How about moving the flags into the union? A bit messy, but we don't
have to play games with __packed__.
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 1210a8e41fad..f374d2f06255 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -68,16 +68,22 @@ struct mem_cgroup;
#endif
struct page {
- unsigned long flags; /* Atomic flags, some possibly
- * updated asynchronously */
/*
- * Five words (20/40 bytes) are available in this union.
- * WARNING: bit 0 of the first word is used for PageTail(). That
- * means the other users of this union MUST NOT use the bit to
+ * This union is six words (24 / 48 bytes) in size.
+ * The first word is reserved for atomic flags, often updated
+ * asynchronously. Use the PageFoo() macros to access it. Some
+ * of the flags can be reused for your own purposes, but the
+ * word as a whole often contains other information and overwriting
+ * it will cause functions like page_zone() and page_node() to stop
+ * working correctly.
+ *
+ * Bit 0 of the second word is used for PageTail(). That
+ * means the other users of this union MUST leave the bit zero to
* avoid collision and false-positive PageTail().
*/
union {
struct { /* Page cache and anonymous pages */
+ unsigned long flags;
/**
* @lru: Pageout list, eg. active_list protected by
* lruvec->lru_lock. Sometimes used as a generic list
@@ -96,6 +102,8 @@ struct page {
unsigned long private;
};
struct { /* page_pool used by netstack */
+ unsigned long _pp_flags;
+ unsigned long _pp_pad;
/**
* @dma_addr: might require a 64-bit value even on
* 32-bit architectures.
@@ -103,6 +111,7 @@ struct page {
dma_addr_t dma_addr;
};
struct { /* slab, slob and slub */
+ unsigned long _slab_flags;
union {
struct list_head slab_list;
struct { /* Partial pages */
@@ -130,6 +139,7 @@ struct page {
};
};
struct { /* Tail pages of compound page */
+ unsigned long _tail1_flags;
unsigned long compound_head; /* Bit zero is set */
/* First tail page only */
@@ -139,12 +149,14 @@ struct page {
unsigned int compound_nr; /* 1 << compound_order */
};
struct { /* Second tail page of compound page */
+ unsigned long _tail2_flags;
unsigned long _compound_pad_1; /* compound_head */
atomic_t hpage_pinned_refcount;
/* For both global and memcg */
struct list_head deferred_list;
};
struct { /* Page table pages */
+ unsigned long _pt_flags;
unsigned long _pt_pad_1; /* compound_head */
pgtable_t pmd_huge_pte; /* protected by page->ptl */
unsigned long _pt_pad_2; /* mapping */
@@ -159,6 +171,7 @@ struct page {
#endif
};
struct { /* ZONE_DEVICE pages */
+ unsigned long _zd_flags;
/** @pgmap: Points to the hosting device page map. */
struct dev_pagemap *pgmap;
void *zone_device_data;
@@ -174,8 +187,11 @@ struct page {
*/
};
- /** @rcu_head: You can use this to free a page by RCU. */
- struct rcu_head rcu_head;
+ struct {
+ unsigned long _rcu_flags;
+ /** @rcu_head: You can use this to free a page by RCU.
*/
+ struct rcu_head rcu_head;
+ };
};
union { /* This union is 4 bytes in size. */
