When __get_user_pages() is called with FOLL_DURABLE flag, ensure that no
page in CMA pageblocks gets locked. This workarounds the permanent
migration failures caused by locking the pages by get_user_pages() call for
a long period of time.
Signed-off-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
Signed-off-by: Kyungmin Park <kyungmin.park@xxxxxxxxxxx>
---
mm/internal.h | 12 ++++++++++++
mm/memory.c | 43 +++++++++++++++++++++++++++++++++++++++++++
2 files changed, 55 insertions(+)
diff --git a/mm/internal.h b/mm/internal.h
index 8562de0..a290d04 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -105,6 +105,18 @@ extern void prep_compound_page(struct page *page, unsigned long order);
extern bool is_free_buddy_page(struct page *page);
#endif
+#ifdef CONFIG_CMA
+static inline int is_cma_page(struct page *page)
+{
+ unsigned mt = get_pageblock_migratetype(page);
+ if (mt == MIGRATE_ISOLATE || mt == MIGRATE_CMA)
+ return true;
+ return false;
+}
+#else
+#define is_cma_page(page) 0
+#endif
+
#if defined CONFIG_COMPACTION || defined CONFIG_CMA
/*
diff --git a/mm/memory.c b/mm/memory.c
index 2b9c2dd..f81b273 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1650,6 +1650,45 @@ static inline int stack_guard_page(struct vm_area_struct *vma, unsigned long add
}
/**
+ * replace_cma_page() - migrate page out of CMA page blocks
+ * @page: source page to be migrated
+ *
+ * Returns either the old page (if migration was not possible) or the pointer
+ * to the newly allocated page (with additional reference taken).
+ *
+ * get_user_pages() might take a reference to a page for a long period of time,
+ * what prevent such page from migration. This is fatal to the preffered usage
+ * pattern of CMA pageblocks. This function replaces the given user page with
+ * a new one allocated from NON-MOVABLE pageblock, so locking CMA page can be
+ * avoided.
+ */
+static inline struct page *migrate_replace_cma_page(struct page *page)
+{
+ struct page *newpage = alloc_page(GFP_HIGHUSER);
+
+ if (!newpage)
+ goto out;
+
+ /*
+ * Take additional reference to the new page to ensure it won't get
+ * freed after migration procedure end.
+ */
+ get_page_foll(newpage);
+
+ if (migrate_replace_page(page, newpage) == 0)
+ return newpage;
+
+ put_page(newpage);
+ __free_page(newpage);
+out:
+ /*
+ * Migration errors in case of get_user_pages() might not
+ * be fatal to CMA itself, so better don't fail here.
+ */
+ return page;
+}
+
+/**
* __get_user_pages() - pin user pages in memory
* @tsk: task_struct of target task
* @mm: mm_struct of target mm
@@ -1884,6 +1923,10 @@ long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
}
if (IS_ERR(page))
return i ? i : PTR_ERR(page);
+
+ if ((gup_flags & FOLL_DURABLE) && is_cma_page(page))
+ page = migrate_replace_cma_page(page);
+
if (pages) {
pages[i] = page;
--
1.7.9.5
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