[PATCHv2 02/28] rmap: introduce rmap_walk_locked()

From: Kirill A. Shutemov
Date: Thu Feb 11 2016 - 09:31:29 EST


rmap_walk_locked() is the same as rmap_walk(), but caller takes care
about relevant rmap lock.

It's preparation to switch THP splitting from custom rmap walk in
freeze_page()/unfreeze_page() to generic one.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
---
include/linux/rmap.h | 1 +
mm/rmap.c | 41 ++++++++++++++++++++++++++++++++---------
2 files changed, 33 insertions(+), 9 deletions(-)

diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index a07f42bedda3..a5875e9b4a27 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -266,6 +266,7 @@ struct rmap_walk_control {
};

int rmap_walk(struct page *page, struct rmap_walk_control *rwc);
+int rmap_walk_locked(struct page *page, struct rmap_walk_control *rwc);

#else /* !CONFIG_MMU */

diff --git a/mm/rmap.c b/mm/rmap.c
index 02f0bfc3c80a..30b739ce0ffa 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1715,14 +1715,21 @@ static struct anon_vma *rmap_walk_anon_lock(struct page *page,
* vm_flags for that VMA. That should be OK, because that vma shouldn't be
* LOCKED.
*/
-static int rmap_walk_anon(struct page *page, struct rmap_walk_control *rwc)
+static int rmap_walk_anon(struct page *page, struct rmap_walk_control *rwc,
+ bool locked)
{
struct anon_vma *anon_vma;
pgoff_t pgoff;
struct anon_vma_chain *avc;
int ret = SWAP_AGAIN;

- anon_vma = rmap_walk_anon_lock(page, rwc);
+ if (locked) {
+ anon_vma = page_anon_vma(page);
+ /* anon_vma disappear under us? */
+ VM_BUG_ON_PAGE(!anon_vma, page);
+ } else {
+ anon_vma = rmap_walk_anon_lock(page, rwc);
+ }
if (!anon_vma)
return ret;

@@ -1742,7 +1749,9 @@ static int rmap_walk_anon(struct page *page, struct rmap_walk_control *rwc)
if (rwc->done && rwc->done(page))
break;
}
- anon_vma_unlock_read(anon_vma);
+
+ if (!locked)
+ anon_vma_unlock_read(anon_vma);
return ret;
}

@@ -1759,9 +1768,10 @@ static int rmap_walk_anon(struct page *page, struct rmap_walk_control *rwc)
* vm_flags for that VMA. That should be OK, because that vma shouldn't be
* LOCKED.
*/
-static int rmap_walk_file(struct page *page, struct rmap_walk_control *rwc)
+static int rmap_walk_file(struct page *page, struct rmap_walk_control *rwc,
+ bool locked)
{
- struct address_space *mapping = page->mapping;
+ struct address_space *mapping = page_mapping(page);
pgoff_t pgoff;
struct vm_area_struct *vma;
int ret = SWAP_AGAIN;
@@ -1778,7 +1788,8 @@ static int rmap_walk_file(struct page *page, struct rmap_walk_control *rwc)
return ret;

pgoff = page_to_pgoff(page);
- i_mmap_lock_read(mapping);
+ if (!locked)
+ i_mmap_lock_read(mapping);
vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) {
unsigned long address = vma_address(page, vma);

@@ -1795,7 +1806,8 @@ static int rmap_walk_file(struct page *page, struct rmap_walk_control *rwc)
}

done:
- i_mmap_unlock_read(mapping);
+ if (!locked)
+ i_mmap_unlock_read(mapping);
return ret;
}

@@ -1804,9 +1816,20 @@ int rmap_walk(struct page *page, struct rmap_walk_control *rwc)
if (unlikely(PageKsm(page)))
return rmap_walk_ksm(page, rwc);
else if (PageAnon(page))
- return rmap_walk_anon(page, rwc);
+ return rmap_walk_anon(page, rwc, false);
+ else
+ return rmap_walk_file(page, rwc, false);
+}
+
+/* Like rmap_walk, but caller holds relevant rmap lock */
+int rmap_walk_locked(struct page *page, struct rmap_walk_control *rwc)
+{
+ /* no ksm support for now */
+ VM_BUG_ON_PAGE(PageKsm(page), page);
+ if (PageAnon(page))
+ return rmap_walk_anon(page, rwc, true);
else
- return rmap_walk_file(page, rwc);
+ return rmap_walk_file(page, rwc, true);
}

#ifdef CONFIG_HUGETLB_PAGE
--
2.7.0