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Subject[PATCH 1/4] rmap: introduce rmap_walk_locked()
Date
rmap_walk_locked() is the same as rmap_walk(), but caller takes care
about relevant rmap lock. It only supports anonymous pages for now.

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@linux.intel.com>
---
include/linux/rmap.h | 1 +
mm/rmap.c | 25 +++++++++++++++++++++----
2 files changed, 22 insertions(+), 4 deletions(-)

diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index bdf597c4f0be..23a03fbeef61 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -280,6 +280,7 @@ 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 79f3bf047f38..a9cffb784502 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1719,14 +1719,21 @@ 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;

@@ -1746,7 +1753,9 @@ 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;
}

@@ -1808,11 +1817,19 @@ 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);
}

+/* Like rmap_walk, but caller holds relevant rmap lock */
+int rmap_walk_locked(struct page *page, struct rmap_walk_control *rwc)
+{
+ /* only for anon pages for now */
+ VM_BUG_ON_PAGE(!PageAnon(page) || PageKsm(page), page);
+ return rmap_walk_anon(page, rwc, true);
+}
+
#ifdef CONFIG_HUGETLB_PAGE
/*
* The following three functions are for anonymous (private mapped) hugepages.
--
2.7.0
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