On Thu, Feb 21, 2013 at 02:41:47PM -0500, Naoya Horiguchi wrote: > Date: Thu, 21 Feb 2013 14:41:47 -0500 > From: Naoya Horiguchi > To: linux-mm@kvack.org > Cc: Andrew Morton , Mel Gorman , > Hugh Dickins , KOSAKI Motohiro > , Andi Kleen , > linux-kernel@vger.kernel.org > Subject: [PATCH 8/9] memory-hotplug: enable memory hotplug to handle > hugepage > > 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. > > Signed-off-by: Naoya Horiguchi > --- > 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)) { > + 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); > + 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; I don't understand the logic here. 1) page is not removed why tmp is used? 2) why hitting (page ==hpage) but not breaking from the loop? > + spin_unlock(&hugetlb_lock); > + return ret; > +} > + > [...]