[RFC 00/11] make try_to_unmap simple

[RFC 00/11] make try_to_unmap simple

[Minchan Kim]

Currently, try_to_unmap returns various return value(SWAP_SUCCESS,
SWAP_FAIL, SWAP_AGAIN, SWAP_DIRTY and SWAP_MLOCK). When I look into
that, it's unncessary complicated so this patch aims for cleaning
it up. Change ttu to boolean function so we can remove SWAP_AGAIN,
SWAP_DIRTY, SWAP_MLOCK.

This patchset is based on v4.10-mmots-2017-02-28-17-33.

Minchan Kim (11):
  mm: use SWAP_SUCCESS instead of 0
  mm: remove unncessary ret in page_referenced
  mm: remove SWAP_DIRTY in ttu
  mm: remove SWAP_MLOCK check for SWAP_SUCCESS in ttu
  mm: make the try_to_munlock void function
  mm: remove SWAP_MLOCK in ttu
  mm: remove SWAP_AGAIN in ttu
  mm: make ttu's return boolean
  mm: make rmap_walk void function
  mm: make rmap_one boolean function
  mm: remove SWAP_[SUCCESS|AGAIN|FAIL]

 include/linux/ksm.h  |  5 ++-
 include/linux/rmap.h | 21 ++++--------
 mm/huge_memory.c     |  4 +--
 mm/ksm.c             | 16 ++++-----
 mm/memory-failure.c  | 22 ++++++------
 mm/migrate.c         |  4 +--
 mm/mlock.c           |  6 ++--
 mm/page_idle.c       |  4 +--
 mm/rmap.c            | 97 ++++++++++++++++++++--------------------------------
 mm/vmscan.c          | 26 +++-----------
 10 files changed, 73 insertions(+), 132 deletions(-)

-- 
2.7.4

[RFC 01/11] mm: use SWAP_SUCCESS instead of 0

[Minchan Kim]

SWAP_SUCCESS defined value 0 can be changed always so don't rely on
it. Instead, use explict macro.

Cc: Kirill A. Shutemov <kirill@shutemov.name>
Signed-off-by: Minchan Kim <minchan@kernel.org>
---
 mm/huge_memory.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 092cc5c..fe2ccd4 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2114,7 +2114,7 @@ static void freeze_page(struct page *page)
 		ttu_flags |= TTU_MIGRATION;
 
 	ret = try_to_unmap(page, ttu_flags);
-	VM_BUG_ON_PAGE(ret, page);
+	VM_BUG_ON_PAGE(ret != SWAP_SUCCESS, page);
 }
 
 static void unfreeze_page(struct page *page)
-- 
2.7.4

[RFC 02/11] mm: remove unncessary ret in page_referenced

[Minchan Kim]

Anyone doesn't use ret variable. Remove it.

Signed-off-by: Minchan Kim <minchan@kernel.org>
---
 mm/rmap.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/mm/rmap.c b/mm/rmap.c
index bb45712..8076347 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -805,7 +805,6 @@ int page_referenced(struct page *page,
 		    struct mem_cgroup *memcg,
 		    unsigned long *vm_flags)
 {
-	int ret;
 	int we_locked = 0;
 	struct page_referenced_arg pra = {
 		.mapcount = total_mapcount(page),
@@ -839,7 +838,7 @@ int page_referenced(struct page *page,
 		rwc.invalid_vma = invalid_page_referenced_vma;
 	}
 
-	ret = rmap_walk(page, &rwc);
+	rmap_walk(page, &rwc);
 	*vm_flags = pra.vm_flags;
 
 	if (we_locked)
-- 
2.7.4

[RFC 03/11] mm: remove SWAP_DIRTY in ttu

[Minchan Kim]

If we found lazyfree page is dirty, ttuo can just SetPageSwapBakced
in there like PG_mlocked page and just return with SWAP_FAIL which
is very natural because the page is not swappable right now so that
vmscan can activate it. There is no point to introduce new return
value SWAP_DIRTY in ttu at the moment.

Cc: Shaohua Li <shli@kernel.org>
Signed-off-by: Minchan Kim <minchan@kernel.org>
---
 include/linux/rmap.h | 1 -
 mm/rmap.c            | 4 ++--
 mm/vmscan.c          | 3 ---
 3 files changed, 2 insertions(+), 6 deletions(-)

diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index fee10d7..b556eef 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -298,6 +298,5 @@ static inline int page_mkclean(struct page *page)
 #define SWAP_AGAIN	1
 #define SWAP_FAIL	2
 #define SWAP_MLOCK	3
-#define SWAP_DIRTY	4
 
 #endif	/* _LINUX_RMAP_H */
diff --git a/mm/rmap.c b/mm/rmap.c
index 8076347..3a14013 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1424,7 +1424,8 @@ static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
 			} else if (!PageSwapBacked(page)) {
 				/* dirty MADV_FREE page */
 				set_pte_at(mm, address, pvmw.pte, pteval);
-				ret = SWAP_DIRTY;
+				SetPageSwapBacked(page);
+				ret = SWAP_FAIL;
 				page_vma_mapped_walk_done(&pvmw);
 				break;
 			}
@@ -1494,7 +1495,6 @@ static int page_mapcount_is_zero(struct page *page)
  * SWAP_AGAIN	- we missed a mapping, try again later
  * SWAP_FAIL	- the page is unswappable
  * SWAP_MLOCK	- page is mlocked.
- * SWAP_DIRTY	- page is dirty MADV_FREE page
  */
 int try_to_unmap(struct page *page, enum ttu_flags flags)
 {
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 7aa89e3..91cef05 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1141,9 +1141,6 @@ static unsigned long shrink_page_list(struct list_head *page_list,
 		if (page_mapped(page)) {
 			switch (ret = try_to_unmap(page,
 				ttu_flags | TTU_BATCH_FLUSH)) {
-			case SWAP_DIRTY:
-				SetPageSwapBacked(page);
-				/* fall through */
 			case SWAP_FAIL:
 				nr_unmap_fail++;
 				goto activate_locked;
-- 
2.7.4

[RFC 04/11] mm: remove SWAP_MLOCK check for SWAP_SUCCESS in ttu

[Minchan Kim]

If the page is mapped and rescue in ttuo, page_mapcount(page) == 0 cannot
be true so page_mapcount check in ttu is enough to return SWAP_SUCCESS.
IOW, SWAP_MLOCK check is redundant so remove it.

Signed-off-by: Minchan Kim <minchan@kernel.org>
---
 mm/rmap.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/rmap.c b/mm/rmap.c
index 3a14013..0a48958 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1523,7 +1523,7 @@ int try_to_unmap(struct page *page, enum ttu_flags flags)
 	else
 		ret = rmap_walk(page, &rwc);
 
-	if (ret != SWAP_MLOCK && !page_mapcount(page))
+	if (!page_mapcount(page))
 		ret = SWAP_SUCCESS;
 	return ret;
 }
-- 
2.7.4

[RFC 05/11] mm: make the try_to_munlock void function

[Minchan Kim]

try_to_munlock returns SWAP_MLOCK if the one of VMAs mapped
the page has VM_LOCKED flag. In that time, VM set PG_mlocked to
the page if the page is not pte-mapped THP which cannot be
mlocked, either.

With that, __munlock_isolated_page can use PageMlocked to check
whether try_to_munlock is successful or not without relying on
try_to_munlock's retval. It helps to make ttu/ttuo simple with
upcoming patches.

Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Minchan Kim <minchan@kernel.org>
---
 include/linux/rmap.h |  2 +-
 mm/mlock.c           |  6 ++----
 mm/rmap.c            | 16 ++++------------
 3 files changed, 7 insertions(+), 17 deletions(-)

diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index b556eef..1b0cd4c 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -235,7 +235,7 @@ int page_mkclean(struct page *);
  * called in munlock()/munmap() path to check for other vmas holding
  * the page mlocked.
  */
-int try_to_munlock(struct page *);
+void try_to_munlock(struct page *);
 
 void remove_migration_ptes(struct page *old, struct page *new, bool locked);
 
diff --git a/mm/mlock.c b/mm/mlock.c
index cdbed8a..d34a540 100644
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -122,17 +122,15 @@ static bool __munlock_isolate_lru_page(struct page *page, bool getpage)
  */
 static void __munlock_isolated_page(struct page *page)
 {
-	int ret = SWAP_AGAIN;
-
 	/*
 	 * Optimization: if the page was mapped just once, that's our mapping
 	 * and we don't need to check all the other vmas.
 	 */
 	if (page_mapcount(page) > 1)
-		ret = try_to_munlock(page);
+		try_to_munlock(page);
 
 	/* Did try_to_unlock() succeed or punt? */
-	if (ret != SWAP_MLOCK)
+	if (!PageMlocked(page))
 		count_vm_event(UNEVICTABLE_PGMUNLOCKED);
 
 	putback_lru_page(page);
diff --git a/mm/rmap.c b/mm/rmap.c
index 0a48958..61ae694 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1540,18 +1540,10 @@ static int page_not_mapped(struct page *page)
  * Called from munlock code.  Checks all of the VMAs mapping the page
  * to make sure nobody else has this page mlocked. The page will be
  * returned with PG_mlocked cleared if no other vmas have it mlocked.
- *
- * Return values are:
- *
- * SWAP_AGAIN	- no vma is holding page mlocked, or,
- * SWAP_AGAIN	- page mapped in mlocked vma -- couldn't acquire mmap sem
- * SWAP_FAIL	- page cannot be located at present
- * SWAP_MLOCK	- page is now mlocked.
  */
-int try_to_munlock(struct page *page)
-{
-	int ret;
 
+void try_to_munlock(struct page *page)
+{
 	struct rmap_walk_control rwc = {
 		.rmap_one = try_to_unmap_one,
 		.arg = (void *)TTU_MUNLOCK,
@@ -1561,9 +1553,9 @@ int try_to_munlock(struct page *page)
 	};
 
 	VM_BUG_ON_PAGE(!PageLocked(page) || PageLRU(page), page);
+	VM_BUG_ON_PAGE(PageMlocked(page), page);
 
-	ret = rmap_walk(page, &rwc);
-	return ret;
+	rmap_walk(page, &rwc);
 }
 
 void __put_anon_vma(struct anon_vma *anon_vma)
-- 
2.7.4

[RFC 06/11] mm: remove SWAP_MLOCK in ttu

[Minchan Kim]

ttu don't need to return SWAP_MLOCK. Instead, just return SWAP_FAIL
because it means the page is not-swappable so it should move to
another LRU list(active or unevictable). putback friends will
move it to right list depending on the page's LRU flag.

A side effect is shrink_page_list accounts unevictable list movement
by PGACTIVATE but I don't think it corrupts something severe.

Signed-off-by: Minchan Kim <minchan@kernel.org>
---
 include/linux/rmap.h |  1 -
 mm/rmap.c            |  3 +--
 mm/vmscan.c          | 14 +++-----------
 3 files changed, 4 insertions(+), 14 deletions(-)

diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index 1b0cd4c..3630d4d 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -297,6 +297,5 @@ static inline int page_mkclean(struct page *page)
 #define SWAP_SUCCESS	0
 #define SWAP_AGAIN	1
 #define SWAP_FAIL	2
-#define SWAP_MLOCK	3
 
 #endif	/* _LINUX_RMAP_H */
diff --git a/mm/rmap.c b/mm/rmap.c
index 61ae694..47898a1 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1328,7 +1328,7 @@ static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
 					 */
 					mlock_vma_page(page);
 				}
-				ret = SWAP_MLOCK;
+				ret = SWAP_FAIL;
 				page_vma_mapped_walk_done(&pvmw);
 				break;
 			}
@@ -1494,7 +1494,6 @@ static int page_mapcount_is_zero(struct page *page)
  * SWAP_SUCCESS	- we succeeded in removing all mappings
  * SWAP_AGAIN	- we missed a mapping, try again later
  * SWAP_FAIL	- the page is unswappable
- * SWAP_MLOCK	- page is mlocked.
  */
 int try_to_unmap(struct page *page, enum ttu_flags flags)
 {
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 91cef05..3cdd270b 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -981,7 +981,7 @@ static unsigned long shrink_page_list(struct list_head *page_list,
 		sc->nr_scanned++;
 
 		if (unlikely(!page_evictable(page)))
-			goto cull_mlocked;
+			goto activate_locked;
 
 		if (!sc->may_unmap && page_mapped(page))
 			goto keep_locked;
@@ -1146,8 +1146,6 @@ static unsigned long shrink_page_list(struct list_head *page_list,
 				goto activate_locked;
 			case SWAP_AGAIN:
 				goto keep_locked;
-			case SWAP_MLOCK:
-				goto cull_mlocked;
 			case SWAP_SUCCESS:
 				; /* try to free the page below */
 			}
@@ -1289,16 +1287,10 @@ static unsigned long shrink_page_list(struct list_head *page_list,
 		list_add(&page->lru, &free_pages);
 		continue;
 
-cull_mlocked:
-		if (PageSwapCache(page))
-			try_to_free_swap(page);
-		unlock_page(page);
-		list_add(&page->lru, &ret_pages);
-		continue;
-
 activate_locked:
 		/* Not a candidate for swapping, so reclaim swap space. */
-		if (PageSwapCache(page) && mem_cgroup_swap_full(page))
+		if (PageSwapCache(page) && (mem_cgroup_swap_full(page) ||
+						PageMlocked(page)))
 			try_to_free_swap(page);
 		VM_BUG_ON_PAGE(PageActive(page), page);
 		SetPageActive(page);
-- 
2.7.4

[RFC 07/11] mm: remove SWAP_AGAIN in ttu

[Minchan Kim]

In 2002, [1] introduced SWAP_AGAIN.
At that time, ttuo used spin_trylock(&mm->page_table_lock) so it's
really easy to contend and fail to hold a lock so SWAP_AGAIN to keep
LRU status makes sense.

However, now we changed it to mutex-based lock and be able to block
without skip pte so there is a few of small window to return
SWAP_AGAIN so remove SWAP_AGAIN and just return SWAP_FAIL.

[1] c48c43e, minimal rmap
Signed-off-by: Minchan Kim <minchan@kernel.org>
---
 mm/rmap.c   | 11 +++--------
 mm/vmscan.c |  2 --
 2 files changed, 3 insertions(+), 10 deletions(-)

diff --git a/mm/rmap.c b/mm/rmap.c
index 47898a1..da18f21 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1492,13 +1492,10 @@ static int page_mapcount_is_zero(struct page *page)
  * Return values are:
  *
  * SWAP_SUCCESS	- we succeeded in removing all mappings
- * SWAP_AGAIN	- we missed a mapping, try again later
  * SWAP_FAIL	- the page is unswappable
  */
 int try_to_unmap(struct page *page, enum ttu_flags flags)
 {
-	int ret;
-
 	struct rmap_walk_control rwc = {
 		.rmap_one = try_to_unmap_one,
 		.arg = (void *)flags,
@@ -1518,13 +1515,11 @@ int try_to_unmap(struct page *page, enum ttu_flags flags)
 		rwc.invalid_vma = invalid_migration_vma;
 
 	if (flags & TTU_RMAP_LOCKED)
-		ret = rmap_walk_locked(page, &rwc);
+		rmap_walk_locked(page, &rwc);
 	else
-		ret = rmap_walk(page, &rwc);
+		rmap_walk(page, &rwc);
 
-	if (!page_mapcount(page))
-		ret = SWAP_SUCCESS;
-	return ret;
+	return !page_mapcount(page) ? SWAP_SUCCESS: SWAP_FAIL;
 }
 
 static int page_not_mapped(struct page *page)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 3cdd270b..170c61f 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1144,8 +1144,6 @@ static unsigned long shrink_page_list(struct list_head *page_list,
 			case SWAP_FAIL:
 				nr_unmap_fail++;
 				goto activate_locked;
-			case SWAP_AGAIN:
-				goto keep_locked;
 			case SWAP_SUCCESS:
 				; /* try to free the page below */
 			}
-- 
2.7.4

[RFC 08/11] mm: make ttu's return boolean

[Minchan Kim]

try_to_unmap returns SWAP_SUCCESS or SWAP_FAIL so it's suitable for
boolean return. This patch changes it.

Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Signed-off-by: Minchan Kim <minchan@kernel.org>
---
 include/linux/rmap.h |  4 ++--
 mm/huge_memory.c     |  4 ++--
 mm/memory-failure.c  | 22 ++++++++++------------
 mm/rmap.c            |  8 +++-----
 mm/vmscan.c          |  7 +------
 5 files changed, 18 insertions(+), 27 deletions(-)

diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index 3630d4d..6028c38 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -191,7 +191,7 @@ static inline void page_dup_rmap(struct page *page, bool compound)
 int page_referenced(struct page *, int is_locked,
 			struct mem_cgroup *memcg, unsigned long *vm_flags);
 
-int try_to_unmap(struct page *, enum ttu_flags flags);
+bool try_to_unmap(struct page *, enum ttu_flags flags);
 
 /* Avoid racy checks */
 #define PVMW_SYNC		(1 << 0)
@@ -281,7 +281,7 @@ static inline int page_referenced(struct page *page, int is_locked,
 	return 0;
 }
 
-#define try_to_unmap(page, refs) SWAP_FAIL
+#define try_to_unmap(page, refs) false
 
 static inline int page_mkclean(struct page *page)
 {
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index fe2ccd4..79ea769 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2106,7 +2106,7 @@ static void freeze_page(struct page *page)
 {
 	enum ttu_flags ttu_flags = TTU_IGNORE_MLOCK | TTU_IGNORE_ACCESS |
 		TTU_RMAP_LOCKED | TTU_SPLIT_HUGE_PMD;
-	int ret;
+	bool ret;
 
 	VM_BUG_ON_PAGE(!PageHead(page), page);
 
@@ -2114,7 +2114,7 @@ static void freeze_page(struct page *page)
 		ttu_flags |= TTU_MIGRATION;
 
 	ret = try_to_unmap(page, ttu_flags);
-	VM_BUG_ON_PAGE(ret != SWAP_SUCCESS, page);
+	VM_BUG_ON_PAGE(!ret, page);
 }
 
 static void unfreeze_page(struct page *page)
diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index b78d080..75fcbd8 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -321,7 +321,7 @@ static void add_to_kill(struct task_struct *tsk, struct page *p,
  * wrong earlier.
  */
 static void kill_procs(struct list_head *to_kill, int forcekill, int trapno,
-			  int fail, struct page *page, unsigned long pfn,
+			  bool fail, struct page *page, unsigned long pfn,
 			  int flags)
 {
 	struct to_kill *tk, *next;
@@ -903,13 +903,13 @@ EXPORT_SYMBOL_GPL(get_hwpoison_page);
  * Do all that is necessary to remove user space mappings. Unmap
  * the pages and send SIGBUS to the processes if the data was dirty.
  */
-static int hwpoison_user_mappings(struct page *p, unsigned long pfn,
+static bool hwpoison_user_mappings(struct page *p, unsigned long pfn,
 				  int trapno, int flags, struct page **hpagep)
 {
 	enum ttu_flags ttu = TTU_IGNORE_MLOCK | TTU_IGNORE_ACCESS;
 	struct address_space *mapping;
 	LIST_HEAD(tokill);
-	int ret;
+	bool ret;
 	int kill = 1, forcekill;
 	struct page *hpage = *hpagep;
 
@@ -918,20 +918,20 @@ static int hwpoison_user_mappings(struct page *p, unsigned long pfn,
 	 * other types of pages.
 	 */
 	if (PageReserved(p) || PageSlab(p))
-		return SWAP_SUCCESS;
+		return true;
 	if (!(PageLRU(hpage) || PageHuge(p)))
-		return SWAP_SUCCESS;
+		return true;
 
 	/*
 	 * This check implies we don't kill processes if their pages
 	 * are in the swap cache early. Those are always late kills.
 	 */
 	if (!page_mapped(hpage))
-		return SWAP_SUCCESS;
+		return true;
 
 	if (PageKsm(p)) {
 		pr_err("Memory failure: %#lx: can't handle KSM pages.\n", pfn);
-		return SWAP_FAIL;
+		return false;
 	}
 
 	if (PageSwapCache(p)) {
@@ -971,7 +971,7 @@ static int hwpoison_user_mappings(struct page *p, unsigned long pfn,
 		collect_procs(hpage, &tokill, flags & MF_ACTION_REQUIRED);
 
 	ret = try_to_unmap(hpage, ttu);
-	if (ret != SWAP_SUCCESS)
+	if (!ret)
 		pr_err("Memory failure: %#lx: failed to unmap page (mapcount=%d)\n",
 		       pfn, page_mapcount(hpage));
 
@@ -986,8 +986,7 @@ static int hwpoison_user_mappings(struct page *p, unsigned long pfn,
 	 * any accesses to the poisoned memory.
 	 */
 	forcekill = PageDirty(hpage) || (flags & MF_MUST_KILL);
-	kill_procs(&tokill, forcekill, trapno,
-		      ret != SWAP_SUCCESS, p, pfn, flags);
+	kill_procs(&tokill, forcekill, trapno, !ret , p, pfn, flags);
 
 	return ret;
 }
@@ -1229,8 +1228,7 @@ int memory_failure(unsigned long pfn, int trapno, int flags)
 	 * When the raw error page is thp tail page, hpage points to the raw
 	 * page after thp split.
 	 */
-	if (hwpoison_user_mappings(p, pfn, trapno, flags, &hpage)
-	    != SWAP_SUCCESS) {
+	if (!hwpoison_user_mappings(p, pfn, trapno, flags, &hpage)) {
 		action_result(pfn, MF_MSG_UNMAP_FAILED, MF_IGNORED);
 		res = -EBUSY;
 		goto out;
diff --git a/mm/rmap.c b/mm/rmap.c
index da18f21..01f7832 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1489,12 +1489,10 @@ static int page_mapcount_is_zero(struct page *page)
  *
  * Tries to remove all the page table entries which are mapping this
  * page, used in the pageout path.  Caller must hold the page lock.
- * Return values are:
  *
- * SWAP_SUCCESS	- we succeeded in removing all mappings
- * SWAP_FAIL	- the page is unswappable
+ * If unmap is successful, return true. Otherwise, false.
  */
-int try_to_unmap(struct page *page, enum ttu_flags flags)
+bool try_to_unmap(struct page *page, enum ttu_flags flags)
 {
 	struct rmap_walk_control rwc = {
 		.rmap_one = try_to_unmap_one,
@@ -1519,7 +1517,7 @@ int try_to_unmap(struct page *page, enum ttu_flags flags)
 	else
 		rmap_walk(page, &rwc);
 
-	return !page_mapcount(page) ? SWAP_SUCCESS: SWAP_FAIL;
+	return !page_mapcount(page) ? true: false;
 }
 
 static int page_not_mapped(struct page *page)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 170c61f..e4b74f1 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -966,7 +966,6 @@ static unsigned long shrink_page_list(struct list_head *page_list,
 		int may_enter_fs;
 		enum page_references references = PAGEREF_RECLAIM_CLEAN;
 		bool dirty, writeback;
-		int ret = SWAP_SUCCESS;
 
 		cond_resched();
 
@@ -1139,13 +1138,9 @@ static unsigned long shrink_page_list(struct list_head *page_list,
 		 * processes. Try to unmap it here.
 		 */
 		if (page_mapped(page)) {
-			switch (ret = try_to_unmap(page,
-				ttu_flags | TTU_BATCH_FLUSH)) {
-			case SWAP_FAIL:
+			if (!try_to_unmap(page, ttu_flags | TTU_BATCH_FLUSH)) {
 				nr_unmap_fail++;
 				goto activate_locked;
-			case SWAP_SUCCESS:
-				; /* try to free the page below */
 			}
 		}
 
-- 
2.7.4

[RFC 09/11] mm: make rmap_walk void function

[Minchan Kim]

There is no user of return value from rmap_walk friend so this
patch makes them void function.

Signed-off-by: Minchan Kim <minchan@kernel.org>
---
 include/linux/ksm.h  |  5 ++---
 include/linux/rmap.h |  4 ++--
 mm/ksm.c             | 16 ++++++----------
 mm/rmap.c            | 32 +++++++++++++-------------------
 4 files changed, 23 insertions(+), 34 deletions(-)

diff --git a/include/linux/ksm.h b/include/linux/ksm.h
index 481c8c4..317ad0b 100644
--- a/include/linux/ksm.h
+++ b/include/linux/ksm.h
@@ -60,7 +60,7 @@ static inline void set_page_stable_node(struct page *page,
 struct page *ksm_might_need_to_copy(struct page *page,
 			struct vm_area_struct *vma, unsigned long address);
 
-int rmap_walk_ksm(struct page *page, struct rmap_walk_control *rwc);
+void rmap_walk_ksm(struct page *page, struct rmap_walk_control *rwc);
 void ksm_migrate_page(struct page *newpage, struct page *oldpage);
 
 #else  /* !CONFIG_KSM */
@@ -93,10 +93,9 @@ static inline int page_referenced_ksm(struct page *page,
 	return 0;
 }
 
-static inline int rmap_walk_ksm(struct page *page,
+static inline void rmap_walk_ksm(struct page *page,
 			struct rmap_walk_control *rwc)
 {
-	return 0;
 }
 
 static inline void ksm_migrate_page(struct page *newpage, struct page *oldpage)
diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index 6028c38..1d7d457c 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -264,8 +264,8 @@ struct rmap_walk_control {
 	bool (*invalid_vma)(struct vm_area_struct *vma, void *arg);
 };
 
-int rmap_walk(struct page *page, struct rmap_walk_control *rwc);
-int rmap_walk_locked(struct page *page, struct rmap_walk_control *rwc);
+void rmap_walk(struct page *page, struct rmap_walk_control *rwc);
+void rmap_walk_locked(struct page *page, struct rmap_walk_control *rwc);
 
 #else	/* !CONFIG_MMU */
 
diff --git a/mm/ksm.c b/mm/ksm.c
index 520e4c3..68f8820 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -1931,11 +1931,10 @@ struct page *ksm_might_need_to_copy(struct page *page,
 	return new_page;
 }
 
-int rmap_walk_ksm(struct page *page, struct rmap_walk_control *rwc)
+void rmap_walk_ksm(struct page *page, struct rmap_walk_control *rwc)
 {
 	struct stable_node *stable_node;
 	struct rmap_item *rmap_item;
-	int ret = SWAP_AGAIN;
 	int search_new_forks = 0;
 
 	VM_BUG_ON_PAGE(!PageKsm(page), page);
@@ -1948,7 +1947,7 @@ int rmap_walk_ksm(struct page *page, struct rmap_walk_control *rwc)
 
 	stable_node = page_stable_node(page);
 	if (!stable_node)
-		return ret;
+		return;
 again:
 	hlist_for_each_entry(rmap_item, &stable_node->hlist, hlist) {
 		struct anon_vma *anon_vma = rmap_item->anon_vma;
@@ -1976,23 +1975,20 @@ int rmap_walk_ksm(struct page *page, struct rmap_walk_control *rwc)
 			if (rwc->invalid_vma && rwc->invalid_vma(vma, rwc->arg))
 				continue;
 
-			ret = rwc->rmap_one(page, vma,
-					rmap_item->address, rwc->arg);
-			if (ret != SWAP_AGAIN) {
+			if (SWAP_AGAIN != rwc->rmap_one(page, vma,
+					rmap_item->address, rwc->arg)) {
 				anon_vma_unlock_read(anon_vma);
-				goto out;
+				return;
 			}
 			if (rwc->done && rwc->done(page)) {
 				anon_vma_unlock_read(anon_vma);
-				goto out;
+				return;
 			}
 		}
 		anon_vma_unlock_read(anon_vma);
 	}
 	if (!search_new_forks++)
 		goto again;
-out:
-	return ret;
 }
 
 #ifdef CONFIG_MIGRATION
diff --git a/mm/rmap.c b/mm/rmap.c
index 01f7832..08e4f81 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1595,13 +1595,12 @@ 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 void rmap_walk_anon(struct page *page, struct rmap_walk_control *rwc,
 		bool locked)
 {
 	struct anon_vma *anon_vma;
 	pgoff_t pgoff_start, pgoff_end;
 	struct anon_vma_chain *avc;
-	int ret = SWAP_AGAIN;
 
 	if (locked) {
 		anon_vma = page_anon_vma(page);
@@ -1611,7 +1610,7 @@ static int rmap_walk_anon(struct page *page, struct rmap_walk_control *rwc,
 		anon_vma = rmap_walk_anon_lock(page, rwc);
 	}
 	if (!anon_vma)
-		return ret;
+		return;
 
 	pgoff_start = page_to_pgoff(page);
 	pgoff_end = pgoff_start + hpage_nr_pages(page) - 1;
@@ -1625,8 +1624,7 @@ static int rmap_walk_anon(struct page *page, struct rmap_walk_control *rwc,
 		if (rwc->invalid_vma && rwc->invalid_vma(vma, rwc->arg))
 			continue;
 
-		ret = rwc->rmap_one(page, vma, address, rwc->arg);
-		if (ret != SWAP_AGAIN)
+		if (SWAP_AGAIN != rwc->rmap_one(page, vma, address, rwc->arg))
 			break;
 		if (rwc->done && rwc->done(page))
 			break;
@@ -1634,7 +1632,6 @@ static int rmap_walk_anon(struct page *page, struct rmap_walk_control *rwc,
 
 	if (!locked)
 		anon_vma_unlock_read(anon_vma);
-	return ret;
 }
 
 /*
@@ -1650,13 +1647,12 @@ 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 void rmap_walk_file(struct page *page, struct rmap_walk_control *rwc,
 		bool locked)
 {
 	struct address_space *mapping = page_mapping(page);
 	pgoff_t pgoff_start, pgoff_end;
 	struct vm_area_struct *vma;
-	int ret = SWAP_AGAIN;
 
 	/*
 	 * The page lock not only makes sure that page->mapping cannot
@@ -1667,7 +1663,7 @@ static int rmap_walk_file(struct page *page, struct rmap_walk_control *rwc,
 	VM_BUG_ON_PAGE(!PageLocked(page), page);
 
 	if (!mapping)
-		return ret;
+		return;
 
 	pgoff_start = page_to_pgoff(page);
 	pgoff_end = pgoff_start + hpage_nr_pages(page) - 1;
@@ -1682,8 +1678,7 @@ static int rmap_walk_file(struct page *page, struct rmap_walk_control *rwc,
 		if (rwc->invalid_vma && rwc->invalid_vma(vma, rwc->arg))
 			continue;
 
-		ret = rwc->rmap_one(page, vma, address, rwc->arg);
-		if (ret != SWAP_AGAIN)
+		if (SWAP_AGAIN != rwc->rmap_one(page, vma, address, rwc->arg))
 			goto done;
 		if (rwc->done && rwc->done(page))
 			goto done;
@@ -1692,28 +1687,27 @@ static int rmap_walk_file(struct page *page, struct rmap_walk_control *rwc,
 done:
 	if (!locked)
 		i_mmap_unlock_read(mapping);
-	return ret;
 }
 
-int rmap_walk(struct page *page, struct rmap_walk_control *rwc)
+void rmap_walk(struct page *page, struct rmap_walk_control *rwc)
 {
 	if (unlikely(PageKsm(page)))
-		return rmap_walk_ksm(page, rwc);
+		rmap_walk_ksm(page, rwc);
 	else if (PageAnon(page))
-		return rmap_walk_anon(page, rwc, false);
+		rmap_walk_anon(page, rwc, false);
 	else
-		return rmap_walk_file(page, rwc, false);
+		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)
+void 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);
+		rmap_walk_anon(page, rwc, true);
 	else
-		return rmap_walk_file(page, rwc, true);
+		rmap_walk_file(page, rwc, true);
 }
 
 #ifdef CONFIG_HUGETLB_PAGE
-- 
2.7.4

[RFC 10/11] mm: make rmap_one boolean function

[Minchan Kim]

rmap_one's return value controls whether rmap_work should contine to
scan other ptes or not so it's target for changing to boolean.
Return true if the scan should be continued. Otherwise, return false
to stop the scanning.

This patch makes rmap_one's return value to boolean.

Signed-off-by: Minchan Kim <minchan@kernel.org>
---
 include/linux/rmap.h |  2 +-
 mm/ksm.c             |  2 +-
 mm/migrate.c         |  4 ++--
 mm/page_idle.c       |  4 ++--
 mm/rmap.c            | 30 +++++++++++++++---------------
 5 files changed, 21 insertions(+), 21 deletions(-)

diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index 1d7d457c..59d7dd7 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -257,7 +257,7 @@ int page_mapped_in_vma(struct page *page, struct vm_area_struct *vma);
  */
 struct rmap_walk_control {
 	void *arg;
-	int (*rmap_one)(struct page *page, struct vm_area_struct *vma,
+	bool (*rmap_one)(struct page *page, struct vm_area_struct *vma,
 					unsigned long addr, void *arg);
 	int (*done)(struct page *page);
 	struct anon_vma *(*anon_lock)(struct page *page);
diff --git a/mm/ksm.c b/mm/ksm.c
index 68f8820..f764afb 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -1975,7 +1975,7 @@ void rmap_walk_ksm(struct page *page, struct rmap_walk_control *rwc)
 			if (rwc->invalid_vma && rwc->invalid_vma(vma, rwc->arg))
 				continue;
 
-			if (SWAP_AGAIN != rwc->rmap_one(page, vma,
+			if (!rwc->rmap_one(page, vma,
 					rmap_item->address, rwc->arg)) {
 				anon_vma_unlock_read(anon_vma);
 				return;
diff --git a/mm/migrate.c b/mm/migrate.c
index cda4c27..22daaea 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -193,7 +193,7 @@ void putback_movable_pages(struct list_head *l)
 /*
  * Restore a potential migration pte to a working pte entry
  */
-static int remove_migration_pte(struct page *page, struct vm_area_struct *vma,
+static bool remove_migration_pte(struct page *page, struct vm_area_struct *vma,
 				 unsigned long addr, void *old)
 {
 	struct page_vma_mapped_walk pvmw = {
@@ -249,7 +249,7 @@ static int remove_migration_pte(struct page *page, struct vm_area_struct *vma,
 		update_mmu_cache(vma, pvmw.address, pvmw.pte);
 	}
 
-	return SWAP_AGAIN;
+	return true;
 }
 
 /*
diff --git a/mm/page_idle.c b/mm/page_idle.c
index b0ee56c..1b0f48c 100644
--- a/mm/page_idle.c
+++ b/mm/page_idle.c
@@ -50,7 +50,7 @@ static struct page *page_idle_get_page(unsigned long pfn)
 	return page;
 }
 
-static int page_idle_clear_pte_refs_one(struct page *page,
+static bool page_idle_clear_pte_refs_one(struct page *page,
 					struct vm_area_struct *vma,
 					unsigned long addr, void *arg)
 {
@@ -84,7 +84,7 @@ static int page_idle_clear_pte_refs_one(struct page *page,
 		 */
 		set_page_young(page);
 	}
-	return SWAP_AGAIN;
+	return true;
 }
 
 static void page_idle_clear_pte_refs(struct page *page)
diff --git a/mm/rmap.c b/mm/rmap.c
index 08e4f81..60adedb 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -717,7 +717,7 @@ struct page_referenced_arg {
 /*
  * arg: page_referenced_arg will be passed
  */
-static int page_referenced_one(struct page *page, struct vm_area_struct *vma,
+static bool page_referenced_one(struct page *page, struct vm_area_struct *vma,
 			unsigned long address, void *arg)
 {
 	struct page_referenced_arg *pra = arg;
@@ -734,7 +734,7 @@ static int page_referenced_one(struct page *page, struct vm_area_struct *vma,
 		if (vma->vm_flags & VM_LOCKED) {
 			page_vma_mapped_walk_done(&pvmw);
 			pra->vm_flags |= VM_LOCKED;
-			return SWAP_FAIL; /* To break the loop */
+			return false; /* To break the loop */
 		}
 
 		if (pvmw.pte) {
@@ -774,9 +774,9 @@ static int page_referenced_one(struct page *page, struct vm_area_struct *vma,
 	}
 
 	if (!pra->mapcount)
-		return SWAP_SUCCESS; /* To break the loop */
+		return false; /* To break the loop */
 
-	return SWAP_AGAIN;
+	return true;
 }
 
 static bool invalid_page_referenced_vma(struct vm_area_struct *vma, void *arg)
@@ -847,7 +847,7 @@ int page_referenced(struct page *page,
 	return pra.referenced;
 }
 
-static int page_mkclean_one(struct page *page, struct vm_area_struct *vma,
+static bool page_mkclean_one(struct page *page, struct vm_area_struct *vma,
 			    unsigned long address, void *arg)
 {
 	struct page_vma_mapped_walk pvmw = {
@@ -900,7 +900,7 @@ static int page_mkclean_one(struct page *page, struct vm_area_struct *vma,
 		}
 	}
 
-	return SWAP_AGAIN;
+	return true;
 }
 
 static bool invalid_mkclean_vma(struct vm_area_struct *vma, void *arg)
@@ -1283,7 +1283,7 @@ void page_remove_rmap(struct page *page, bool compound)
 /*
  * @arg: enum ttu_flags will be passed to this argument
  */
-static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
+static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
 		     unsigned long address, void *arg)
 {
 	struct mm_struct *mm = vma->vm_mm;
@@ -1294,12 +1294,12 @@ static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
 	};
 	pte_t pteval;
 	struct page *subpage;
-	int ret = SWAP_AGAIN;
+	bool ret = true;
 	enum ttu_flags flags = (enum ttu_flags)arg;
 
 	/* munlock has nothing to gain from examining un-locked vmas */
 	if ((flags & TTU_MUNLOCK) && !(vma->vm_flags & VM_LOCKED))
-		return SWAP_AGAIN;
+		return true;
 
 	if (flags & TTU_SPLIT_HUGE_PMD) {
 		split_huge_pmd_address(vma, address,
@@ -1328,7 +1328,7 @@ static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
 					 */
 					mlock_vma_page(page);
 				}
-				ret = SWAP_FAIL;
+				ret = false;
 				page_vma_mapped_walk_done(&pvmw);
 				break;
 			}
@@ -1339,7 +1339,7 @@ static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
 		if (!(flags & TTU_IGNORE_ACCESS)) {
 			if (ptep_clear_flush_young_notify(vma, address,
 						pvmw.pte)) {
-				ret = SWAP_FAIL;
+				ret = false;
 				page_vma_mapped_walk_done(&pvmw);
 				break;
 			}
@@ -1425,14 +1425,14 @@ static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
 				/* dirty MADV_FREE page */
 				set_pte_at(mm, address, pvmw.pte, pteval);
 				SetPageSwapBacked(page);
-				ret = SWAP_FAIL;
+				ret = false;
 				page_vma_mapped_walk_done(&pvmw);
 				break;
 			}
 
 			if (swap_duplicate(entry) < 0) {
 				set_pte_at(mm, address, pvmw.pte, pteval);
-				ret = SWAP_FAIL;
+				ret = false;
 				page_vma_mapped_walk_done(&pvmw);
 				break;
 			}
@@ -1624,7 +1624,7 @@ static void rmap_walk_anon(struct page *page, struct rmap_walk_control *rwc,
 		if (rwc->invalid_vma && rwc->invalid_vma(vma, rwc->arg))
 			continue;
 
-		if (SWAP_AGAIN != rwc->rmap_one(page, vma, address, rwc->arg))
+		if (!rwc->rmap_one(page, vma, address, rwc->arg))
 			break;
 		if (rwc->done && rwc->done(page))
 			break;
@@ -1678,7 +1678,7 @@ static void rmap_walk_file(struct page *page, struct rmap_walk_control *rwc,
 		if (rwc->invalid_vma && rwc->invalid_vma(vma, rwc->arg))
 			continue;
 
-		if (SWAP_AGAIN != rwc->rmap_one(page, vma, address, rwc->arg))
+		if (!rwc->rmap_one(page, vma, address, rwc->arg))
 			goto done;
 		if (rwc->done && rwc->done(page))
 			goto done;
-- 
2.7.4

[RFC 11/11] mm: remove SWAP_[SUCCESS|AGAIN|FAIL]

[Minchan Kim]

There is no user for it. Remove it.

Signed-off-by: Minchan Kim <minchan@kernel.org>
---
 include/linux/rmap.h | 7 -------
 1 file changed, 7 deletions(-)

diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index 59d7dd7..5d6788f 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -291,11 +291,4 @@ static inline int page_mkclean(struct page *page)
 
 #endif	/* CONFIG_MMU */
 
-/*
- * Return values of try_to_unmap
- */
-#define SWAP_SUCCESS	0
-#define SWAP_AGAIN	1
-#define SWAP_FAIL	2
-
 #endif	/* _LINUX_RMAP_H */
-- 
2.7.4

Re: [RFC 03/11] mm: remove SWAP_DIRTY in ttu

[Hillf Danton]

On March 02, 2017 2:39 PM Minchan Kim wrote: 
> @@ -1424,7 +1424,8 @@ static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
>  			} else if (!PageSwapBacked(page)) {
>  				/* dirty MADV_FREE page */

Nit: enrich the comment please.
>  				set_pte_at(mm, address, pvmw.pte, pteval);
> -				ret = SWAP_DIRTY;
> +				SetPageSwapBacked(page);
> +				ret = SWAP_FAIL;
>  				page_vma_mapped_walk_done(&pvmw);
>  				break;
>  			}

Re: [RFC 00/11] make try_to_unmap simple

[Anshuman Khandual]

On 03/02/2017 12:09 PM, Minchan Kim wrote:
> Currently, try_to_unmap returns various return value(SWAP_SUCCESS,
> SWAP_FAIL, SWAP_AGAIN, SWAP_DIRTY and SWAP_MLOCK). When I look into
> that, it's unncessary complicated so this patch aims for cleaning
> it up. Change ttu to boolean function so we can remove SWAP_AGAIN,
> SWAP_DIRTY, SWAP_MLOCK.

It may be a trivial question but apart from being a cleanup does it
help in improving it's callers some way ? Any other benefits ?

Re: [RFC 01/11] mm: use SWAP_SUCCESS instead of 0

[Anshuman Khandual]

On 03/02/2017 12:09 PM, Minchan Kim wrote:
> SWAP_SUCCESS defined value 0 can be changed always so don't rely on
> it. Instead, use explict macro.

Right. But should not we move the changes to the callers last in the
patch series after doing the cleanup to the try_to_unmap() function
as intended first.

> > Cc: Kirill A. Shutemov <kirill@shutemov.name>
> Signed-off-by: Minchan Kim <minchan@kernel.org>
> ---
>  mm/huge_memory.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 092cc5c..fe2ccd4 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -2114,7 +2114,7 @@ static void freeze_page(struct page *page)
>  		ttu_flags |= TTU_MIGRATION;
>  
>  	ret = try_to_unmap(page, ttu_flags);
> -	VM_BUG_ON_PAGE(ret, page);
> +	VM_BUG_ON_PAGE(ret != SWAP_SUCCESS, page);
>  }
>  
>  static void unfreeze_page(struct page *page)
> 

Re: [RFC 02/11] mm: remove unncessary ret in page_referenced

[Anshuman Khandual]

On 03/02/2017 12:09 PM, Minchan Kim wrote:
> Anyone doesn't use ret variable. Remove it.
> 

This change is correct. But not sure how this is related to
try_to_unmap() clean up though.


> Signed-off-by: Minchan Kim <minchan@kernel.org>
> ---
>  mm/rmap.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/mm/rmap.c b/mm/rmap.c
> index bb45712..8076347 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -805,7 +805,6 @@ int page_referenced(struct page *page,
>  		    struct mem_cgroup *memcg,
>  		    unsigned long *vm_flags)
>  {
> -	int ret;
>  	int we_locked = 0;
>  	struct page_referenced_arg pra = {
>  		.mapcount = total_mapcount(page),
> @@ -839,7 +838,7 @@ int page_referenced(struct page *page,
>  		rwc.invalid_vma = invalid_page_referenced_vma;
>  	}
>  
> -	ret = rmap_walk(page, &rwc);
> +	rmap_walk(page, &rwc);
>  	*vm_flags = pra.vm_flags;
>  
>  	if (we_locked)
> 

Re: [RFC 03/11] mm: remove SWAP_DIRTY in ttu

[Anshuman Khandual]

On 03/02/2017 12:09 PM, Minchan Kim wrote:
> If we found lazyfree page is dirty, ttuo can just SetPageSwapBakced
> in there like PG_mlocked page and just return with SWAP_FAIL which
> is very natural because the page is not swappable right now so that
> vmscan can activate it. There is no point to introduce new return
> value SWAP_DIRTY in ttu at the moment.

Yeah makes sense. In the process, SetPageSwapBacked marking of the page
is moved from the shrink_page_list() to try_to_unmap_one().

Re: [RFC 04/11] mm: remove SWAP_MLOCK check for SWAP_SUCCESS in ttu

[Anshuman Khandual]

On 03/02/2017 12:09 PM, Minchan Kim wrote:
> If the page is mapped and rescue in ttuo, page_mapcount(page) == 0 cannot

Nit: "ttuo" is very cryptic. Please expand it.

> be true so page_mapcount check in ttu is enough to return SWAP_SUCCESS.
> IOW, SWAP_MLOCK check is redundant so remove it.

Right, page_mapcount(page) should be enough to tell whether swapping
out happened successfully or the page is still mapped in some page
table.

> 
> Signed-off-by: Minchan Kim <minchan@kernel.org>
> ---
>  mm/rmap.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/rmap.c b/mm/rmap.c
> index 3a14013..0a48958 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -1523,7 +1523,7 @@ int try_to_unmap(struct page *page, enum ttu_flags flags)
>  	else
>  		ret = rmap_walk(page, &rwc);
>  
> -	if (ret != SWAP_MLOCK && !page_mapcount(page))
> +	if (!page_mapcount(page))
>  		ret = SWAP_SUCCESS;
>  	return ret;
>  }
> 

Re: [RFC 00/11] make try_to_unmap simple

[Minchan Kim]

Hi Anshuman,

On Thu, Mar 02, 2017 at 07:52:27PM +0530, Anshuman Khandual wrote:
> On 03/02/2017 12:09 PM, Minchan Kim wrote:
> > Currently, try_to_unmap returns various return value(SWAP_SUCCESS,
> > SWAP_FAIL, SWAP_AGAIN, SWAP_DIRTY and SWAP_MLOCK). When I look into
> > that, it's unncessary complicated so this patch aims for cleaning
> > it up. Change ttu to boolean function so we can remove SWAP_AGAIN,
> > SWAP_DIRTY, SWAP_MLOCK.
> 
> It may be a trivial question but apart from being a cleanup does it
> help in improving it's callers some way ? Any other benefits ?

If you mean some performace, I don't think so. It just aims for cleanup
so caller don't need to think much about return value of try_to_unmap.
What he should consider is just "success/fail". Others will be done in
isolate/putback friends which makes API simple/easy to use.

Thanks.

> 
> --
> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> the body to majordomo@kvack.org.  For more info on Linux MM,
> see: http://www.linux-mm.org/ .
> Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>

Re: [RFC 03/11] mm: remove SWAP_DIRTY in ttu

[Minchan Kim]

Hi Hillf,

On Thu, Mar 02, 2017 at 03:34:45PM +0800, Hillf Danton wrote:
> 
> On March 02, 2017 2:39 PM Minchan Kim wrote: 
> > @@ -1424,7 +1424,8 @@ static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
> >  			} else if (!PageSwapBacked(page)) {
> >  				/* dirty MADV_FREE page */
> 
> Nit: enrich the comment please.

I guess what you wanted is not my patch doing but one merged already
so I just sent a small clean patch against of patch merged onto mmotm
to make thig logic clear. You are already Cced in there so you can
see it. Hope it well. If you want others, please tell me.
I will do something to make it clear.

Thanks for the review.

> >  				set_pte_at(mm, address, pvmw.pte, pteval);
> > -				ret = SWAP_DIRTY;
> > +				SetPageSwapBacked(page);
> > +				ret = SWAP_FAIL;
> >  				page_vma_mapped_walk_done(&pvmw);
> >  				break;
> >  			}
> 
> --
> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> the body to majordomo@kvack.org.  For more info on Linux MM,
> see: http://www.linux-mm.org/ .
> Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>

Re: [RFC 01/11] mm: use SWAP_SUCCESS instead of 0

[Minchan Kim]

On Thu, Mar 02, 2017 at 07:57:10PM +0530, Anshuman Khandual wrote:
> On 03/02/2017 12:09 PM, Minchan Kim wrote:
> > SWAP_SUCCESS defined value 0 can be changed always so don't rely on
> > it. Instead, use explict macro.
> 
> Right. But should not we move the changes to the callers last in the
> patch series after doing the cleanup to the try_to_unmap() function
> as intended first.

I don't understand what you are pointing out. Could you elaborate it
a bit?

Thanks.

> 
> > > Cc: Kirill A. Shutemov <kirill@shutemov.name>
> > Signed-off-by: Minchan Kim <minchan@kernel.org>
> > ---
> >  mm/huge_memory.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> > index 092cc5c..fe2ccd4 100644
> > --- a/mm/huge_memory.c
> > +++ b/mm/huge_memory.c
> > @@ -2114,7 +2114,7 @@ static void freeze_page(struct page *page)
> >  		ttu_flags |= TTU_MIGRATION;
> >  
> >  	ret = try_to_unmap(page, ttu_flags);
> > -	VM_BUG_ON_PAGE(ret, page);
> > +	VM_BUG_ON_PAGE(ret != SWAP_SUCCESS, page);
> >  }
> >  
> >  static void unfreeze_page(struct page *page)
> > 
> 
> --
> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> the body to majordomo@kvack.org.  For more info on Linux MM,
> see: http://www.linux-mm.org/ .
> Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>

Re: [RFC 02/11] mm: remove unncessary ret in page_referenced

[Minchan Kim]

On Thu, Mar 02, 2017 at 08:03:16PM +0530, Anshuman Khandual wrote:
> On 03/02/2017 12:09 PM, Minchan Kim wrote:
> > Anyone doesn't use ret variable. Remove it.
> > 
> 
> This change is correct. But not sure how this is related to
> try_to_unmap() clean up though.

In this patchset, I made rmap_walk void function with upcoming
patch so it's a preparation step for it.

> 
> 
> > Signed-off-by: Minchan Kim <minchan@kernel.org>
> > ---
> >  mm/rmap.c | 3 +--
> >  1 file changed, 1 insertion(+), 2 deletions(-)
> > 
> > diff --git a/mm/rmap.c b/mm/rmap.c
> > index bb45712..8076347 100644
> > --- a/mm/rmap.c
> > +++ b/mm/rmap.c
> > @@ -805,7 +805,6 @@ int page_referenced(struct page *page,
> >  		    struct mem_cgroup *memcg,
> >  		    unsigned long *vm_flags)
> >  {
> > -	int ret;
> >  	int we_locked = 0;
> >  	struct page_referenced_arg pra = {
> >  		.mapcount = total_mapcount(page),
> > @@ -839,7 +838,7 @@ int page_referenced(struct page *page,
> >  		rwc.invalid_vma = invalid_page_referenced_vma;
> >  	}
> >  
> > -	ret = rmap_walk(page, &rwc);
> > +	rmap_walk(page, &rwc);
> >  	*vm_flags = pra.vm_flags;
> >  
> >  	if (we_locked)
> > 
> 
> --
> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> the body to majordomo@kvack.org.  For more info on Linux MM,
> see: http://www.linux-mm.org/ .
> Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>

Re: [RFC 04/11] mm: remove SWAP_MLOCK check for SWAP_SUCCESS in ttu

[Minchan Kim]

On Thu, Mar 02, 2017 at 08:21:46PM +0530, Anshuman Khandual wrote:
> On 03/02/2017 12:09 PM, Minchan Kim wrote:
> > If the page is mapped and rescue in ttuo, page_mapcount(page) == 0 cannot
> 
> Nit: "ttuo" is very cryptic. Please expand it.

No problem.

> 
> > be true so page_mapcount check in ttu is enough to return SWAP_SUCCESS.
> > IOW, SWAP_MLOCK check is redundant so remove it.
> 
> Right, page_mapcount(page) should be enough to tell whether swapping
> out happened successfully or the page is still mapped in some page
> table.
> 

Thanks for the review, Anshuman!

Re: [RFC 00/11] make try_to_unmap simple

[Anshuman Khandual]

On 03/03/2017 07:41 AM, Minchan Kim wrote:
> Hi Anshuman,
> 
> On Thu, Mar 02, 2017 at 07:52:27PM +0530, Anshuman Khandual wrote:
>> On 03/02/2017 12:09 PM, Minchan Kim wrote:
>>> Currently, try_to_unmap returns various return value(SWAP_SUCCESS,
>>> SWAP_FAIL, SWAP_AGAIN, SWAP_DIRTY and SWAP_MLOCK). When I look into
>>> that, it's unncessary complicated so this patch aims for cleaning
>>> it up. Change ttu to boolean function so we can remove SWAP_AGAIN,
>>> SWAP_DIRTY, SWAP_MLOCK.
>>
>> It may be a trivial question but apart from being a cleanup does it
>> help in improving it's callers some way ? Any other benefits ?
> 
> If you mean some performace, I don't think so. It just aims for cleanup
> so caller don't need to think much about return value of try_to_unmap.
> What he should consider is just "success/fail". Others will be done in
> isolate/putback friends which makes API simple/easy to use.

Right, got it. Thanks !

Re: [RFC 05/11] mm: make the try_to_munlock void function

[Anshuman Khandual]

On 03/02/2017 12:09 PM, Minchan Kim wrote:
> try_to_munlock returns SWAP_MLOCK if the one of VMAs mapped
> the page has VM_LOCKED flag. In that time, VM set PG_mlocked to
> the page if the page is not pte-mapped THP which cannot be
> mlocked, either.

Right.

> 
> With that, __munlock_isolated_page can use PageMlocked to check
> whether try_to_munlock is successful or not without relying on
> try_to_munlock's retval. It helps to make ttu/ttuo simple with
> upcoming patches.

Right.

> 
> Cc: Vlastimil Babka <vbabka@suse.cz>
> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Signed-off-by: Minchan Kim <minchan@kernel.org>
> ---
>  include/linux/rmap.h |  2 +-
>  mm/mlock.c           |  6 ++----
>  mm/rmap.c            | 16 ++++------------
>  3 files changed, 7 insertions(+), 17 deletions(-)
> 
> diff --git a/include/linux/rmap.h b/include/linux/rmap.h
> index b556eef..1b0cd4c 100644
> --- a/include/linux/rmap.h
> +++ b/include/linux/rmap.h
> @@ -235,7 +235,7 @@ int page_mkclean(struct page *);
>   * called in munlock()/munmap() path to check for other vmas holding
>   * the page mlocked.
>   */
> -int try_to_munlock(struct page *);
> +void try_to_munlock(struct page *);
>  
>  void remove_migration_ptes(struct page *old, struct page *new, bool locked);
>  
> diff --git a/mm/mlock.c b/mm/mlock.c
> index cdbed8a..d34a540 100644
> --- a/mm/mlock.c
> +++ b/mm/mlock.c
> @@ -122,17 +122,15 @@ static bool __munlock_isolate_lru_page(struct page *page, bool getpage)
>   */
>  static void __munlock_isolated_page(struct page *page)
>  {
> -	int ret = SWAP_AGAIN;
> -
>  	/*
>  	 * Optimization: if the page was mapped just once, that's our mapping
>  	 * and we don't need to check all the other vmas.
>  	 */
>  	if (page_mapcount(page) > 1)
> -		ret = try_to_munlock(page);
> +		try_to_munlock(page);
>  
>  	/* Did try_to_unlock() succeed or punt? */
> -	if (ret != SWAP_MLOCK)
> +	if (!PageMlocked(page))

Checks if the page is still mlocked or not.

>  		count_vm_event(UNEVICTABLE_PGMUNLOCKED);
>  
>  	putback_lru_page(page);
> diff --git a/mm/rmap.c b/mm/rmap.c
> index 0a48958..61ae694 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -1540,18 +1540,10 @@ static int page_not_mapped(struct page *page)
>   * Called from munlock code.  Checks all of the VMAs mapping the page
>   * to make sure nobody else has this page mlocked. The page will be
>   * returned with PG_mlocked cleared if no other vmas have it mlocked.
> - *
> - * Return values are:
> - *
> - * SWAP_AGAIN	- no vma is holding page mlocked, or,
> - * SWAP_AGAIN	- page mapped in mlocked vma -- couldn't acquire mmap sem
> - * SWAP_FAIL	- page cannot be located at present
> - * SWAP_MLOCK	- page is now mlocked.
>   */
> -int try_to_munlock(struct page *page)
> -{
> -	int ret;
>  
> +void try_to_munlock(struct page *page)
> +{
>  	struct rmap_walk_control rwc = {
>  		.rmap_one = try_to_unmap_one,
>  		.arg = (void *)TTU_MUNLOCK,
> @@ -1561,9 +1553,9 @@ int try_to_munlock(struct page *page)
>  	};
>  
>  	VM_BUG_ON_PAGE(!PageLocked(page) || PageLRU(page), page);
> +	VM_BUG_ON_PAGE(PageMlocked(page), page);

We are calling on the page to see if its mlocked from any of it's
mapping VMAs. Then it is a possibility that the page is mlocked
and the above condition is true and we print VM BUG report there.
The point is if its a valid possibility why we have added the
above check ?

Re: [RFC 06/11] mm: remove SWAP_MLOCK in ttu

[Anshuman Khandual]

On 03/02/2017 12:09 PM, Minchan Kim wrote:
> ttu don't need to return SWAP_MLOCK. Instead, just return SWAP_FAIL
> because it means the page is not-swappable so it should move to
> another LRU list(active or unevictable). putback friends will
> move it to right list depending on the page's LRU flag.

Right, if it cannot be swapped out there is not much difference with
SWAP_FAIL once we change the callers who expected to see a SWAP_MLOCK
return instead.

> 
> A side effect is shrink_page_list accounts unevictable list movement
> by PGACTIVATE but I don't think it corrupts something severe.

Not sure I got that, could you please elaborate on this. We will still
activate the page and put it in an appropriate LRU list if it is marked
mlocked ?

Re: [RFC 07/11] mm: remove SWAP_AGAIN in ttu

[Anshuman Khandual]

On 03/02/2017 12:09 PM, Minchan Kim wrote:
> In 2002, [1] introduced SWAP_AGAIN.
> At that time, ttuo used spin_trylock(&mm->page_table_lock) so it's

Small nit: Please expand "ttuo" here. TTU in the first place is also
not very clear but we have that in many places.

> really easy to contend and fail to hold a lock so SWAP_AGAIN to keep
> LRU status makes sense.

Okay.

> 
> However, now we changed it to mutex-based lock and be able to block
> without skip pte so there is a few of small window to return
> SWAP_AGAIN so remove SWAP_AGAIN and just return SWAP_FAIL.

Makes sense.

> 
> [1] c48c43e, minimal rmap
> Signed-off-by: Minchan Kim <minchan@kernel.org>
> ---
>  mm/rmap.c   | 11 +++--------
>  mm/vmscan.c |  2 --
>  2 files changed, 3 insertions(+), 10 deletions(-)
> 
> diff --git a/mm/rmap.c b/mm/rmap.c
> index 47898a1..da18f21 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -1492,13 +1492,10 @@ static int page_mapcount_is_zero(struct page *page)
>   * Return values are:
>   *
>   * SWAP_SUCCESS	- we succeeded in removing all mappings
> - * SWAP_AGAIN	- we missed a mapping, try again later
>   * SWAP_FAIL	- the page is unswappable
>   */
>  int try_to_unmap(struct page *page, enum ttu_flags flags)
>  {
> -	int ret;
> -
>  	struct rmap_walk_control rwc = {
>  		.rmap_one = try_to_unmap_one,
>  		.arg = (void *)flags,
> @@ -1518,13 +1515,11 @@ int try_to_unmap(struct page *page, enum ttu_flags flags)
>  		rwc.invalid_vma = invalid_migration_vma;
>  
>  	if (flags & TTU_RMAP_LOCKED)
> -		ret = rmap_walk_locked(page, &rwc);
> +		rmap_walk_locked(page, &rwc);
>  	else
> -		ret = rmap_walk(page, &rwc);
> +		rmap_walk(page, &rwc);
>  
> -	if (!page_mapcount(page))
> -		ret = SWAP_SUCCESS;
> -	return ret;
> +	return !page_mapcount(page) ? SWAP_SUCCESS: SWAP_FAIL;

Its very simple now. So after the rmap_walk() if page is not mapped any
more return SWAP_SUCCESS otherwise SWAP_FAIL.

Re: [RFC 11/11] mm: remove SWAP_[SUCCESS|AGAIN|FAIL]

[Anshuman Khandual]

On 03/02/2017 12:09 PM, Minchan Kim wrote:
> There is no user for it. Remove it.

Last patches in the series prepared ground for this removal. The
entire series looks pretty straight forward. As it does not change
any functionality, wondering what kind of tests this should go
through to look for any potential problems.

Re: [RFC 05/11] mm: make the try_to_munlock void function

[Minchan Kim]

On Fri, Mar 03, 2017 at 05:13:54PM +0530, Anshuman Khandual wrote:
> On 03/02/2017 12:09 PM, Minchan Kim wrote:
> > try_to_munlock returns SWAP_MLOCK if the one of VMAs mapped
> > the page has VM_LOCKED flag. In that time, VM set PG_mlocked to
> > the page if the page is not pte-mapped THP which cannot be
> > mlocked, either.
> 
> Right.
> 
> > 
> > With that, __munlock_isolated_page can use PageMlocked to check
> > whether try_to_munlock is successful or not without relying on
> > try_to_munlock's retval. It helps to make ttu/ttuo simple with
> > upcoming patches.
> 
> Right.
> 
> > 
> > Cc: Vlastimil Babka <vbabka@suse.cz>
> > Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> > Signed-off-by: Minchan Kim <minchan@kernel.org>
> > ---
> >  include/linux/rmap.h |  2 +-
> >  mm/mlock.c           |  6 ++----
> >  mm/rmap.c            | 16 ++++------------
> >  3 files changed, 7 insertions(+), 17 deletions(-)
> > 
> > diff --git a/include/linux/rmap.h b/include/linux/rmap.h
> > index b556eef..1b0cd4c 100644
> > --- a/include/linux/rmap.h
> > +++ b/include/linux/rmap.h
> > @@ -235,7 +235,7 @@ int page_mkclean(struct page *);
> >   * called in munlock()/munmap() path to check for other vmas holding
> >   * the page mlocked.
> >   */
> > -int try_to_munlock(struct page *);
> > +void try_to_munlock(struct page *);
> >  
> >  void remove_migration_ptes(struct page *old, struct page *new, bool locked);
> >  
> > diff --git a/mm/mlock.c b/mm/mlock.c
> > index cdbed8a..d34a540 100644
> > --- a/mm/mlock.c
> > +++ b/mm/mlock.c
> > @@ -122,17 +122,15 @@ static bool __munlock_isolate_lru_page(struct page *page, bool getpage)
> >   */
> >  static void __munlock_isolated_page(struct page *page)
> >  {
> > -	int ret = SWAP_AGAIN;
> > -
> >  	/*
> >  	 * Optimization: if the page was mapped just once, that's our mapping
> >  	 * and we don't need to check all the other vmas.
> >  	 */
> >  	if (page_mapcount(page) > 1)
> > -		ret = try_to_munlock(page);
> > +		try_to_munlock(page);
> >  
> >  	/* Did try_to_unlock() succeed or punt? */
> > -	if (ret != SWAP_MLOCK)
> > +	if (!PageMlocked(page))
> 
> Checks if the page is still mlocked or not.
> 
> >  		count_vm_event(UNEVICTABLE_PGMUNLOCKED);
> >  
> >  	putback_lru_page(page);
> > diff --git a/mm/rmap.c b/mm/rmap.c
> > index 0a48958..61ae694 100644
> > --- a/mm/rmap.c
> > +++ b/mm/rmap.c
> > @@ -1540,18 +1540,10 @@ static int page_not_mapped(struct page *page)
> >   * Called from munlock code.  Checks all of the VMAs mapping the page
> >   * to make sure nobody else has this page mlocked. The page will be
> >   * returned with PG_mlocked cleared if no other vmas have it mlocked.
> > - *
> > - * Return values are:
> > - *
> > - * SWAP_AGAIN	- no vma is holding page mlocked, or,
> > - * SWAP_AGAIN	- page mapped in mlocked vma -- couldn't acquire mmap sem
> > - * SWAP_FAIL	- page cannot be located at present
> > - * SWAP_MLOCK	- page is now mlocked.
> >   */
> > -int try_to_munlock(struct page *page)
> > -{
> > -	int ret;
> >  
> > +void try_to_munlock(struct page *page)
> > +{
> >  	struct rmap_walk_control rwc = {
> >  		.rmap_one = try_to_unmap_one,
> >  		.arg = (void *)TTU_MUNLOCK,
> > @@ -1561,9 +1553,9 @@ int try_to_munlock(struct page *page)
> >  	};
> >  
> >  	VM_BUG_ON_PAGE(!PageLocked(page) || PageLRU(page), page);
> > +	VM_BUG_ON_PAGE(PageMlocked(page), page);
> 
> We are calling on the page to see if its mlocked from any of it's
> mapping VMAs. Then it is a possibility that the page is mlocked
> and the above condition is true and we print VM BUG report there.
> The point is if its a valid possibility why we have added the
> above check ?

If I read code properly,  __munlock_isolated_page calls try_to_munlock
always pass the TestClearPageMlocked page to try_to_munlock.
(e.g., munlock_vma_page and __munlock_pagevec) so I thought
try_to_munlock should be called non-PG_mlocked page and try_to_unmap_one
returns PG_mlocked page once it found a VM_LOCKED VMA for a page.
IOW, non-PG_mlocked page is precondition for try_to_munlock.

Re: [RFC 06/11] mm: remove SWAP_MLOCK in ttu

[Minchan Kim]

Hi Anshuman,

On Fri, Mar 03, 2017 at 06:06:38PM +0530, Anshuman Khandual wrote:
> On 03/02/2017 12:09 PM, Minchan Kim wrote:
> > ttu don't need to return SWAP_MLOCK. Instead, just return SWAP_FAIL
> > because it means the page is not-swappable so it should move to
> > another LRU list(active or unevictable). putback friends will
> > move it to right list depending on the page's LRU flag.
> 
> Right, if it cannot be swapped out there is not much difference with
> SWAP_FAIL once we change the callers who expected to see a SWAP_MLOCK
> return instead.
> 
> > 
> > A side effect is shrink_page_list accounts unevictable list movement
> > by PGACTIVATE but I don't think it corrupts something severe.
> 
> Not sure I got that, could you please elaborate on this. We will still
> activate the page and put it in an appropriate LRU list if it is marked
> mlocked ?

Right. putback_iactive_pages/putback_lru_page has a logic to filter
out unevictable pages and move them to unevictable LRU list so it
doesn't break LRU change behavior but the concern is until now,
we have accounted PGACTIVATE for only evictable LRU list page but
by this change, it accounts it to unevictable LRU list as well.
However, although I don't think it's big problem in real practice,
we can fix it simply with checking PG_mlocked if someone reports.

Thanks.


> 
> --
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Re: [RFC 07/11] mm: remove SWAP_AGAIN in ttu

[Minchan Kim]

On Fri, Mar 03, 2017 at 06:24:06PM +0530, Anshuman Khandual wrote:
> On 03/02/2017 12:09 PM, Minchan Kim wrote:
> > In 2002, [1] introduced SWAP_AGAIN.
> > At that time, ttuo used spin_trylock(&mm->page_table_lock) so it's
> 
> Small nit: Please expand "ttuo" here. TTU in the first place is also
> not very clear but we have that in many places.

No problem.

Re: [RFC 11/11] mm: remove SWAP_[SUCCESS|AGAIN|FAIL]

[Minchan Kim]

On Fri, Mar 03, 2017 at 06:34:15PM +0530, Anshuman Khandual wrote:
> On 03/02/2017 12:09 PM, Minchan Kim wrote:
> > There is no user for it. Remove it.
> 
> Last patches in the series prepared ground for this removal. The
> entire series looks pretty straight forward. As it does not change

Thanks.

> any functionality, wondering what kind of tests this should go
> through to look for any potential problems.

I don't think it can change something severe, either but one thing
I want to check is handling of mlocked pages part so I will do
some test for that.

Thanks for the review, Anshuman!

Re: [RFC 01/11] mm: use SWAP_SUCCESS instead of 0

[Anshuman Khandual]

On 03/03/2017 08:31 AM, Minchan Kim wrote:
> On Thu, Mar 02, 2017 at 07:57:10PM +0530, Anshuman Khandual wrote:
>> On 03/02/2017 12:09 PM, Minchan Kim wrote:
>>> SWAP_SUCCESS defined value 0 can be changed always so don't rely on
>>> it. Instead, use explict macro.
>>
>> Right. But should not we move the changes to the callers last in the
>> patch series after doing the cleanup to the try_to_unmap() function
>> as intended first.
> 
> I don't understand what you are pointing out. Could you elaborate it
> a bit?

I was just referring to the order of this patch in the series and
thinking if it would have been better if this patch would be at a
later stage in the series. But I guess its okay as we are any way
dropping off SWAP_FAIL, SWAP_SUCCESS etc in the end.

Re: [RFC 05/11] mm: make the try_to_munlock void function

[Anshuman Khandual]

On 03/06/2017 07:39 AM, Minchan Kim wrote:
> On Fri, Mar 03, 2017 at 05:13:54PM +0530, Anshuman Khandual wrote:
>> On 03/02/2017 12:09 PM, Minchan Kim wrote:
>>> try_to_munlock returns SWAP_MLOCK if the one of VMAs mapped
>>> the page has VM_LOCKED flag. In that time, VM set PG_mlocked to
>>> the page if the page is not pte-mapped THP which cannot be
>>> mlocked, either.
>>
>> Right.
>>
>>>
>>> With that, __munlock_isolated_page can use PageMlocked to check
>>> whether try_to_munlock is successful or not without relying on
>>> try_to_munlock's retval. It helps to make ttu/ttuo simple with
>>> upcoming patches.
>>
>> Right.
>>
>>>
>>> Cc: Vlastimil Babka <vbabka@suse.cz>
>>> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
>>> Signed-off-by: Minchan Kim <minchan@kernel.org>
>>> ---
>>>  include/linux/rmap.h |  2 +-
>>>  mm/mlock.c           |  6 ++----
>>>  mm/rmap.c            | 16 ++++------------
>>>  3 files changed, 7 insertions(+), 17 deletions(-)
>>>
>>> diff --git a/include/linux/rmap.h b/include/linux/rmap.h
>>> index b556eef..1b0cd4c 100644
>>> --- a/include/linux/rmap.h
>>> +++ b/include/linux/rmap.h
>>> @@ -235,7 +235,7 @@ int page_mkclean(struct page *);
>>>   * called in munlock()/munmap() path to check for other vmas holding
>>>   * the page mlocked.
>>>   */
>>> -int try_to_munlock(struct page *);
>>> +void try_to_munlock(struct page *);
>>>  
>>>  void remove_migration_ptes(struct page *old, struct page *new, bool locked);
>>>  
>>> diff --git a/mm/mlock.c b/mm/mlock.c
>>> index cdbed8a..d34a540 100644
>>> --- a/mm/mlock.c
>>> +++ b/mm/mlock.c
>>> @@ -122,17 +122,15 @@ static bool __munlock_isolate_lru_page(struct page *page, bool getpage)
>>>   */
>>>  static void __munlock_isolated_page(struct page *page)
>>>  {
>>> -	int ret = SWAP_AGAIN;
>>> -
>>>  	/*
>>>  	 * Optimization: if the page was mapped just once, that's our mapping
>>>  	 * and we don't need to check all the other vmas.
>>>  	 */
>>>  	if (page_mapcount(page) > 1)
>>> -		ret = try_to_munlock(page);
>>> +		try_to_munlock(page);
>>>  
>>>  	/* Did try_to_unlock() succeed or punt? */
>>> -	if (ret != SWAP_MLOCK)
>>> +	if (!PageMlocked(page))
>>
>> Checks if the page is still mlocked or not.
>>
>>>  		count_vm_event(UNEVICTABLE_PGMUNLOCKED);
>>>  
>>>  	putback_lru_page(page);
>>> diff --git a/mm/rmap.c b/mm/rmap.c
>>> index 0a48958..61ae694 100644
>>> --- a/mm/rmap.c
>>> +++ b/mm/rmap.c
>>> @@ -1540,18 +1540,10 @@ static int page_not_mapped(struct page *page)
>>>   * Called from munlock code.  Checks all of the VMAs mapping the page
>>>   * to make sure nobody else has this page mlocked. The page will be
>>>   * returned with PG_mlocked cleared if no other vmas have it mlocked.
>>> - *
>>> - * Return values are:
>>> - *
>>> - * SWAP_AGAIN	- no vma is holding page mlocked, or,
>>> - * SWAP_AGAIN	- page mapped in mlocked vma -- couldn't acquire mmap sem
>>> - * SWAP_FAIL	- page cannot be located at present
>>> - * SWAP_MLOCK	- page is now mlocked.
>>>   */
>>> -int try_to_munlock(struct page *page)
>>> -{
>>> -	int ret;
>>>  
>>> +void try_to_munlock(struct page *page)
>>> +{
>>>  	struct rmap_walk_control rwc = {
>>>  		.rmap_one = try_to_unmap_one,
>>>  		.arg = (void *)TTU_MUNLOCK,
>>> @@ -1561,9 +1553,9 @@ int try_to_munlock(struct page *page)
>>>  	};
>>>  
>>>  	VM_BUG_ON_PAGE(!PageLocked(page) || PageLRU(page), page);
>>> +	VM_BUG_ON_PAGE(PageMlocked(page), page);
>>
>> We are calling on the page to see if its mlocked from any of it's
>> mapping VMAs. Then it is a possibility that the page is mlocked
>> and the above condition is true and we print VM BUG report there.
>> The point is if its a valid possibility why we have added the
>> above check ?
> 
> If I read code properly,  __munlock_isolated_page calls try_to_munlock
> always pass the TestClearPageMlocked page to try_to_munlock.

Right.

> (e.g., munlock_vma_page and __munlock_pagevec) so I thought
> try_to_munlock should be called non-PG_mlocked page and try_to_unmap_one
> returns PG_mlocked page once it found a VM_LOCKED VMA for a page.
> IOW, non-PG_mlocked page is precondition for try_to_munlock.

Okay, I have missed that part. Nonetheless this is a separate issue,
should be part of a different patch ? Not inside these cleanups.

Re: [RFC 05/11] mm: make the try_to_munlock void function

[Minchan Kim]

Hi Anshuman,

On Mon, Mar 06, 2017 at 03:10:17PM +0530, Anshuman Khandual wrote:
> On 03/06/2017 07:39 AM, Minchan Kim wrote:
> > On Fri, Mar 03, 2017 at 05:13:54PM +0530, Anshuman Khandual wrote:
> >> On 03/02/2017 12:09 PM, Minchan Kim wrote:
> >>> try_to_munlock returns SWAP_MLOCK if the one of VMAs mapped
> >>> the page has VM_LOCKED flag. In that time, VM set PG_mlocked to
> >>> the page if the page is not pte-mapped THP which cannot be
> >>> mlocked, either.
> >>
> >> Right.
> >>
> >>>
> >>> With that, __munlock_isolated_page can use PageMlocked to check
> >>> whether try_to_munlock is successful or not without relying on
> >>> try_to_munlock's retval. It helps to make ttu/ttuo simple with
> >>> upcoming patches.
> >>
> >> Right.
> >>
> >>>
> >>> Cc: Vlastimil Babka <vbabka@suse.cz>
> >>> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> >>> Signed-off-by: Minchan Kim <minchan@kernel.org>
> >>> ---
> >>>  include/linux/rmap.h |  2 +-
> >>>  mm/mlock.c           |  6 ++----
> >>>  mm/rmap.c            | 16 ++++------------
> >>>  3 files changed, 7 insertions(+), 17 deletions(-)
> >>>
> >>> diff --git a/include/linux/rmap.h b/include/linux/rmap.h
> >>> index b556eef..1b0cd4c 100644
> >>> --- a/include/linux/rmap.h
> >>> +++ b/include/linux/rmap.h
> >>> @@ -235,7 +235,7 @@ int page_mkclean(struct page *);
> >>>   * called in munlock()/munmap() path to check for other vmas holding
> >>>   * the page mlocked.
> >>>   */
> >>> -int try_to_munlock(struct page *);
> >>> +void try_to_munlock(struct page *);
> >>>  
> >>>  void remove_migration_ptes(struct page *old, struct page *new, bool locked);
> >>>  
> >>> diff --git a/mm/mlock.c b/mm/mlock.c
> >>> index cdbed8a..d34a540 100644
> >>> --- a/mm/mlock.c
> >>> +++ b/mm/mlock.c
> >>> @@ -122,17 +122,15 @@ static bool __munlock_isolate_lru_page(struct page *page, bool getpage)
> >>>   */
> >>>  static void __munlock_isolated_page(struct page *page)
> >>>  {
> >>> -	int ret = SWAP_AGAIN;
> >>> -
> >>>  	/*
> >>>  	 * Optimization: if the page was mapped just once, that's our mapping
> >>>  	 * and we don't need to check all the other vmas.
> >>>  	 */
> >>>  	if (page_mapcount(page) > 1)
> >>> -		ret = try_to_munlock(page);
> >>> +		try_to_munlock(page);
> >>>  
> >>>  	/* Did try_to_unlock() succeed or punt? */
> >>> -	if (ret != SWAP_MLOCK)
> >>> +	if (!PageMlocked(page))
> >>
> >> Checks if the page is still mlocked or not.
> >>
> >>>  		count_vm_event(UNEVICTABLE_PGMUNLOCKED);
> >>>  
> >>>  	putback_lru_page(page);
> >>> diff --git a/mm/rmap.c b/mm/rmap.c
> >>> index 0a48958..61ae694 100644
> >>> --- a/mm/rmap.c
> >>> +++ b/mm/rmap.c
> >>> @@ -1540,18 +1540,10 @@ static int page_not_mapped(struct page *page)
> >>>   * Called from munlock code.  Checks all of the VMAs mapping the page
> >>>   * to make sure nobody else has this page mlocked. The page will be
> >>>   * returned with PG_mlocked cleared if no other vmas have it mlocked.
> >>> - *
> >>> - * Return values are:
> >>> - *
> >>> - * SWAP_AGAIN	- no vma is holding page mlocked, or,
> >>> - * SWAP_AGAIN	- page mapped in mlocked vma -- couldn't acquire mmap sem
> >>> - * SWAP_FAIL	- page cannot be located at present
> >>> - * SWAP_MLOCK	- page is now mlocked.
> >>>   */
> >>> -int try_to_munlock(struct page *page)
> >>> -{
> >>> -	int ret;
> >>>  
> >>> +void try_to_munlock(struct page *page)
> >>> +{
> >>>  	struct rmap_walk_control rwc = {
> >>>  		.rmap_one = try_to_unmap_one,
> >>>  		.arg = (void *)TTU_MUNLOCK,
> >>> @@ -1561,9 +1553,9 @@ int try_to_munlock(struct page *page)
> >>>  	};
> >>>  
> >>>  	VM_BUG_ON_PAGE(!PageLocked(page) || PageLRU(page), page);
> >>> +	VM_BUG_ON_PAGE(PageMlocked(page), page);
> >>
> >> We are calling on the page to see if its mlocked from any of it's
> >> mapping VMAs. Then it is a possibility that the page is mlocked
> >> and the above condition is true and we print VM BUG report there.
> >> The point is if its a valid possibility why we have added the
> >> above check ?
> > 
> > If I read code properly,  __munlock_isolated_page calls try_to_munlock
> > always pass the TestClearPageMlocked page to try_to_munlock.
> 
> Right.
> 
> > (e.g., munlock_vma_page and __munlock_pagevec) so I thought
> > try_to_munlock should be called non-PG_mlocked page and try_to_unmap_one
> > returns PG_mlocked page once it found a VM_LOCKED VMA for a page.
> > IOW, non-PG_mlocked page is precondition for try_to_munlock.
> 
> Okay, I have missed that part. Nonetheless this is a separate issue,
> should be part of a different patch ? Not inside these cleanups.

If that precondition is not true, this patch changes the behavior
slightly.

        UNEVICTABLE_PGMUNLOCKED count mistmatch compared to old.

I wanted to catch it up. If you still think it's separate issue,
I will do. Please tell me. However, I still think it's no problem
to merge it in this clean up patch.

Thanks.

Re: [RFC 05/11] mm: make the try_to_munlock void function

[Anshuman Khandual]

On 03/07/2017 12:20 PM, Minchan Kim wrote:
> Hi Anshuman,
> 
> On Mon, Mar 06, 2017 at 03:10:17PM +0530, Anshuman Khandual wrote:
>> On 03/06/2017 07:39 AM, Minchan Kim wrote:
>>> On Fri, Mar 03, 2017 at 05:13:54PM +0530, Anshuman Khandual wrote:
>>>> On 03/02/2017 12:09 PM, Minchan Kim wrote:
>>>>> try_to_munlock returns SWAP_MLOCK if the one of VMAs mapped
>>>>> the page has VM_LOCKED flag. In that time, VM set PG_mlocked to
>>>>> the page if the page is not pte-mapped THP which cannot be
>>>>> mlocked, either.
>>>> Right.
>>>>
>>>>> With that, __munlock_isolated_page can use PageMlocked to check
>>>>> whether try_to_munlock is successful or not without relying on
>>>>> try_to_munlock's retval. It helps to make ttu/ttuo simple with
>>>>> upcoming patches.
>>>> Right.
>>>>
>>>>> Cc: Vlastimil Babka <vbabka@suse.cz>
>>>>> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
>>>>> Signed-off-by: Minchan Kim <minchan@kernel.org>
>>>>> ---
>>>>>  include/linux/rmap.h |  2 +-
>>>>>  mm/mlock.c           |  6 ++----
>>>>>  mm/rmap.c            | 16 ++++------------
>>>>>  3 files changed, 7 insertions(+), 17 deletions(-)
>>>>>
>>>>> diff --git a/include/linux/rmap.h b/include/linux/rmap.h
>>>>> index b556eef..1b0cd4c 100644
>>>>> --- a/include/linux/rmap.h
>>>>> +++ b/include/linux/rmap.h
>>>>> @@ -235,7 +235,7 @@ int page_mkclean(struct page *);
>>>>>   * called in munlock()/munmap() path to check for other vmas holding
>>>>>   * the page mlocked.
>>>>>   */
>>>>> -int try_to_munlock(struct page *);
>>>>> +void try_to_munlock(struct page *);
>>>>>  
>>>>>  void remove_migration_ptes(struct page *old, struct page *new, bool locked);
>>>>>  
>>>>> diff --git a/mm/mlock.c b/mm/mlock.c
>>>>> index cdbed8a..d34a540 100644
>>>>> --- a/mm/mlock.c
>>>>> +++ b/mm/mlock.c
>>>>> @@ -122,17 +122,15 @@ static bool __munlock_isolate_lru_page(struct page *page, bool getpage)
>>>>>   */
>>>>>  static void __munlock_isolated_page(struct page *page)
>>>>>  {
>>>>> -	int ret = SWAP_AGAIN;
>>>>> -
>>>>>  	/*
>>>>>  	 * Optimization: if the page was mapped just once, that's our mapping
>>>>>  	 * and we don't need to check all the other vmas.
>>>>>  	 */
>>>>>  	if (page_mapcount(page) > 1)
>>>>> -		ret = try_to_munlock(page);
>>>>> +		try_to_munlock(page);
>>>>>  
>>>>>  	/* Did try_to_unlock() succeed or punt? */
>>>>> -	if (ret != SWAP_MLOCK)
>>>>> +	if (!PageMlocked(page))
>>>> Checks if the page is still mlocked or not.
>>>>
>>>>>  		count_vm_event(UNEVICTABLE_PGMUNLOCKED);
>>>>>  
>>>>>  	putback_lru_page(page);
>>>>> diff --git a/mm/rmap.c b/mm/rmap.c
>>>>> index 0a48958..61ae694 100644
>>>>> --- a/mm/rmap.c
>>>>> +++ b/mm/rmap.c
>>>>> @@ -1540,18 +1540,10 @@ static int page_not_mapped(struct page *page)
>>>>>   * Called from munlock code.  Checks all of the VMAs mapping the page
>>>>>   * to make sure nobody else has this page mlocked. The page will be
>>>>>   * returned with PG_mlocked cleared if no other vmas have it mlocked.
>>>>> - *
>>>>> - * Return values are:
>>>>> - *
>>>>> - * SWAP_AGAIN	- no vma is holding page mlocked, or,
>>>>> - * SWAP_AGAIN	- page mapped in mlocked vma -- couldn't acquire mmap sem
>>>>> - * SWAP_FAIL	- page cannot be located at present
>>>>> - * SWAP_MLOCK	- page is now mlocked.
>>>>>   */
>>>>> -int try_to_munlock(struct page *page)
>>>>> -{
>>>>> -	int ret;
>>>>>  
>>>>> +void try_to_munlock(struct page *page)
>>>>> +{
>>>>>  	struct rmap_walk_control rwc = {
>>>>>  		.rmap_one = try_to_unmap_one,
>>>>>  		.arg = (void *)TTU_MUNLOCK,
>>>>> @@ -1561,9 +1553,9 @@ int try_to_munlock(struct page *page)
>>>>>  	};
>>>>>  
>>>>>  	VM_BUG_ON_PAGE(!PageLocked(page) || PageLRU(page), page);
>>>>> +	VM_BUG_ON_PAGE(PageMlocked(page), page);
>>>> We are calling on the page to see if its mlocked from any of it's
>>>> mapping VMAs. Then it is a possibility that the page is mlocked
>>>> and the above condition is true and we print VM BUG report there.
>>>> The point is if its a valid possibility why we have added the
>>>> above check ?
>>> If I read code properly,  __munlock_isolated_page calls try_to_munlock
>>> always pass the TestClearPageMlocked page to try_to_munlock.
>> Right.
>>
>>> (e.g., munlock_vma_page and __munlock_pagevec) so I thought
>>> try_to_munlock should be called non-PG_mlocked page and try_to_unmap_one
>>> returns PG_mlocked page once it found a VM_LOCKED VMA for a page.
>>> IOW, non-PG_mlocked page is precondition for try_to_munlock.
>> Okay, I have missed that part. Nonetheless this is a separate issue,
>> should be part of a different patch ? Not inside these cleanups.
> If that precondition is not true, this patch changes the behavior
> slightly.
> 
>         UNEVICTABLE_PGMUNLOCKED count mistmatch compared to old.
> 
> I wanted to catch it up. If you still think it's separate issue,
> I will do. Please tell me. However, I still think it's no problem
> to merge it in this clean up patch.

Got it, its okay. Let this change be part of this patch itself.

Re: [RFC 01/11] mm: use SWAP_SUCCESS instead of 0

[Kirill A. Shutemov]

On Thu, Mar 02, 2017 at 03:39:15PM +0900, Minchan Kim wrote:
> SWAP_SUCCESS defined value 0 can be changed always so don't rely on
> it. Instead, use explict macro.

I'm okay with this as long as it's prepartion for something meaningful.
0 as success is widely used. I don't think replacing it's with macro here
has value on its own.

-- 
 Kirill A. Shutemov

Re: [RFC 02/11] mm: remove unncessary ret in page_referenced

[Kirill A. Shutemov]

On Thu, Mar 02, 2017 at 03:39:16PM +0900, Minchan Kim wrote:
> Anyone doesn't use ret variable. Remove it.
> 
> Signed-off-by: Minchan Kim <minchan@kernel.org>

Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>

-- 
 Kirill A. Shutemov

Re: [RFC 03/11] mm: remove SWAP_DIRTY in ttu

[Kirill A. Shutemov]

On Thu, Mar 02, 2017 at 03:39:17PM +0900, Minchan Kim wrote:
> If we found lazyfree page is dirty, ttuo can just SetPageSwapBakced
> in there like PG_mlocked page and just return with SWAP_FAIL which
> is very natural because the page is not swappable right now so that
> vmscan can activate it. There is no point to introduce new return
> value SWAP_DIRTY in ttu at the moment.
> 
> Cc: Shaohua Li <shli@kernel.org>
> Signed-off-by: Minchan Kim <minchan@kernel.org>

Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>

-- 
 Kirill A. Shutemov

Re: [RFC 04/11] mm: remove SWAP_MLOCK check for SWAP_SUCCESS in ttu

[Kirill A. Shutemov]

On Thu, Mar 02, 2017 at 03:39:18PM +0900, Minchan Kim wrote:
> If the page is mapped and rescue in ttuo, page_mapcount(page) == 0 cannot
> be true so page_mapcount check in ttu is enough to return SWAP_SUCCESS.
> IOW, SWAP_MLOCK check is redundant so remove it.
> 
> Signed-off-by: Minchan Kim <minchan@kernel.org>
> ---
>  mm/rmap.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/rmap.c b/mm/rmap.c
> index 3a14013..0a48958 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -1523,7 +1523,7 @@ int try_to_unmap(struct page *page, enum ttu_flags flags)
>  	else
>  		ret = rmap_walk(page, &rwc);
>  
> -	if (ret != SWAP_MLOCK && !page_mapcount(page))
> +	if (!page_mapcount(page))

Hm. I think there's bug in current code.
It should be !total_mapcount(page) otherwise it can be false-positive if
there's THP mapped with PTEs.

And in this case ret != SWAP_MLOCK is helpful to cut down some cost.
Althouth it should be fine to remove it, I guess.

-- 
 Kirill A. Shutemov

Re: [RFC 05/11] mm: make the try_to_munlock void function

[Kirill A. Shutemov]

On Thu, Mar 02, 2017 at 03:39:19PM +0900, Minchan Kim wrote:
> try_to_munlock returns SWAP_MLOCK if the one of VMAs mapped
> the page has VM_LOCKED flag. In that time, VM set PG_mlocked to
> the page if the page is not pte-mapped THP which cannot be
> mlocked, either.
> 
> With that, __munlock_isolated_page can use PageMlocked to check
> whether try_to_munlock is successful or not without relying on
> try_to_munlock's retval. It helps to make ttu/ttuo simple with
> upcoming patches.

I *think* you're correct, but it took time to wrap my head around.
We basically rely on try_to_munlock() never caller for PTE-mapped THP.
And we don't at the moment.

It worth adding something like

	VM_BUG_ON_PAGE(PageCompound(page) && PageDoubleMap(page), page);

into try_to_munlock().

Otherwise looks good to me.

Will free adding my Acked-by once this nit is addressed.

-- 
 Kirill A. Shutemov

Re: [RFC 06/11] mm: remove SWAP_MLOCK in ttu

[Kirill A. Shutemov]

On Mon, Mar 06, 2017 at 11:15:08AM +0900, Minchan Kim wrote:
> Hi Anshuman,
> 
> On Fri, Mar 03, 2017 at 06:06:38PM +0530, Anshuman Khandual wrote:
> > On 03/02/2017 12:09 PM, Minchan Kim wrote:
> > > ttu don't need to return SWAP_MLOCK. Instead, just return SWAP_FAIL
> > > because it means the page is not-swappable so it should move to
> > > another LRU list(active or unevictable). putback friends will
> > > move it to right list depending on the page's LRU flag.
> > 
> > Right, if it cannot be swapped out there is not much difference with
> > SWAP_FAIL once we change the callers who expected to see a SWAP_MLOCK
> > return instead.
> > 
> > > 
> > > A side effect is shrink_page_list accounts unevictable list movement
> > > by PGACTIVATE but I don't think it corrupts something severe.
> > 
> > Not sure I got that, could you please elaborate on this. We will still
> > activate the page and put it in an appropriate LRU list if it is marked
> > mlocked ?
> 
> Right. putback_iactive_pages/putback_lru_page has a logic to filter
> out unevictable pages and move them to unevictable LRU list so it
> doesn't break LRU change behavior but the concern is until now,
> we have accounted PGACTIVATE for only evictable LRU list page but
> by this change, it accounts it to unevictable LRU list as well.
> However, although I don't think it's big problem in real practice,
> we can fix it simply with checking PG_mlocked if someone reports.

I think it's better to do this pro-actively. Let's hide both pgactivate++
and SetPageActive() under "if (!PageMlocked())".
SetPageActive() is not free.

-- 
 Kirill A. Shutemov

Re: [RFC 01/11] mm: use SWAP_SUCCESS instead of 0

[Minchan Kim]

Hi Kirill,

On Tue, Mar 07, 2017 at 05:19:33PM +0300, Kirill A. Shutemov wrote:
> On Thu, Mar 02, 2017 at 03:39:15PM +0900, Minchan Kim wrote:
> > SWAP_SUCCESS defined value 0 can be changed always so don't rely on
> > it. Instead, use explict macro.
> 
> I'm okay with this as long as it's prepartion for something meaningful.
> 0 as success is widely used. I don't think replacing it's with macro here
> has value on its own.

It's the prepartion for making try_to_unmap return bool type but strictly
speaking, it's not necessary but I wanted to replace it with SWAP_SUCCESS
in this chance because it has several *defined* return type so it would
make it clear if we use one of those defiend type, IMO.
However, my thumb rule is to keep author/maintainer's credit for trivial
case and it seems you don't like so I will drop in next spin.

Thanks.


> 
> -- 
>  Kirill A. Shutemov
> 
> --
> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> the body to majordomo@kvack.org.  For more info on Linux MM,
> see: http://www.linux-mm.org/ .
> Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>

Re: [RFC 04/11] mm: remove SWAP_MLOCK check for SWAP_SUCCESS in ttu

[Minchan Kim]

On Tue, Mar 07, 2017 at 05:26:43PM +0300, Kirill A. Shutemov wrote:
> On Thu, Mar 02, 2017 at 03:39:18PM +0900, Minchan Kim wrote:
> > If the page is mapped and rescue in ttuo, page_mapcount(page) == 0 cannot
> > be true so page_mapcount check in ttu is enough to return SWAP_SUCCESS.
> > IOW, SWAP_MLOCK check is redundant so remove it.
> > 
> > Signed-off-by: Minchan Kim <minchan@kernel.org>
> > ---
> >  mm/rmap.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/mm/rmap.c b/mm/rmap.c
> > index 3a14013..0a48958 100644
> > --- a/mm/rmap.c
> > +++ b/mm/rmap.c
> > @@ -1523,7 +1523,7 @@ int try_to_unmap(struct page *page, enum ttu_flags flags)
> >  	else
> >  		ret = rmap_walk(page, &rwc);
> >  
> > -	if (ret != SWAP_MLOCK && !page_mapcount(page))
> > +	if (!page_mapcount(page))
> 
> Hm. I think there's bug in current code.
> It should be !total_mapcount(page) otherwise it can be false-positive if
> there's THP mapped with PTEs.

Hmm, I lost THP thesedays totally so I can miss something easily.
When I look at that, it seems every pages passed try_to_unmap is already
splited by split split_huge_page_to_list which calls freeze_page which
split pmd. So I guess it's no problem. Right?

Anyway, it's out of scope in this patch so if it's really problem,
I'd like to handle it separately.

One asking:

When we should use total_mapcount instead of page_mapcount?
If total_mapcount has some lengthy description, it would be very helpful
for one who not is faimilar with that.

> 
> And in this case ret != SWAP_MLOCK is helpful to cut down some cost.
> Althouth it should be fine to remove it, I guess.

Sure but be hard to measure it, I think. As well, later patch removes
SWAP_MLOCK.

Re: [RFC 05/11] mm: make the try_to_munlock void function

[Minchan Kim]

On Tue, Mar 07, 2017 at 06:17:47PM +0300, Kirill A. Shutemov wrote:
> On Thu, Mar 02, 2017 at 03:39:19PM +0900, Minchan Kim wrote:
> > try_to_munlock returns SWAP_MLOCK if the one of VMAs mapped
> > the page has VM_LOCKED flag. In that time, VM set PG_mlocked to
> > the page if the page is not pte-mapped THP which cannot be
> > mlocked, either.
> > 
> > With that, __munlock_isolated_page can use PageMlocked to check
> > whether try_to_munlock is successful or not without relying on
> > try_to_munlock's retval. It helps to make ttu/ttuo simple with
> > upcoming patches.
> 
> I *think* you're correct, but it took time to wrap my head around.
> We basically rely on try_to_munlock() never caller for PTE-mapped THP.
> And we don't at the moment.
> 
> It worth adding something like
> 
> 	VM_BUG_ON_PAGE(PageCompound(page) && PageDoubleMap(page), page);
> 
> into try_to_munlock().

Agree.

> 
> Otherwise looks good to me.
> 
> Will free adding my Acked-by once this nit is addressed.

Thanks for the review this part, Kirill!

> 
> -- 
>  Kirill A. Shutemov
> 
> --
> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> the body to majordomo@kvack.org.  For more info on Linux MM,
> see: http://www.linux-mm.org/ .
> Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>

Re: [RFC 06/11] mm: remove SWAP_MLOCK in ttu

[Minchan Kim]

On Tue, Mar 07, 2017 at 06:24:37PM +0300, Kirill A. Shutemov wrote:
> On Mon, Mar 06, 2017 at 11:15:08AM +0900, Minchan Kim wrote:
> > Hi Anshuman,
> > 
> > On Fri, Mar 03, 2017 at 06:06:38PM +0530, Anshuman Khandual wrote:
> > > On 03/02/2017 12:09 PM, Minchan Kim wrote:
> > > > ttu don't need to return SWAP_MLOCK. Instead, just return SWAP_FAIL
> > > > because it means the page is not-swappable so it should move to
> > > > another LRU list(active or unevictable). putback friends will
> > > > move it to right list depending on the page's LRU flag.
> > > 
> > > Right, if it cannot be swapped out there is not much difference with
> > > SWAP_FAIL once we change the callers who expected to see a SWAP_MLOCK
> > > return instead.
> > > 
> > > > 
> > > > A side effect is shrink_page_list accounts unevictable list movement
> > > > by PGACTIVATE but I don't think it corrupts something severe.
> > > 
> > > Not sure I got that, could you please elaborate on this. We will still
> > > activate the page and put it in an appropriate LRU list if it is marked
> > > mlocked ?
> > 
> > Right. putback_iactive_pages/putback_lru_page has a logic to filter
> > out unevictable pages and move them to unevictable LRU list so it
> > doesn't break LRU change behavior but the concern is until now,
> > we have accounted PGACTIVATE for only evictable LRU list page but
> > by this change, it accounts it to unevictable LRU list as well.
> > However, although I don't think it's big problem in real practice,
> > we can fix it simply with checking PG_mlocked if someone reports.
> 
> I think it's better to do this pro-actively. Let's hide both pgactivate++
> and SetPageActive() under "if (!PageMlocked())".
> SetPageActive() is not free.

I will consider it in next spin.

Thanks!

Re: [RFC 08/11] mm: make ttu's return boolean

[John Hubbard]

On 03/01/2017 10:39 PM, Minchan Kim wrote:
> try_to_unmap returns SWAP_SUCCESS or SWAP_FAIL so it's suitable for
> boolean return. This patch changes it.

Hi Minchan,

So, up until this patch, I definitely like the cleanup, because as you observed, the 
return values didn't need so many different values. However, at this point, I think 
you should stop, and keep the SWAP_SUCCESS and SWAP_FAIL (or maybe even rename them 
to UNMAP_* or TTU_RESULT_*, to match their functions' names better), because 
removing them makes the code considerably less readable.

And since this is billed as a cleanup, we care here, even though this is a minor 
point. :)

Bool return values are sometimes perfect, such as when asking a question:

    bool mode_changed = needs_modeset(crtc_state);

The above is very nice. However, for returning success or failure, bools are not as 
nice, because *usually* success == true, except when you use the errno-based system, 
in which success == 0 (which would translate to false, if you mistakenly treated it 
as a bool). That leads to the reader having to remember which system is in use, 
usually with no visual cues to help.

>
[...]
>  	if (PageSwapCache(p)) {
> @@ -971,7 +971,7 @@ static int hwpoison_user_mappings(struct page *p, unsigned long pfn,
>  		collect_procs(hpage, &tokill, flags & MF_ACTION_REQUIRED);
>
>  	ret = try_to_unmap(hpage, ttu);
> -	if (ret != SWAP_SUCCESS)
> +	if (!ret)
>  		pr_err("Memory failure: %#lx: failed to unmap page (mapcount=%d)\n",
>  		       pfn, page_mapcount(hpage));
>
> @@ -986,8 +986,7 @@ static int hwpoison_user_mappings(struct page *p, unsigned long pfn,
>  	 * any accesses to the poisoned memory.
>  	 */
>  	forcekill = PageDirty(hpage) || (flags & MF_MUST_KILL);
> -	kill_procs(&tokill, forcekill, trapno,
> -		      ret != SWAP_SUCCESS, p, pfn, flags);
> +	kill_procs(&tokill, forcekill, trapno, !ret , p, pfn, flags);

The kill_procs() invocation was a little more readable before.

>
[...]
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 170c61f..e4b74f1 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -966,7 +966,6 @@ static unsigned long shrink_page_list(struct list_head *page_list,
>  		int may_enter_fs;
>  		enum page_references references = PAGEREF_RECLAIM_CLEAN;
>  		bool dirty, writeback;
> -		int ret = SWAP_SUCCESS;
>
>  		cond_resched();
>
> @@ -1139,13 +1138,9 @@ static unsigned long shrink_page_list(struct list_head *page_list,
>  		 * processes. Try to unmap it here.
>  		 */
>  		if (page_mapped(page)) {
> -			switch (ret = try_to_unmap(page,
> -				ttu_flags | TTU_BATCH_FLUSH)) {
> -			case SWAP_FAIL:

Again: the SWAP_FAIL makes it crystal clear which case we're in.

I also wonder if UNMAP_FAIL or TTU_RESULT_FAIL is a better name?

thanks,
John Hubbard
NVIDIA

Re: [RFC 08/11] mm: make ttu's return boolean

[Minchan Kim]

Hi John,

On Tue, Mar 07, 2017 at 11:13:26PM -0800, John Hubbard wrote:
> On 03/01/2017 10:39 PM, Minchan Kim wrote:
> >try_to_unmap returns SWAP_SUCCESS or SWAP_FAIL so it's suitable for
> >boolean return. This patch changes it.
> 
> Hi Minchan,
> 
> So, up until this patch, I definitely like the cleanup, because as you
> observed, the return values didn't need so many different values. However,
> at this point, I think you should stop, and keep the SWAP_SUCCESS and
> SWAP_FAIL (or maybe even rename them to UNMAP_* or TTU_RESULT_*, to match
> their functions' names better), because removing them makes the code
> considerably less readable.
> 
> And since this is billed as a cleanup, we care here, even though this is a
> minor point. :)
> 
> Bool return values are sometimes perfect, such as when asking a question:
> 
>    bool mode_changed = needs_modeset(crtc_state);
> 
> The above is very nice. However, for returning success or failure, bools are
> not as nice, because *usually* success == true, except when you use the
> errno-based system, in which success == 0 (which would translate to false,
> if you mistakenly treated it as a bool). That leads to the reader having to
> remember which system is in use, usually with no visual cues to help.

I think it's the matter of taste.

        if (try_to_unmap(xxx))
                something
        else
                something

It's perfectly understandable to me. IOW, if try_to_unmap returns true,
it means it did unmap successfully. Otherwise, failed.

IMHO, SWAP_SUCCESS or TTU_RESULT_* seems to be an over-engineering.
If the user want it, user can do it by introducing right variable name
in his context. See below.

> 
> >
> [...]
> > 	if (PageSwapCache(p)) {
> >@@ -971,7 +971,7 @@ static int hwpoison_user_mappings(struct page *p, unsigned long pfn,
> > 		collect_procs(hpage, &tokill, flags & MF_ACTION_REQUIRED);
> >
> > 	ret = try_to_unmap(hpage, ttu);
> >-	if (ret != SWAP_SUCCESS)
> >+	if (!ret)
> > 		pr_err("Memory failure: %#lx: failed to unmap page (mapcount=%d)\n",
> > 		       pfn, page_mapcount(hpage));
> >
> >@@ -986,8 +986,7 @@ static int hwpoison_user_mappings(struct page *p, unsigned long pfn,
> > 	 * any accesses to the poisoned memory.
> > 	 */
> > 	forcekill = PageDirty(hpage) || (flags & MF_MUST_KILL);
> >-	kill_procs(&tokill, forcekill, trapno,
> >-		      ret != SWAP_SUCCESS, p, pfn, flags);
> >+	kill_procs(&tokill, forcekill, trapno, !ret , p, pfn, flags);
> 
> The kill_procs() invocation was a little more readable before.

Indeed but I think it's not a problem of try_to_unmap but ret variable name
isn't good any more. How about this?

        bool unmap_success;

        unmap_success = try_to_unmap(hpage, ttu);

        ..

        kill_procs(&tokill, forcekill, trapno, !unmap_success , p, pfn, flags);

        ..

        return unmap_success;

My point is user can introduce whatever variable name depends on his
context. No need to make return variable complicated, IMHO.

> 
> >
> [...]
> >diff --git a/mm/vmscan.c b/mm/vmscan.c
> >index 170c61f..e4b74f1 100644
> >--- a/mm/vmscan.c
> >+++ b/mm/vmscan.c
> >@@ -966,7 +966,6 @@ static unsigned long shrink_page_list(struct list_head *page_list,
> > 		int may_enter_fs;
> > 		enum page_references references = PAGEREF_RECLAIM_CLEAN;
> > 		bool dirty, writeback;
> >-		int ret = SWAP_SUCCESS;
> >
> > 		cond_resched();
> >
> >@@ -1139,13 +1138,9 @@ static unsigned long shrink_page_list(struct list_head *page_list,
> > 		 * processes. Try to unmap it here.
> > 		 */
> > 		if (page_mapped(page)) {
> >-			switch (ret = try_to_unmap(page,
> >-				ttu_flags | TTU_BATCH_FLUSH)) {
> >-			case SWAP_FAIL:
> 
> Again: the SWAP_FAIL makes it crystal clear which case we're in.

To me, I don't feel it.
To me, below is perfectly understandable.

        if (try_to_unmap())
                do something
 
That's why I think it's matter of taste. Okay, I admit I might be
biased, too so I will consider what you suggested if others votes
it.

Thanks.

> 
> I also wonder if UNMAP_FAIL or TTU_RESULT_FAIL is a better name?
> 
> thanks,
> John Hubbard
> NVIDIA
> 
> --
> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> the body to majordomo@kvack.org.  For more info on Linux MM,
> see: http://www.linux-mm.org/ .
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Re: [RFC 08/11] mm: make ttu's return boolean

[John Hubbard]

On 03/08/2017 10:37 PM, Minchan Kim wrote:
 >[...]
>
> I think it's the matter of taste.
>
>         if (try_to_unmap(xxx))
>                 something
>         else
>                 something
>
> It's perfectly understandable to me. IOW, if try_to_unmap returns true,
> it means it did unmap successfully. Otherwise, failed.
>
> IMHO, SWAP_SUCCESS or TTU_RESULT_* seems to be an over-engineering.
> If the user want it, user can do it by introducing right variable name
> in his context. See below.

I'm OK with that approach. Just something to avoid the "what does !ret mean in this 
function call" is what I was looking for...


>> [...]
>>> 	forcekill = PageDirty(hpage) || (flags & MF_MUST_KILL);
>>> -	kill_procs(&tokill, forcekill, trapno,
>>> -		      ret != SWAP_SUCCESS, p, pfn, flags);
>>> +	kill_procs(&tokill, forcekill, trapno, !ret , p, pfn, flags);
>>
>> The kill_procs() invocation was a little more readable before.
>
> Indeed but I think it's not a problem of try_to_unmap but ret variable name
> isn't good any more. How about this?
>
>         bool unmap_success;
>
>         unmap_success = try_to_unmap(hpage, ttu);
>
>         ..
>
>         kill_procs(&tokill, forcekill, trapno, !unmap_success , p, pfn, flags);
>
>         ..
>
>         return unmap_success;
>
> My point is user can introduce whatever variable name depends on his
> context. No need to make return variable complicated, IMHO.

Yes, the local variable basically achieves what I was hoping for, so sure, works for 
me.

>> [...]
>>> -			case SWAP_FAIL:
>>
>> Again: the SWAP_FAIL makes it crystal clear which case we're in.
>
> To me, I don't feel it.
> To me, below is perfectly understandable.
>
>         if (try_to_unmap())
>                 do something
>
> That's why I think it's matter of taste. Okay, I admit I might be
> biased, too so I will consider what you suggested if others votes
> it.

Yes, if it's really just a matter of taste, then not worth debating. Your change 
above is fine I think.

thanks
john h

>
> Thanks.
>