[PATCH] mm: rmap optimisation

Optimise rmap functions by minimising atomic operations when we know there
will be no concurrent modifications.

Signed-off-by: Nick Piggin <npiggin@suse.de>
Cc: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/fs/exec.c b/fs/exec.c
index 22533cce061165023d43cfedac7310c2e4d414b7..e75a9548da8ef397b4cec6e1527f00d81e6fd5c4 100644 (file)
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -324,7 +324,7 @@ void install_arg_page(struct vm_area_struct *vma,
        lru_cache_add_active(page);
        set_pte_at(mm, address, pte, pte_mkdirty(pte_mkwrite(mk_pte(
                                        page, vma->vm_page_prot))));
-       page_add_anon_rmap(page, vma, address);
+       page_add_new_anon_rmap(page, vma, address);
        pte_unmap_unlock(pte, ptl);
 
        /* no need for flush_tlb */

diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index 33261f1d22395fba7d9a54a45efcaff12493336d..9d6fbeef210472b21a7a974677303183747bc06e 100644 (file)
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -71,6 +71,7 @@ void __anon_vma_link(struct vm_area_struct *);
  * rmap interfaces called when adding or removing pte of page
  */
 void page_add_anon_rmap(struct page *, struct vm_area_struct *, unsigned long);
+void page_add_new_anon_rmap(struct page *, struct vm_area_struct *, unsigned long);
 void page_add_file_rmap(struct page *);
 void page_remove_rmap(struct page *);
 

diff --git a/mm/memory.c b/mm/memory.c
index e249088908c436940386cbf161f1b6d0c7c39c0b..d7ca7de10f4d7db82d32d92de1c2f2c1a548c2fb 100644 (file)
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1498,7 +1498,7 @@ gotten:
                update_mmu_cache(vma, address, entry);
                lazy_mmu_prot_update(entry);
                lru_cache_add_active(new_page);
-               page_add_anon_rmap(new_page, vma, address);
+               page_add_new_anon_rmap(new_page, vma, address);
 
                /* Free the old page.. */
                new_page = old_page;
@@ -1978,7 +1978,7 @@ static int do_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma,
                inc_mm_counter(mm, anon_rss);
                lru_cache_add_active(page);
                SetPageReferenced(page);
-               page_add_anon_rmap(page, vma, address);
+               page_add_new_anon_rmap(page, vma, address);
        } else {
                /* Map the ZERO_PAGE - vm_page_prot is readonly */
                page = ZERO_PAGE(address);
@@ -2109,7 +2109,7 @@ retry:
                if (anon) {
                        inc_mm_counter(mm, anon_rss);
                        lru_cache_add_active(new_page);
-                       page_add_anon_rmap(new_page, vma, address);
+                       page_add_new_anon_rmap(new_page, vma, address);
                } else {
                        inc_mm_counter(mm, file_rss);
                        page_add_file_rmap(new_page);

diff --git a/mm/rmap.c b/mm/rmap.c
index f853c6def15915602e484afdd3a741099d543887..4107f64ff749e53d7b9ba0eec72e0dfa4862f9aa 100644 (file)
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -434,6 +434,26 @@ int page_referenced(struct page *page, int is_locked)
        return referenced;
 }
 
+/**
+ * page_set_anon_rmap - setup new anonymous rmap
+ * @page:      the page to add the mapping to
+ * @vma:       the vm area in which the mapping is added
+ * @address:   the user virtual address mapped
+ */
+static void __page_set_anon_rmap(struct page *page,
+       struct vm_area_struct *vma, unsigned long address)
+{
+       struct anon_vma *anon_vma = vma->anon_vma;
+
+       BUG_ON(!anon_vma);
+       anon_vma = (void *) anon_vma + PAGE_MAPPING_ANON;
+       page->mapping = (struct address_space *) anon_vma;
+
+       page->index = linear_page_index(vma, address);
+
+       inc_page_state(nr_mapped);
+}
+
 /**
  * page_add_anon_rmap - add pte mapping to an anonymous page
  * @page:      the page to add the mapping to
@@ -445,20 +465,27 @@ int page_referenced(struct page *page, int is_locked)
 void page_add_anon_rmap(struct page *page,
        struct vm_area_struct *vma, unsigned long address)
 {
-       if (atomic_inc_and_test(&page->_mapcount)) {
-               struct anon_vma *anon_vma = vma->anon_vma;
-
-               BUG_ON(!anon_vma);
-               anon_vma = (void *) anon_vma + PAGE_MAPPING_ANON;
-               page->mapping = (struct address_space *) anon_vma;
-
-               page->index = linear_page_index(vma, address);
-
-               inc_page_state(nr_mapped);
-       }
+       if (atomic_inc_and_test(&page->_mapcount))
+               __page_set_anon_rmap(page, vma, address);
        /* else checking page index and mapping is racy */
 }
 
+/*
+ * page_add_new_anon_rmap - add pte mapping to a new anonymous page
+ * @page:      the page to add the mapping to
+ * @vma:       the vm area in which the mapping is added
+ * @address:   the user virtual address mapped
+ *
+ * Same as page_add_anon_rmap but must only be called on *new* pages.
+ * This means the inc-and-test can be bypassed.
+ */
+void page_add_new_anon_rmap(struct page *page,
+       struct vm_area_struct *vma, unsigned long address)
+{
+       atomic_set(&page->_mapcount, 0); /* elevate count by 1 (starts at -1) */
+       __page_set_anon_rmap(page, vma, address);
+}
+
 /**
  * page_add_file_rmap - add pte mapping to a file page
  * @page: the page to add the mapping to