[patch 096/131] mm: memcontrol: drop unused try/commit/cancel charge API

[Andrew Morton <akpm@linux-foundation.org>]

From: Johannes Weiner <hannes@cmpxchg.org>
Subject: mm: memcontrol: drop unused try/commit/cancel charge API

There are no more users. RIP in peace.

[arnd@arndb.de: fix an unused-function warning]
  Link: http://lkml.kernel.org/r/20200528095640.151454-1-arnd@arndb.de
Link: http://lkml.kernel.org/r/20200508183105.225460-14-hannes@cmpxchg.org
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Alex Shi <alex.shi@linux.alibaba.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Roman Gushchin <guro@fb.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Balbir Singh <bsingharora@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 include/linux/memcontrol.h |   36 ---------
 mm/memcontrol.c            |  128 ++++-------------------------------
 2 files changed, 17 insertions(+), 147 deletions(-)

--- a/include/linux/memcontrol.h~mm-memcontrol-drop-unused-try-commit-cancel-charge-api
+++ a/include/linux/memcontrol.h
@@ -355,14 +355,6 @@ static inline unsigned long mem_cgroup_p
 enum mem_cgroup_protection mem_cgroup_protected(struct mem_cgroup *root,
 						struct mem_cgroup *memcg);
 
-int mem_cgroup_try_charge(struct page *page, struct mm_struct *mm,
-			  gfp_t gfp_mask, struct mem_cgroup **memcgp);
-int mem_cgroup_try_charge_delay(struct page *page, struct mm_struct *mm,
-			  gfp_t gfp_mask, struct mem_cgroup **memcgp);
-void mem_cgroup_commit_charge(struct page *page, struct mem_cgroup *memcg,
-			      bool lrucare);
-void mem_cgroup_cancel_charge(struct page *page, struct mem_cgroup *memcg);
-
 int mem_cgroup_charge(struct page *page, struct mm_struct *mm, gfp_t gfp_mask,
 		      bool lrucare);
 
@@ -846,34 +838,6 @@ static inline enum mem_cgroup_protection
 	return MEMCG_PROT_NONE;
 }
 
-static inline int mem_cgroup_try_charge(struct page *page, struct mm_struct *mm,
-					gfp_t gfp_mask,
-					struct mem_cgroup **memcgp)
-{
-	*memcgp = NULL;
-	return 0;
-}
-
-static inline int mem_cgroup_try_charge_delay(struct page *page,
-					      struct mm_struct *mm,
-					      gfp_t gfp_mask,
-					      struct mem_cgroup **memcgp)
-{
-	*memcgp = NULL;
-	return 0;
-}
-
-static inline void mem_cgroup_commit_charge(struct page *page,
-					    struct mem_cgroup *memcg,
-					    bool lrucare)
-{
-}
-
-static inline void mem_cgroup_cancel_charge(struct page *page,
-					    struct mem_cgroup *memcg)
-{
-}
-
 static inline int mem_cgroup_charge(struct page *page, struct mm_struct *mm,
 				    gfp_t gfp_mask, bool lrucare)
 {
--- a/mm/memcontrol.c~mm-memcontrol-drop-unused-try-commit-cancel-charge-api
+++ a/mm/memcontrol.c
@@ -2641,6 +2641,7 @@ done_restock:
 	return 0;
 }
 
+#if defined(CONFIG_MEMCG_KMEM) || defined(CONFIG_MMU)
 static void cancel_charge(struct mem_cgroup *memcg, unsigned int nr_pages)
 {
 	if (mem_cgroup_is_root(memcg))
@@ -2652,6 +2653,7 @@ static void cancel_charge(struct mem_cgr
 
 	css_put_many(&memcg->css, nr_pages);
 }
+#endif
 
 static void lock_page_lru(struct page *page, int *isolated)
 {
@@ -6499,29 +6501,26 @@ out:
 }
 
 /**
- * mem_cgroup_try_charge - try charging a page
+ * mem_cgroup_charge - charge a newly allocated page to a cgroup
  * @page: page to charge
  * @mm: mm context of the victim
  * @gfp_mask: reclaim mode
- * @memcgp: charged memcg return
+ * @lrucare: page might be on the LRU already
  *
  * Try to charge @page to the memcg that @mm belongs to, reclaiming
  * pages according to @gfp_mask if necessary.
  *
- * Returns 0 on success, with *@memcgp pointing to the charged memcg.
- * Otherwise, an error code is returned.
- *
- * After page->mapping has been set up, the caller must finalize the
- * charge with mem_cgroup_commit_charge().  Or abort the transaction
- * with mem_cgroup_cancel_charge() in case page instantiation fails.
+ * Returns 0 on success. Otherwise, an error code is returned.
  */
-int mem_cgroup_try_charge(struct page *page, struct mm_struct *mm,
-			  gfp_t gfp_mask, struct mem_cgroup **memcgp)
+int mem_cgroup_charge(struct page *page, struct mm_struct *mm, gfp_t gfp_mask,
+		      bool lrucare)
 {
 	unsigned int nr_pages = hpage_nr_pages(page);
 	struct mem_cgroup *memcg = NULL;
 	int ret = 0;
 
+	VM_BUG_ON_PAGE(PageLRU(page) && !lrucare, page);
+
 	if (mem_cgroup_disabled())
 		goto out;
 
@@ -6553,56 +6552,8 @@ int mem_cgroup_try_charge(struct page *p
 		memcg = get_mem_cgroup_from_mm(mm);
 
 	ret = try_charge(memcg, gfp_mask, nr_pages);
-
-	css_put(&memcg->css);
-out:
-	*memcgp = memcg;
-	return ret;
-}
-
-int mem_cgroup_try_charge_delay(struct page *page, struct mm_struct *mm,
-			  gfp_t gfp_mask, struct mem_cgroup **memcgp)
-{
-	int ret;
-
-	ret = mem_cgroup_try_charge(page, mm, gfp_mask, memcgp);
-	if (*memcgp)
-		cgroup_throttle_swaprate(page, gfp_mask);
-	return ret;
-}
-
-/**
- * mem_cgroup_commit_charge - commit a page charge
- * @page: page to charge
- * @memcg: memcg to charge the page to
- * @lrucare: page might be on LRU already
- *
- * Finalize a charge transaction started by mem_cgroup_try_charge(),
- * after page->mapping has been set up.  This must happen atomically
- * as part of the page instantiation, i.e. under the page table lock
- * for anonymous pages, under the page lock for page and swap cache.
- *
- * In addition, the page must not be on the LRU during the commit, to
- * prevent racing with task migration.  If it might be, use @lrucare.
- *
- * Use mem_cgroup_cancel_charge() to cancel the transaction instead.
- */
-void mem_cgroup_commit_charge(struct page *page, struct mem_cgroup *memcg,
-			      bool lrucare)
-{
-	unsigned int nr_pages = hpage_nr_pages(page);
-
-	VM_BUG_ON_PAGE(PageLRU(page) && !lrucare, page);
-
-	if (mem_cgroup_disabled())
-		return;
-	/*
-	 * Swap faults will attempt to charge the same page multiple
-	 * times.  But reuse_swap_page() might have removed the page
-	 * from swapcache already, so we can't check PageSwapCache().
-	 */
-	if (!memcg)
-		return;
+	if (ret)
+		goto out_put;
 
 	commit_charge(page, memcg, lrucare);
 
@@ -6620,55 +6571,11 @@ void mem_cgroup_commit_charge(struct pag
 		 */
 		mem_cgroup_uncharge_swap(entry, nr_pages);
 	}
-}
 
-/**
- * mem_cgroup_cancel_charge - cancel a page charge
- * @page: page to charge
- * @memcg: memcg to charge the page to
- *
- * Cancel a charge transaction started by mem_cgroup_try_charge().
- */
-void mem_cgroup_cancel_charge(struct page *page, struct mem_cgroup *memcg)
-{
-	unsigned int nr_pages = hpage_nr_pages(page);
-
-	if (mem_cgroup_disabled())
-		return;
-	/*
-	 * Swap faults will attempt to charge the same page multiple
-	 * times.  But reuse_swap_page() might have removed the page
-	 * from swapcache already, so we can't check PageSwapCache().
-	 */
-	if (!memcg)
-		return;
-
-	cancel_charge(memcg, nr_pages);
-}
-
-/**
- * mem_cgroup_charge - charge a newly allocated page to a cgroup
- * @page: page to charge
- * @mm: mm context of the victim
- * @gfp_mask: reclaim mode
- * @lrucare: page might be on the LRU already
- *
- * Try to charge @page to the memcg that @mm belongs to, reclaiming
- * pages according to @gfp_mask if necessary.
- *
- * Returns 0 on success. Otherwise, an error code is returned.
- */
-int mem_cgroup_charge(struct page *page, struct mm_struct *mm, gfp_t gfp_mask,
-		      bool lrucare)
-{
-	struct mem_cgroup *memcg;
-	int ret;
-
-	ret = mem_cgroup_try_charge(page, mm, gfp_mask, &memcg);
-	if (ret)
-		return ret;
-	mem_cgroup_commit_charge(page, memcg, lrucare);
-	return 0;
+out_put:
+	css_put(&memcg->css);
+out:
+	return ret;
 }
 
 struct uncharge_gather {
@@ -6773,8 +6680,7 @@ static void uncharge_list(struct list_he
  * mem_cgroup_uncharge - uncharge a page
  * @page: page to uncharge
  *
- * Uncharge a page previously charged with mem_cgroup_try_charge() and
- * mem_cgroup_commit_charge().
+ * Uncharge a page previously charged with mem_cgroup_charge().
  */
 void mem_cgroup_uncharge(struct page *page)
 {
@@ -6797,7 +6703,7 @@ void mem_cgroup_uncharge(struct page *pa
  * @page_list: list of pages to uncharge
  *
  * Uncharge a list of pages previously charged with
- * mem_cgroup_try_charge() and mem_cgroup_commit_charge().
+ * mem_cgroup_charge().
  */
 void mem_cgroup_uncharge_list(struct list_head *page_list)
 {
_