[PATCH] core remove PageReserved

Remove PageReserved() calls from core code by tightening VM_RESERVED
handling in mm/ to cover PageReserved functionality.

PageReserved special casing is removed from get_page and put_page.

All setting and clearing of PageReserved is retained, and it is now flagged
in the page_alloc checks to help ensure we don't introduce any refcount
based freeing of Reserved pages.

MAP_PRIVATE, PROT_WRITE of VM_RESERVED regions is tentatively being
deprecated.  We never completely handled it correctly anyway, and is be
reintroduced in future if required (Hugh has a proof of concept).

Once PageReserved() calls are removed from kernel/power/swsusp.c, and all
arch/ and driver code, the Set and Clear calls, and the PG_reserved bit can
be trivially removed.

Last real user of PageReserved is swsusp, which uses PageReserved to
determine whether a struct page points to valid memory or not.  This still
needs to be addressed (a generic page_is_ram() should work).

A last caveat: the ZERO_PAGE is now refcounted and managed with rmap (and
thus mapcounted and count towards shared rss).  These writes to the struct
page could cause excessive cacheline bouncing on big systems.  There are a
number of ways this could be addressed if it is an issue.

Signed-off-by: Nick Piggin <npiggin@suse.de>

Refcount bug fix for filemap_xip.c

Signed-off-by: Carsten Otte <cotte@de.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 16 insertions, 9 deletions

diff --git a/kernel/power/swsusp.c b/kernel/power/swsusp.c
index 10bc5ec496d7..016504ccfccf 100644
--- a/kernel/power/swsusp.c
+++ b/kernel/power/swsusp.c
@@ -578,15 +578,23 @@ static int save_highmem_zone(struct zone *zone)
                         continue;
                 page = pfn_to_page(pfn);
                 /*
-                 * This condition results from rvmalloc() sans vmalloc_32()
-                 * and architectural memory reservations. This should be
-                 * corrected eventually when the cases giving rise to this
-                 * are better understood.
+                 * PageReserved results from rvmalloc() sans vmalloc_32()
+                 * and architectural memory reservations.
+                 *
+                 * rvmalloc should not cause this, because all implementations
+                 * appear to always be using vmalloc_32 on architectures with
+                 * highmem. This is a good thing, because we would like to save
+                 * rvmalloc pages.
+                 *
+                 * It appears to be triggered by pages which do not point to
+                 * valid memory (see arch/i386/mm/init.c:one_highpage_init(),
+                 * which sets PageReserved if the page does not point to valid
+                 * RAM.
+                 *
+                 * XXX: must remove usage of PageReserved!
                  */
-                if (PageReserved(page)) {
-                        printk("highmem reserved page?!\n");
+                if (PageReserved(page))
                         continue;
-                }
                 BUG_ON(PageNosave(page));
                 if (PageNosaveFree(page))
                         continue;
@@ -672,10 +680,9 @@ static int saveable(struct zone * zone, unsigned long * zone_pfn)
                 return 0;
 
         page = pfn_to_page(pfn);
-        BUG_ON(PageReserved(page) && PageNosave(page));
         if (PageNosave(page))
                 return 0;
-        if (PageReserved(page) && pfn_is_nosave(pfn)) {
+        if (pfn_is_nosave(pfn)) {
                 pr_debug("[nosave pfn 0x%lx]", pfn);
                 return 0;
         }