[PATCH] misc rmap speedups

Even a BUG_ON() makes a measurable difference.  So remove some gratuitous
ones which will just trigger a null pointer deref anyway.

Also remove some debug code which isn't really being maintained any more.

Also replace (effectively):

	test_bit(N, foo);
	set_bit(N, foo);

with

	set_bit(N, foo);
	test_bit(N, foo);

In the first case we'll go onto the bus twice: once for the cache miss and
once to get exclusive write access.  In the second case we only go on the bus
once.  I think.  Certainly this trick chaved 40% off the cost of
shrink_list() when I did it there...

This patch is worth 1% or so on the bash script testing.

diff --git a/mm/rmap.c b/mm/rmap.c
index 6575b5cafa38415cf971cb48b0402960bbc43b8f..ff69a1acfa2dac4e11f78342e5d5156103371d0a 100644 (file)
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -170,43 +170,10 @@ page_add_rmap(struct page *page, pte_t *ptep, struct pte_chain *pte_chain)
        pte_addr_t pte_paddr = ptep_to_paddr(ptep);
        struct pte_chain *cur_pte_chain;
 
-#ifdef DEBUG_RMAP
-       if (!page || !ptep)
-               BUG();
-       if (!pte_present(*ptep))
-               BUG();
-       if (!ptep_to_mm(ptep))
-               BUG();
-#endif
-
-       if (!pfn_valid(page_to_pfn(page)) || PageReserved(page))
-               return pte_chain;
-
        pte_chain_lock(page);
 
-#ifdef DEBUG_RMAP
-       /*
-        * This stuff needs help to get up to highmem speed.
-        */
-       {
-               struct pte_chain *pc;
-               int i;
-
-               if (PageDirect(page)) {
-                       if (page->pte.direct == pte_paddr)
-                               BUG();
-               } else {
-                       for (pc = page->pte.chain; pc; pc=pte_chain_next(pc)) {
-                               for (i = 0; i < NRPTE; i++) {
-                                       pte_addr_t p = pc->ptes[i];
-
-                                       if (p && p == pte_paddr)
-                                               BUG();
-                               }
-                       }
-               }
-       }
-#endif
+       if (!pfn_valid(page_to_pfn(page)) || PageReserved(page))
+               goto out;
 
        if (page->pte.direct == 0) {
                page->pte.direct = pte_paddr;
@@ -253,19 +220,18 @@ out:
  * the page.
  * Caller needs to hold the mm->page_table_lock.
  */
-void page_remove_rmap(struct page * page, pte_t * ptep)
+void page_remove_rmap(struct page *page, pte_t *ptep)
 {
        pte_addr_t pte_paddr = ptep_to_paddr(ptep);
        struct pte_chain *pc;
 
-       if (!page || !ptep)
-               BUG();
+       pte_chain_lock(page);
+
        if (!pfn_valid(page_to_pfn(page)) || PageReserved(page))
-               return;
-       if (!page_mapped(page))
-               return;         /* remap_page_range() from a driver? */
+               goto out_unlock;
 
-       pte_chain_lock(page);
+       if (!page_mapped(page))
+               goto out_unlock;        /* remap_page_range() from a driver? */
 
        if (PageDirect(page)) {
                if (page->pte.direct == pte_paddr) {
@@ -304,27 +270,11 @@ void page_remove_rmap(struct page * page, pte_t * ptep)
                        }
                }
        }
-#ifdef DEBUG_RMAP
-       /* Not found. This should NEVER happen! */
-       printk(KERN_ERR "page_remove_rmap: pte_chain %p not present.\n", ptep);
-       printk(KERN_ERR "page_remove_rmap: only found: ");
-       if (PageDirect(page)) {
-               printk("%llx", (u64)page->pte.direct);
-       } else {
-               for (pc = page->pte.chain; pc; pc = pte_chain_next(pc)) {
-                       int i;
-                       for (i = 0; i < NRPTE; i++)
-                               printk(" %d:%llx", i, (u64)pc->ptes[i]);
-               }
-       }
-       printk("\n");
-       printk(KERN_ERR "page_remove_rmap: driver cleared PG_reserved ?\n");
-#endif
-
 out:
-       pte_chain_unlock(page);
        if (!page_mapped(page))
                dec_page_state(nr_mapped);
+out_unlock:
+       pte_chain_unlock(page);
        return;
 }