On Mon, Mar 18, 2013 at 05:07:37PM +0100, Michal Hocko wrote:
> On Thu 21-02-13 14:41:47, Naoya Horiguchi wrote:
> > Currently we can't offline memory blocks which contain hugepages because
> > a hugepage is considered as an unmovable page. But now with this patch
> > series, a hugepage has become movable, so by using hugepage migration we
> > can offline such memory blocks.
> >
> > What's different from other users of hugepage migration is that we need
> > to decompose all the hugepages inside the target memory block into free
> > buddy pages after hugepage migration, because otherwise free hugepages
> > remaining in the memory block intervene the memory offlining.
> > For this reason we introduce new functions dissolve_free_huge_page() and
> > dissolve_free_huge_pages().
> >
> > Other than that, what this patch does is straightforwardly to add hugepage
> > migration code, that is, adding hugepage code to the functions which scan
> > over pfn and collect hugepages to be migrated, and adding a hugepage
> > allocation function to alloc_migrate_target().
> >
> > As for larger hugepages (1GB for x86_64), it's not easy to do hotremove
> > over them because it's larger than memory block. So we now simply leave
> > it to fail as it is.
>
> What we could do is to check whether there is a free gb huge page on
> other node and migrate there.
Correct, and 1GB page migration needs more code in migration core code
(mainly it's related to migration entry in pud) and enough testing,
so I want to do it in separate patchset.
> > Signed-off-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
> > ---
> > include/linux/hugetlb.h | 8 ++++++++
> > mm/hugetlb.c | 43 +++++++++++++++++++++++++++++++++++++++++
> > mm/memory_hotplug.c | 51 ++++++++++++++++++++++++++++++++++++++++---------
> > mm/migrate.c | 12 +++++++++++-
> > mm/page_alloc.c | 12 ++++++++++++
> > mm/page_isolation.c | 5 +++++
> > 6 files changed, 121 insertions(+), 10 deletions(-)
> >
> > diff --git v3.8.orig/include/linux/hugetlb.h v3.8/include/linux/hugetlb.h
> > index 86a4d78..e33f07f 100644
> > --- v3.8.orig/include/linux/hugetlb.h
> > +++ v3.8/include/linux/hugetlb.h
> > @@ -70,6 +70,7 @@ int dequeue_hwpoisoned_huge_page(struct page *page);
> > void putback_active_hugepage(struct page *page);
> > void putback_active_hugepages(struct list_head *l);
> > void migrate_hugepage_add(struct page *page, struct list_head *list);
> > +int is_hugepage_movable(struct page *page);
> > void copy_huge_page(struct page *dst, struct page *src);
> >
> > extern unsigned long hugepages_treat_as_movable;
> > @@ -136,6 +137,7 @@ static inline int dequeue_hwpoisoned_huge_page(struct page *page)
> > #define putback_active_hugepage(p) 0
> > #define putback_active_hugepages(l) 0
> > #define migrate_hugepage_add(p, l) 0
> > +#define is_hugepage_movable(x) 0
> > static inline void copy_huge_page(struct page *dst, struct page *src)
> > {
> > }
> > @@ -358,6 +360,10 @@ static inline int hstate_index(struct hstate *h)
> > return h - hstates;
> > }
> >
> > +extern void dissolve_free_huge_page(struct page *page);
> > +extern void dissolve_free_huge_pages(unsigned long start_pfn,
> > + unsigned long end_pfn);
> > +
> > #else
> > struct hstate {};
> > #define alloc_huge_page(v, a, r) NULL
> > @@ -378,6 +384,8 @@ static inline unsigned int pages_per_huge_page(struct hstate *h)
> > }
> > #define hstate_index_to_shift(index) 0
> > #define hstate_index(h) 0
> > +#define dissolve_free_huge_page(p) 0
> > +#define dissolve_free_huge_pages(s, e) 0
> > #endif
> >
> > #endif /* _LINUX_HUGETLB_H */
> > diff --git v3.8.orig/mm/hugetlb.c v3.8/mm/hugetlb.c
> > index ccf9995..c28e6c9 100644
> > --- v3.8.orig/mm/hugetlb.c
> > +++ v3.8/mm/hugetlb.c
> > @@ -843,6 +843,30 @@ static int free_pool_huge_page(struct hstate *h, nodemask_t *nodes_allowed,
> > return ret;
> > }
> >
> > +/* Dissolve a given free hugepage into free pages. */
> > +void dissolve_free_huge_page(struct page *page)
> > +{
> > + if (PageHuge(page) && !page_count(page)) {
>
> Could you clarify why you are cheking page_count here? I assume it is to
> make sure the page is free but what prevents it being increased before
> you take hugetlb_lock?
There's nothing to prevent it, so it's not safe to check refcount outside
hugetlb_lock.
> > + struct hstate *h = page_hstate(page);
> > + int nid = page_to_nid(page);
> > + spin_lock(&hugetlb_lock);
> > + list_del(&page->lru);
> > + h->free_huge_pages--;
> > + h->free_huge_pages_node[nid]--;
> > + update_and_free_page(h, page);
> > + spin_unlock(&hugetlb_lock);
> > + }
> > +}
> > +
> > +/* Dissolve free hugepages in a given pfn range. Used by memory hotplug. */
> > +void dissolve_free_huge_pages(unsigned long start_pfn, unsigned long end_pfn)
> > +{
> > + unsigned long pfn;
> > + unsigned int step = 1 << (HUGETLB_PAGE_ORDER);
>
> hugetlb pages could be present in different sizes so this doesn't work
> in general. You need to to get order from page_hstate.
OK.
> > + for (pfn = start_pfn; pfn < end_pfn; pfn += step)
> > + dissolve_free_huge_page(pfn_to_page(pfn));
> > +}
> > +
> > static struct page *alloc_buddy_huge_page(struct hstate *h, int nid)
> > {
> > struct page *page;
> > @@ -3158,6 +3182,25 @@ static int is_hugepage_on_freelist(struct page *hpage)
> > return 0;
> > }
> >
> > +/* Returns true for head pages of in-use hugepages, otherwise returns false. */
> > +int is_hugepage_movable(struct page *hpage)
> > +{
> > + struct page *page;
> > + struct page *tmp;
> > + struct hstate *h = page_hstate(hpage);
> > + int ret = 0;
> > +
> > + VM_BUG_ON(!PageHuge(hpage));
> > + if (PageTail(hpage))
> > + return 0;
> > + spin_lock(&hugetlb_lock);
> > + list_for_each_entry_safe(page, tmp, &h->hugepage_activelist, lru)
> > + if (page == hpage)
> > + ret = 1;
> > + spin_unlock(&hugetlb_lock);
> > + return ret;
> > +}
> > +
> > /*
> > * This function is called from memory failure code.
> > * Assume the caller holds page lock of the head page.
> > diff --git v3.8.orig/mm/memory_hotplug.c v3.8/mm/memory_hotplug.c
> > index d04ed87..6418de2 100644
> > --- v3.8.orig/mm/memory_hotplug.c
> > +++ v3.8/mm/memory_hotplug.c
> > @@ -29,6 +29,7 @@
> > #include <linux/suspend.h>
> > #include <linux/mm_inline.h>
> > #include <linux/firmware-map.h>
> > +#include <linux/hugetlb.h>
> >
> > #include <asm/tlbflush.h>
> >
> > @@ -985,10 +986,12 @@ static int test_pages_in_a_zone(unsigned long start_pfn, unsigned long end_pfn)
> > }
> >
> > /*
> > - * Scanning pfn is much easier than scanning lru list.
> > - * Scan pfn from start to end and Find LRU page.
> > + * Scan pfn range [start,end) to find movable/migratable pages (LRU pages
> > + * and hugepages). We scan pfn because it's much easier than scanning over
> > + * linked list. This function returns the pfn of the first found movable
> > + * page if it's found, otherwise 0.
> > */
> > -static unsigned long scan_lru_pages(unsigned long start, unsigned long end)
> > +static unsigned long scan_movable_pages(unsigned long start, unsigned long end)
> > {
> > unsigned long pfn;
> > struct page *page;
> > @@ -997,6 +1000,12 @@ static unsigned long scan_lru_pages(unsigned long start, unsigned long end)
> > page = pfn_to_page(pfn);
> > if (PageLRU(page))
> > return pfn;
> > + if (PageHuge(page)) {
> > + if (is_hugepage_movable(page))
> > + return pfn;
> > + else
> > + pfn += (1 << compound_order(page)) - 1;
> > + }
>
> scan_lru_pages's name gets really confusing after this change because
> hugetlb pages are not on the LRU. Maybe it would be good to rename it.
Yes, and that's done in right above chunk.
>
> > }
> > }
> > return 0;
> > @@ -1019,6 +1028,30 @@ do_migrate_range(unsigned long start_pfn, unsigned long end_pfn)
> > page = pfn_to_page(pfn);
> > if (!get_page_unless_zero(page))
> > continue;
>
> All tail pages have 0 reference count (according to prep_compound_page)
> so they would be skipped anyway. This makes the below pfn tweaks
> pointless.
I was totally mistaken about what we should do here, sorry. If we call
do_migrate_range() for 1GB hugepage, we should return with error (maybe -EBUSY)
instead of just skipping it, otherwise the caller __offline_pages() repeats
'goto repeat' until timeout. In order to do that, we had better insert
if(PageHuge) block before getting refcount. And ...
> > + if (PageHuge(page)) {
> > + /*
> > + * Larger hugepage (1GB for x86_64) is larger than
> > + * memory block, so pfn scan can start at the tail
> > + * page of larger hugepage. In such case,
> > + * we simply skip the hugepage and move the cursor
> > + * to the last tail page.
> > + */
> > + if (PageTail(page)) {
> > + struct page *head = compound_head(page);
> > + pfn = page_to_pfn(head) +
> > + (1 << compound_order(head)) - 1;
> > + put_page(page);
> > + continue;
> > + }
> > + pfn = (1 << compound_order(page)) - 1;
> > + if (huge_page_size(page_hstate(page)) != PMD_SIZE) {
> > + put_page(page);
> > + continue;
> > + }
>
> There might be other hugepage sizes which fit into memblock so this test
> doesn't seem right.
yes, so compound_order(head) > PFN_SECTION_SHIFT would be better.
I'll replace this chunk with the following if I don't get any other
suggestion.
@@ -1017,6 +1026,21 @@ do_migrate_range(unsigned long start_pfn, unsigned long end_pfn)
if (!pfn_valid(pfn))
continue;
page = pfn_to_page(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;
+ }
+ if (!get_page_unless_zero(page))
+ continue;
+ list_move_tail(&head->lru, &source);
+ move_pages -= 1 << compound_order(head);
+ continue;
+ }
+
if (!get_page_unless_zero(page))
continue;
/*
Thanks,
Naoya
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