage)
> confirms it.
>
> But I am not really sure if the above condition would still hold on powerpc,
> I wanted to check it but it is a bit more tricky than it is in x86_64 because
> of the different hugetlb sizes.
> Could it be that the above condition is not true, but still the order of that
> hugetlb page goes beyond MAX_ORDER? It is something I have to check.
This check doesn't make much sense in principle. Why should we bail out
based on a section size? We are offlining a pfn range. All that we care
about is whether the hugetlb is migrateable.
--
Michal Hocko
SUSE Labs
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH] mm,memory_hotplug: Explicitly pass the head to isolate_huge_page
2019-02-12 14:40 ` Michal Hocko
@ 2019-02-13 0:13 ` Mike Kravetz
2019-02-13 8:13 ` Oscar Salvador
0 siblings, 1 reply; 9+ messages in thread
From: Mike Kravetz @ 2019-02-13 0:13 UTC (permalink / raw)
To: Michal Hocko, Oscar Salvador
Cc: akpm, david, anthony.yznaga, linux-mm, linux-kernel
On 2/12/19 6:40 AM, Michal Hocko wrote:
> On Tue 12-02-19 14:45:49, Oscar Salvador wrote:
>> On Tue, Feb 12, 2019 at 09:33:29AM +0100, Michal Hocko wrote:
>>>>
>>>> if (PageHuge(page)) {
>>>> struct page *head = compound_head(page);
>>>> - pfn = page_to_pfn(head) + (1<<compound_order(head)) - 1;
>>>> if (compound_order(head) > PFN_SECTION_SHIFT) {
>>>> ret = -EBUSY;
>>>> break;
>>>> }
>>>
>>> Why are we doing this, btw?
>>
>> I assume you are referring to:
>>
>>>> if (compound_order(head) > PFN_SECTION_SHIFT) {
>>>> ret = -EBUSY;
>>>> break;
>>>> }
>
> yes.
>
>> I thought it was in case we stumble upon a gigantic page, and commit
>> (c8721bbbdd36 mm: memory-hotplug: enable memory hotplug to handle hugepage)
>> confirms it.
>>
>> But I am not really sure if the above condition would still hold on powerpc,
>> I wanted to check it but it is a bit more tricky than it is in x86_64 because
>> of the different hugetlb sizes.
>> Could it be that the above condition is not true, but still the order of that
>> hugetlb page goes beyond MAX_ORDER? It is something I have to check.
Well, commit 94310cbcaa3c ("mm/madvise: enable (soft|hard) offline of
HugeTLB pages at PGD level") should have allowed migration of gigantic
pages. I believe it was added for 16GB pages on powerpc. However, due
to subsequent changes I suspsect this no longer works.
> This check doesn't make much sense in principle. Why should we bail out
> based on a section size? We are offlining a pfn range. All that we care
> about is whether the hugetlb is migrateable.
Yes. Do note that the do_migrate_range is only called from __offline_pages
with a start_pfn that was returned by scan_movable_pages. scan_movable_pages
has the hugepage_migration_supported check for PageHuge pages. So, it would
seem to be redundant to do another check in do_migrate_range.
--
Mike Kravetz
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH] mm,memory_hotplug: Explicitly pass the head to isolate_huge_page
2019-02-13 0:13 ` Mike Kravetz
@ 2019-02-13 8:13 ` Oscar Salvador
2019-02-13 12:33 ` Michal Hocko
0 siblings, 1 reply; 9+ messages in thread
From: Oscar Salvador @ 2019-02-13 8:13 UTC (permalink / raw)
To: Mike Kravetz
Cc: Michal Hocko, akpm, david, anthony.yznaga, linux-mm, linux-kernel
On Tue, Feb 12, 2019 at 04:13:05PM -0800, Mike Kravetz wrote:
> Well, commit 94310cbcaa3c ("mm/madvise: enable (soft|hard) offline of
> HugeTLB pages at PGD level") should have allowed migration of gigantic
> pages. I believe it was added for 16GB pages on powerpc. However, due
> to subsequent changes I suspsect this no longer works.
I will take a look, I am definitely interested in that.
Thanks for pointing it out Mike.
>
> > This check doesn't make much sense in principle. Why should we bail out
> > based on a section size? We are offlining a pfn range. All that we care
> > about is whether the hugetlb is migrateable.
>
> Yes. Do note that the do_migrate_range is only called from __offline_pages
> with a start_pfn that was returned by scan_movable_pages. scan_movable_pages
> has the hugepage_migration_supported check for PageHuge pages. So, it would
> seem to be redundant to do another check in do_migrate_range.
Well, the thing is that if the gigantic page does not start at the very beginning
of the memblock, and we do find migrateable pages before it in scan_movable_pages(),
the range that we will pass to do_migrate_ranges() will contain the gigantic page.
So we need the check there to cover that case too, although I agree that the current
check is misleading.
I will think about it.
--
Oscar Salvador
SUSE L3
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH] mm,memory_hotplug: Explicitly pass the head to isolate_huge_page
2019-02-13 8:13 ` Oscar Salvador
@ 2019-02-13 12:33 ` Michal Hocko
2019-02-13 15:15 ` Oscar Salvador
0 siblings, 1 reply; 9+ messages in thread
From: Michal Hocko @ 2019-02-13 12:33 UTC (permalink / raw)
To: Oscar Salvador
Cc: Mike Kravetz, akpm, david, anthony.yznaga, linux-mm, linux-kernel
On Wed 13-02-19 09:13:14, Oscar Salvador wrote:
> On Tue, Feb 12, 2019 at 04:13:05PM -0800, Mike Kravetz wrote:
> > Well, commit 94310cbcaa3c ("mm/madvise: enable (soft|hard) offline of
> > HugeTLB pages at PGD level") should have allowed migration of gigantic
> > pages. I believe it was added for 16GB pages on powerpc. However, due
> > to subsequent changes I suspsect this no longer works.
>
> I will take a look, I am definitely interested in that.
> Thanks for pointing it out Mike.
>
> >
> > > This check doesn't make much sense in principle. Why should we bail out
> > > based on a section size? We are offlining a pfn range. All that we care
> > > about is whether the hugetlb is migrateable.
> >
> > Yes. Do note that the do_migrate_range is only called from __offline_pages
> > with a start_pfn that was returned by scan_movable_pages. scan_movable_pages
> > has the hugepage_migration_supported check for PageHuge pages. So, it would
> > seem to be redundant to do another check in do_migrate_range.
>
> Well, the thing is that if the gigantic page does not start at the very beginning
> of the memblock, and we do find migrateable pages before it in scan_movable_pages(),
> the range that we will pass to do_migrate_ranges() will contain the gigantic page.
> So we need the check there to cover that case too, although I agree that the current
> check is misleading.
Why isn't our check in has_unmovable_pages sufficient?
--
Michal Hocko
SUSE Labs
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH] mm,memory_hotplug: Explicitly pass the head to isolate_huge_page
2019-02-13 12:33 ` Michal Hocko
@ 2019-02-13 15:15 ` Oscar Salvador
0 siblings, 0 replies; 9+ messages in thread
From: Oscar Salvador @ 2019-02-13 15:15 UTC (permalink / raw)
To: Michal Hocko
Cc: Mike Kravetz, akpm, david, anthony.yznaga, linux-mm, linux-kernel
On Wed, Feb 13, 2019 at 01:33:39PM +0100, Michal Hocko wrote:
> Why isn't our check in has_unmovable_pages sufficient?
Taking a closer look, it should be enough.
I was mainly confused by the fact that if the zone is ZONE_MOVABLE,
we do not keep checking in has_unmovable_pages():
if (zone_idx(zone) == ZONE_MOVABLE)
continue;
But I overlooked that htlb_alloc_mask() checks whether the allocation
cand end up in a movable zone.
hugepage_movable_supported() checks that and if the hstate does not
support migration at all, we skip __GFP_MOVABLE.
So I think that the check in has_unmovable_pages() should be more than enough,
so we could strip the checks from do_migrate_ranges() and
scan_movable_pages() regarding hugepage migratability.
I will run some tests just to make sure this holds and then
I will send a patch.
Thanks
--
Oscar Salvador
SUSE L3
^ permalink raw reply [flat|nested] 9+ messages in thread
end of thread, other threads:[~2019-02-13 15:15 UTC | newest]
Thread overview: 9+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2019-02-08 9:06 [PATCH] mm,memory_hotplug: Explicitly pass the head to isolate_huge_page Oscar Salvador
2019-02-11 8:58 ` David Hildenbrand
2019-02-12 8:33 ` Michal Hocko
2019-02-12 13:45 ` Oscar Salvador
2019-02-12 14:40 ` Michal Hocko
2019-02-13 0:13 ` Mike Kravetz
2019-02-13 8:13 ` Oscar Salvador
2019-02-13 12:33 ` Michal Hocko
2019-02-13 15:15 ` Oscar Salvador
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