Re: [PATCH 1/4] mm/hugetlb: Enable PUD level huge page migration

[Anshuman Khandual <anshuman.khandual@arm.com>]

On 10/03/2018 07:06 PM, Michal Hocko wrote:
> On Wed 03-10-18 18:36:39, Anshuman Khandual wrote:
> [...]
>> So we have two checks here
>>
>> 1) platform specific arch_hugetlb_migration -> In principle go ahead
>>
>> 2) huge_movable() during allocation
>>
>> 	- If huge page does not have to be placed on movable zone
>>
>> 		- Allocate any where successfully and done !
>>  
>> 	- If huge page *should* be placed on a movable zone
>>
>> 		- Try allocating on movable zone
>>
>> 			- Successfull and done !
>>
>> 		- If the new page could not be allocated on movable zone
>> 		
>> 			- Abort the migration completely
>>
>> 					OR
>>
>> 			- Warn and fall back to non-movable
> 
> I guess you are still making it more complicated than necessary. The
> later is really only about __GFP_MOVABLE at this stage. I would just
> make it simple for now. We do not have to implement any dynamic
> heuristic right now. All that I am asking for is to split the migrate
> possible part from movable part.
> 
> I should have been more clear about that I guess from my very first
> reply. I do like how you moved the current coarse grained
> hugepage_migration_supported to be more arch specific but I merely
> wanted to point out that we need to do some other changes before we can
> go that route and that thing is to distinguish movable from migration
> supported.
> 
> See my point?

Does the following sound close enough to what you are looking for ?

diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index 9df1d59..070c419 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -504,6 +504,13 @@ static inline bool hugepage_migration_supported(struct hstate *h)
        return arch_hugetlb_migration_supported(h);
 }
 
+static inline bool hugepage_movable_required(struct hstate *h)
+{
+       if (hstate_is_gigantic(h))
+               return true;
+       return false;
+}
+
 static inline spinlock_t *huge_pte_lockptr(struct hstate *h,
                                           struct mm_struct *mm, pte_t *pte)
 {
@@ -600,6 +607,11 @@ static inline bool hugepage_migration_supported(struct hstate *h)
        return false;
 }
 
+static inline bool hugepage_movable_required(struct hstate *h)
+{
+       return false;
+}
+
 static inline spinlock_t *huge_pte_lockptr(struct hstate *h,
                                           struct mm_struct *mm, pte_t *pte)
 {
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 3c21775..8b0afdc 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1635,6 +1635,9 @@ struct page *alloc_huge_page_node(struct hstate *h, int nid)
        if (nid != NUMA_NO_NODE)
                gfp_mask |= __GFP_THISNODE;
 
+       if (hugepage_movable_required(h))
+               gfp_mask |= __GFP_MOVABLE;
+
        spin_lock(&hugetlb_lock);
        if (h->free_huge_pages - h->resv_huge_pages > 0)
                page = dequeue_huge_page_nodemask(h, gfp_mask, nid, NULL);
@@ -1652,6 +1655,9 @@ struct page *alloc_huge_page_nodemask(struct hstate *h, int preferred_nid,
 {
        gfp_t gfp_mask = htlb_alloc_mask(h);
 
+       if (hugepage_movable_required(h))
+               gfp_mask |= __GFP_MOVABLE;
+
        spin_lock(&hugetlb_lock);
        if (h->free_huge_pages - h->resv_huge_pages > 0) {
                struct page *page;