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Subject[PATCH -V3] mm: Add PageLayzyFree() helper functions for MADV_FREE
Date
From: Huang Ying <ying.huang@intel.com>

Now PageSwapBacked() is used as the helper function to check whether
pages have been freed lazily via MADV_FREE. This isn't very obvious.
So Dave suggested to add PageLazyFree() family helper functions to
improve the code readability.

Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
Suggested-by: Dave Hansen <dave.hansen@linux.intel.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Hugh Dickins <hughd@google.com>
---
Changelog:

v3:

- Improved comments, Thanks David Hildenbrand!

- Use the helper function in /proc/PID/smaps lazyfree reporting.

v2:

- Avoid code bloat via removing VM_BUG_ON_PAGE(), which doesn't exist
in the original code. Now there is no any text/data/bss size
change.

- Fix one wrong replacement in try_to_unmap_one().

---
fs/proc/task_mmu.c | 2 +-
include/linux/page-flags.h | 25 +++++++++++++++++++++++++
mm/rmap.c | 4 ++--
mm/swap.c | 11 +++--------
mm/vmscan.c | 7 +++----
5 files changed, 34 insertions(+), 15 deletions(-)

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 3ba9ae83bff5..3458d5711e57 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -471,7 +471,7 @@ static void smaps_account(struct mem_size_stats *mss, struct page *page,
*/
if (PageAnon(page)) {
mss->anonymous += size;
- if (!PageSwapBacked(page) && !dirty && !PageDirty(page))
+ if (__PageLazyFree(page) && !dirty && !PageDirty(page))
mss->lazyfree += size;
}

diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 49c2697046b9..bb26f74cbe8e 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -498,6 +498,31 @@ static __always_inline int PageKsm(struct page *page)
TESTPAGEFLAG_FALSE(Ksm)
#endif

+/*
+ * For pages freed lazily via MADV_FREE. Lazyfree pages are clean
+ * anonymous pages. They don't have PG_swapbacked set, to distinguish
+ * them from normal anonymous pages.
+ */
+static __always_inline int __PageLazyFree(struct page *page)
+{
+ return !PageSwapBacked(page);
+}
+
+static __always_inline int PageLazyFree(struct page *page)
+{
+ return PageAnon(page) && __PageLazyFree(page);
+}
+
+static __always_inline void SetPageLazyFree(struct page *page)
+{
+ ClearPageSwapBacked(page);
+}
+
+static __always_inline void ClearPageLazyFree(struct page *page)
+{
+ SetPageSwapBacked(page);
+}
+
u64 stable_page_flags(struct page *page);

static inline int PageUptodate(struct page *page)
diff --git a/mm/rmap.c b/mm/rmap.c
index 1c02adaa233e..6ec96c8e7826 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1609,7 +1609,7 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
}

/* MADV_FREE page check */
- if (!PageSwapBacked(page)) {
+ if (__PageLazyFree(page)) {
if (!PageDirty(page)) {
/* Invalidate as we cleared the pte */
mmu_notifier_invalidate_range(mm,
@@ -1623,7 +1623,7 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
* discarded. Remap the page to page table.
*/
set_pte_at(mm, address, pvmw.pte, pteval);
- SetPageSwapBacked(page);
+ ClearPageLazyFree(page);
ret = false;
page_vma_mapped_walk_done(&pvmw);
break;
diff --git a/mm/swap.c b/mm/swap.c
index c1d3ca80ea10..d83f2cd4cdb8 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -563,7 +563,7 @@ static void lru_deactivate_fn(struct page *page, struct lruvec *lruvec,
static void lru_lazyfree_fn(struct page *page, struct lruvec *lruvec,
void *arg)
{
- if (PageLRU(page) && PageAnon(page) && PageSwapBacked(page) &&
+ if (PageLRU(page) && PageAnon(page) && !__PageLazyFree(page) &&
!PageSwapCache(page) && !PageUnevictable(page)) {
bool active = PageActive(page);

@@ -571,12 +571,7 @@ static void lru_lazyfree_fn(struct page *page, struct lruvec *lruvec,
LRU_INACTIVE_ANON + active);
ClearPageActive(page);
ClearPageReferenced(page);
- /*
- * lazyfree pages are clean anonymous pages. They have
- * SwapBacked flag cleared to distinguish normal anonymous
- * pages
- */
- ClearPageSwapBacked(page);
+ SetPageLazyFree(page);
add_page_to_lru_list(page, lruvec, LRU_INACTIVE_FILE);

__count_vm_events(PGLAZYFREE, hpage_nr_pages(page));
@@ -678,7 +673,7 @@ void deactivate_page(struct page *page)
*/
void mark_page_lazyfree(struct page *page)
{
- if (PageLRU(page) && PageAnon(page) && PageSwapBacked(page) &&
+ if (PageLRU(page) && PageAnon(page) && !__PageLazyFree(page) &&
!PageSwapCache(page) && !PageUnevictable(page)) {
struct pagevec *pvec = &get_cpu_var(lru_lazyfree_pvecs);

diff --git a/mm/vmscan.c b/mm/vmscan.c
index eca49a1c2f68..40bb41ada2d2 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1043,8 +1043,7 @@ static void page_check_dirty_writeback(struct page *page,
* Anonymous pages are not handled by flushers and must be written
* from reclaim context. Do not stall reclaim based on them
*/
- if (!page_is_file_cache(page) ||
- (PageAnon(page) && !PageSwapBacked(page))) {
+ if (!page_is_file_cache(page) || PageLazyFree(page)) {
*dirty = false;
*writeback = false;
return;
@@ -1235,7 +1234,7 @@ static unsigned long shrink_page_list(struct list_head *page_list,
* Try to allocate it some swap space here.
* Lazyfree page could be freed directly
*/
- if (PageAnon(page) && PageSwapBacked(page)) {
+ if (PageAnon(page) && !__PageLazyFree(page)) {
if (!PageSwapCache(page)) {
if (!(sc->gfp_mask & __GFP_IO))
goto keep_locked;
@@ -1411,7 +1410,7 @@ static unsigned long shrink_page_list(struct list_head *page_list,
}
}

- if (PageAnon(page) && !PageSwapBacked(page)) {
+ if (PageLazyFree(page)) {
/* follow __remove_mapping for reference */
if (!page_ref_freeze(page, 1))
goto keep_locked;
--
2.25.0
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