mm: memcontrol: drop @compound parameter from memcg charging API

The memcg charging API carries a boolean @compound parameter that tells
whether the page we're dealing with is a hugepage.
mem_cgroup_commit_charge() has another boolean @lrucare that indicates
whether the page needs LRU locking or not while charging.  The majority of
callsites know those parameters at compile time, which results in a lot of
naked "false, false" argument lists.  This makes for cryptic code and is a
breeding ground for subtle mistakes.

Thankfully, the huge page state can be inferred from the page itself and
doesn't need to be passed along.  This is safe because charging completes
before the page is published and somebody may split it.

Simplify the callsites by removing @compound, and let memcg infer the
state by using hpage_nr_pages() unconditionally.  That function does
PageTransHuge() to identify huge pages, which also helpfully asserts that
nobody passes in tail pages by accident.

The following patches will introduce a new charging API, best not to carry
over unnecessary weight.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Alex Shi <alex.shi@linux.alibaba.com>
Reviewed-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Reviewed-by: Shakeel Butt <shakeelb@google.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: Balbir Singh <bsingharora@gmail.com>
Link: http://lkml.kernel.org/r/20200508183105.225460-4-hannes@cmpxchg.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 15 insertions, 23 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 8f95896c5aa1..340c580f8363 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -834,7 +834,7 @@ static unsigned long memcg_events_local(struct mem_cgroup *memcg, int event)
 
 static void mem_cgroup_charge_statistics(struct mem_cgroup *memcg,
 					 struct page *page,
-					 bool compound, int nr_pages)
+					 int nr_pages)
 {
 	/*
 	 * Here, RSS means 'mapped anon' and anon's SwapCache. Shmem/tmpfs is
@@ -848,7 +848,7 @@ static void mem_cgroup_charge_statistics(struct mem_cgroup *memcg,
 			__mod_memcg_state(memcg, NR_SHMEM, nr_pages);
 	}
 
-	if (compound) {
+	if (abs(nr_pages) > 1) {
 		VM_BUG_ON_PAGE(!PageTransHuge(page), page);
 		__mod_memcg_state(memcg, MEMCG_RSS_HUGE, nr_pages);
 	}
@@ -5501,9 +5501,9 @@ static int mem_cgroup_move_account(struct page *page,
 	ret = 0;
 
 	local_irq_disable();
-	mem_cgroup_charge_statistics(to, page, compound, nr_pages);
+	mem_cgroup_charge_statistics(to, page, nr_pages);
 	memcg_check_events(to, page);
-	mem_cgroup_charge_statistics(from, page, compound, -nr_pages);
+	mem_cgroup_charge_statistics(from, page, -nr_pages);
 	memcg_check_events(from, page);
 	local_irq_enable();
 out_unlock:
@@ -6494,7 +6494,6 @@ out:
  * @mm: mm context of the victim
  * @gfp_mask: reclaim mode
  * @memcgp: charged memcg return
- * @compound: charge the page as compound or small page
  *
  * Try to charge @page to the memcg that @mm belongs to, reclaiming
  * pages according to @gfp_mask if necessary.
@@ -6507,11 +6506,10 @@ out:
  * with mem_cgroup_cancel_charge() in case page instantiation fails.
  */
 int mem_cgroup_try_charge(struct page *page, struct mm_struct *mm,
-			  gfp_t gfp_mask, struct mem_cgroup **memcgp,
-			  bool compound)
+			  gfp_t gfp_mask, struct mem_cgroup **memcgp)
 {
+	unsigned int nr_pages = hpage_nr_pages(page);
 	struct mem_cgroup *memcg = NULL;
-	unsigned int nr_pages = compound ? hpage_nr_pages(page) : 1;
 	int ret = 0;
 
 	if (mem_cgroup_disabled())
@@ -6553,13 +6551,12 @@ out:
 }
 
 int mem_cgroup_try_charge_delay(struct page *page, struct mm_struct *mm,
-			  gfp_t gfp_mask, struct mem_cgroup **memcgp,
-			  bool compound)
+			  gfp_t gfp_mask, struct mem_cgroup **memcgp)
 {
 	struct mem_cgroup *memcg;
 	int ret;
 
-	ret = mem_cgroup_try_charge(page, mm, gfp_mask, memcgp, compound);
+	ret = mem_cgroup_try_charge(page, mm, gfp_mask, memcgp);
 	memcg = *memcgp;
 	mem_cgroup_throttle_swaprate(memcg, page_to_nid(page), gfp_mask);
 	return ret;
@@ -6570,7 +6567,6 @@ int mem_cgroup_try_charge_delay(struct page *page, struct mm_struct *mm,
  * @page: page to charge
  * @memcg: memcg to charge the page to
  * @lrucare: page might be on LRU already
- * @compound: charge the page as compound or small page
  *
  * Finalize a charge transaction started by mem_cgroup_try_charge(),
  * after page->mapping has been set up.  This must happen atomically
@@ -6583,9 +6579,9 @@ int mem_cgroup_try_charge_delay(struct page *page, struct mm_struct *mm,
  * Use mem_cgroup_cancel_charge() to cancel the transaction instead.
  */
 void mem_cgroup_commit_charge(struct page *page, struct mem_cgroup *memcg,
-			      bool lrucare, bool compound)
+			      bool lrucare)
 {
-	unsigned int nr_pages = compound ? hpage_nr_pages(page) : 1;
+	unsigned int nr_pages = hpage_nr_pages(page);
 
 	VM_BUG_ON_PAGE(!page->mapping, page);
 	VM_BUG_ON_PAGE(PageLRU(page) && !lrucare, page);
@@ -6603,7 +6599,7 @@ void mem_cgroup_commit_charge(struct page *page, struct mem_cgroup *memcg,
 	commit_charge(page, memcg, lrucare);
 
 	local_irq_disable();
-	mem_cgroup_charge_statistics(memcg, page, compound, nr_pages);
+	mem_cgroup_charge_statistics(memcg, page, nr_pages);
 	memcg_check_events(memcg, page);
 	local_irq_enable();
 
@@ -6622,14 +6618,12 @@ void mem_cgroup_commit_charge(struct page *page, struct mem_cgroup *memcg,
  * mem_cgroup_cancel_charge - cancel a page charge
  * @page: page to charge
  * @memcg: memcg to charge the page to
- * @compound: charge the page as compound or small page
  *
  * Cancel a charge transaction started by mem_cgroup_try_charge().
  */
-void mem_cgroup_cancel_charge(struct page *page, struct mem_cgroup *memcg,
-		bool compound)
+void mem_cgroup_cancel_charge(struct page *page, struct mem_cgroup *memcg)
 {
-	unsigned int nr_pages = compound ? hpage_nr_pages(page) : 1;
+	unsigned int nr_pages = hpage_nr_pages(page);
 
 	if (mem_cgroup_disabled())
 		return;
@@ -6844,8 +6838,7 @@ void mem_cgroup_migrate(struct page *oldpage, struct page *newpage)
 	commit_charge(newpage, memcg, false);
 
 	local_irq_save(flags);
-	mem_cgroup_charge_statistics(memcg, newpage, PageTransHuge(newpage),
-			nr_pages);
+	mem_cgroup_charge_statistics(memcg, newpage, nr_pages);
 	memcg_check_events(memcg, newpage);
 	local_irq_restore(flags);
 }
@@ -7075,8 +7068,7 @@ void mem_cgroup_swapout(struct page *page, swp_entry_t entry)
 	 * only synchronisation we have for updating the per-CPU variables.
 	 */
 	VM_BUG_ON(!irqs_disabled());
-	mem_cgroup_charge_statistics(memcg, page, PageTransHuge(page),
-				     -nr_entries);
+	mem_cgroup_charge_statistics(memcg, page, -nr_entries);
 	memcg_check_events(memcg, page);
 
 	if (!mem_cgroup_is_root(memcg))