[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, 8 insertions, 3 deletions

diff --git a/mm/filemap_xip.c b/mm/filemap_xip.c
index 8c199f537732..9354ee279b13 100644
--- a/mm/filemap_xip.c
+++ b/mm/filemap_xip.c
@@ -174,6 +174,7 @@ __xip_unmap (struct address_space * mapping,
         unsigned long address;
         pte_t *pte;
         pte_t pteval;
+        struct page *page = ZERO_PAGE(address);
 
         spin_lock(&mapping->i_mmap_lock);
         vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) {
@@ -185,15 +186,17 @@ __xip_unmap (struct address_space * mapping,
                  * We need the page_table_lock to protect us from page faults,
                  * munmap, fork, etc...
                  */
-                pte = page_check_address(ZERO_PAGE(address), mm,
-                                         address);
+                pte = page_check_address(page, mm, address);
                 if (!IS_ERR(pte)) {
                         /* Nuke the page table entry. */
                         flush_cache_page(vma, address, pte_pfn(*pte));
                         pteval = ptep_clear_flush(vma, address, pte);
+                        page_remove_rmap(page);
+                        dec_mm_counter(mm, file_rss);
                         BUG_ON(pte_dirty(pteval));
                         pte_unmap(pte);
                         spin_unlock(&mm->page_table_lock);
+                        page_cache_release(page);
                 }
         }
         spin_unlock(&mapping->i_mmap_lock);
@@ -228,7 +231,7 @@ xip_file_nopage(struct vm_area_struct * area,
 
         page = mapping->a_ops->get_xip_page(mapping, pgoff*(PAGE_SIZE/512), 0);
         if (!IS_ERR(page)) {
-                return page;
+                goto out;
         }
         if (PTR_ERR(page) != -ENODATA)
                 return NULL;
@@ -249,6 +252,8 @@ xip_file_nopage(struct vm_area_struct * area,
                 page = ZERO_PAGE(address);
         }
 
+out:
+        page_cache_get(page);
         return page;
 }