[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 22533cc..e75a954 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -324,7 +324,7 @@
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 33261f1..9d6fbee 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -71,6 +71,7 @@
* 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 e249088..d7ca7de 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1498,7 +1498,7 @@
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 @@
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 @@
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 f853c6d..4107f64 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -435,6 +435,26 @@
}
/**
+ * 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
* @vma: the vm area in which the mapping is added
@@ -445,20 +465,27 @@
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