1 files changed, 28 insertions, 3 deletions

diff --git a/include/linux/mm.h b/include/linux/mm.h
index ecdabf3597ae..af0595bef9c8 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -462,7 +462,6 @@ static inline void page_mapcount_reset(struct page *page)
 
 static inline int page_mapcount(struct page *page)
 {
-	VM_BUG_ON_PAGE(PageSlab(page), page);
 	return atomic_read(&page->_mapcount) + 1;
 }
 
@@ -504,6 +503,15 @@ static inline void get_huge_page_tail(struct page *page)
 
 extern bool __get_page_tail(struct page *page);
 
+static inline int page_ref_count(struct page *page)
+{
+	return atomic_read(&page->_count);
+}
+
+/* 127: arbitrary random number, small enough to assemble well */
+#define page_ref_zero_or_close_to_overflow(page) \
+	((unsigned int) atomic_read(&page->_count) + 127u <= 127u)
+
 static inline void get_page(struct page *page)
 {
 	if (unlikely(PageTail(page)))
@@ -513,10 +521,22 @@ static inline void get_page(struct page *page)
 	 * Getting a normal page or the head of a compound page
 	 * requires to already have an elevated page->_count.
 	 */
-	VM_BUG_ON_PAGE(atomic_read(&page->_count) <= 0, page);
+	VM_BUG_ON_PAGE(page_ref_zero_or_close_to_overflow(page), page);
 	atomic_inc(&page->_count);
 }
 
+static inline __must_check bool try_get_page(struct page *page)
+{
+	if (unlikely(PageTail(page)))
+		if (likely(__get_page_tail(page)))
+			return true;
+
+	if (WARN_ON_ONCE(atomic_read(&page->_count) <= 0))
+		return false;
+	atomic_inc(&page->_count);
+	return true;
+}
+
 static inline struct page *virt_to_head_page(const void *x)
 {
 	struct page *page = virt_to_page(x);
@@ -1120,6 +1140,10 @@ void unmap_vmas(struct mmu_gather *tlb, struct vm_area_struct *start_vma,
  * followed by taking the mmap_sem for writing before modifying the
  * vmas or anything the coredump pretends not to change from under it.
  *
+ * It also has to be called when mmgrab() is used in the context of
+ * the process, but then the mm_count refcount is transferred outside
+ * the context of the process to run down_write() on that pinned mm.
+ *
  * NOTE: find_extend_vma() called from GUP context is the only place
  * that can modify the "mm" (notably the vm_start/end) under mmap_sem
  * for reading and outside the context of the process, so it is also
@@ -1819,6 +1843,7 @@ extern int __meminit init_per_zone_wmark_min(void);
 extern void mem_init(void);
 extern void __init mmap_init(void);
 extern void show_mem(unsigned int flags);
+extern long si_mem_available(void);
 extern void si_meminfo(struct sysinfo * val);
 extern void si_meminfo_node(struct sysinfo *val, int nid);
 
@@ -2008,7 +2033,7 @@ int write_one_page(struct page *page, int wait);
 void task_dirty_inc(struct task_struct *tsk);
 
 /* readahead.c */
-#define VM_MAX_READAHEAD	512	/* kbytes */
+#define VM_MAX_READAHEAD	CONFIG_VM_MAX_READAHEAD	/* kbytes */
 #define VM_MIN_READAHEAD	16	/* kbytes (includes current page) */
 
 int force_page_cache_readahead(struct address_space *mapping, struct file *filp,