This changes netback to use struct page's mapping field instead of the
index one, and the PageForeign logic the other way around. That way,
CONFIG_SPLIT_PTLOCK_CPUS doesn't have to be suppressed anymore for x86.
After that adjustment, the sparse tree's mm/Kconfig should be identical
to native and could hence be deleted.
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxxxx>
Index: head-2007年02月27日/drivers/xen/netback/netback.c
===================================================================
--- head-2007年02月27日.orig/drivers/xen/netback/netback.c 2007年02月27日 
16:31:12.000000000 +0100
+++ head-2007年02月27日/drivers/xen/netback/netback.c 2007年03月01日 
15:23:00.000000000 +0100
@@ -40,6 +40,9 @@
 
 /*#define NETBE_DEBUG_INTERRUPT*/
 
+/* extra field used in struct page */
+#define netif_page_index(pg) (*(long *)&(pg)->mapping)
+
 struct netbk_rx_meta {
 skb_frag_t frag;
 int id;
@@ -352,7 +355,7 @@ static u16 netbk_gop_frag(netif_t *netif
 copy_gop->flags = GNTCOPY_dest_gref;
 if (PageForeign(page)) {
 struct pending_tx_info *src_pend =
- &pending_tx_info[page->index];
+ &pending_tx_info[netif_page_index(page)];
 copy_gop->source.domid = src_pend->netif->domid;
 copy_gop->source.u.ref = src_pend->req.gref;
 copy_gop->flags |= GNTCOPY_source_gref;
@@ -1327,7 +1330,7 @@ static void netif_page_release(struct pa
 /* Ready for next use. */
 init_page_count(page);
 
- netif_idx_release(page->index);
+ netif_idx_release(netif_page_index(page));
 }
 
 irqreturn_t netif_be_int(int irq, void *dev_id, struct pt_regs *regs)
@@ -1457,7 +1460,7 @@ static int __init netback_init(void)
 for (i = 0; i < MAX_PENDING_REQS; i++) {
 page = mmap_pages[i];
 SetPageForeign(page, netif_page_release);
- page->index = i;
+ netif_page_index(page) = i;
 }
 
 pending_cons = 0;
Index: head-2007年02月27日/include/linux/page-flags.h
===================================================================
--- head-2007年02月27日.orig/include/linux/page-flags.h 2007年02月27日 
16:26:22.000000000 +0100
+++ head-2007年02月27日/include/linux/page-flags.h 2007年03月01日 15:15:29.000000000 
+0100
@@ -252,14 +252,14 @@ static inline void SetPageUptodate(struc
 #define PageForeign(page) test_bit(PG_foreign, &(page)->flags)
 #define SetPageForeign(page, dtor) do { \
 set_bit(PG_foreign, &(page)->flags); \
- (page)->mapping = (void *)dtor; \
+ (page)->index = (long)(dtor); \
 } while (0)
 #define ClearPageForeign(page) do { \
 clear_bit(PG_foreign, &(page)->flags); \
- (page)->mapping = NULL; \
+ (page)->index = 0; \
 } while (0)
 #define PageForeignDestructor(page) \
- ( (void (*) (struct page *)) (page)->mapping )(page)
+ ( (void (*) (struct page *)) (page)->index )(page)
 
 struct page; /* forward declaration */
 
Index: head-2007年02月27日/mm/Kconfig
===================================================================
--- head-2007年02月27日.orig/mm/Kconfig 2007年02月27日 16:23:14.000000000 +0100
+++ head-2007年02月27日/mm/Kconfig 2007年03月01日 15:16:15.000000000 +0100
@@ -127,14 +127,11 @@ config MEMORY_HOTPLUG_SPARSE
 # Default to 4 for wider testing, though 8 might be more appropriate.
 # ARM's adjust_pte (unused if VIPT) depends on mm-wide page_table_lock.
 # PA-RISC 7xxx's spinlock_t would enlarge struct page from 32 to 44 bytes.
-# XEN on x86 architecture uses the mapping field on pagetable pages to store a
-# pointer to the destructor. This conflicts with pte_lock_deinit().
 #
 config SPLIT_PTLOCK_CPUS
 int
 default "4096" if ARM && !CPU_CACHE_VIPT
 default "4096" if PARISC && !PA20
- default "4096" if X86_XEN || X86_64_XEN
 default "4"
 
 #
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