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.
> 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?
> + 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.
> + 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.
> }
> }
> 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.
> + 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.
> + list_move_tail(&page->lru, &source);
> + move_pages -= 1 << compound_order(page);
> + continue;
> + }
> /*
> * We can skip free pages. And we can only deal with pages on
> * LRU.
[...]
--
Michal Hocko
SUSE Labs
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