mm/memcontrol: allow to uncharge page without using page->lru field

HMM pages (private or public device pages) are ZONE_DEVICE page and
thus you can not use page->lru fields of those pages. This patch
re-arrange the uncharge to allow single page to be uncharge without
modifying the lru field of the struct page.

There is no change to memcontrol logic, it is the same as it was
before this patch.

Link: http://lkml.kernel.org/r/20170817000548.32038-10-jglisse@redhat.comSigned-off-by: Jérôme Glisse <jglisse@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: Aneesh Kumar <aneesh.kumar@linux.vnet.ibm.com>
Cc: Balbir Singh <bsingharora@gmail.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: David Nellans <dnellans@nvidia.com>
Cc: Evgeny Baskakov <ebaskakov@nvidia.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Mark Hairgrove <mhairgrove@nvidia.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Cc: Sherry Cheung <SCheung@nvidia.com>
Cc: Subhash Gutti <sgutti@nvidia.com>
Cc: Bob Liu <liubo95@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/memcontrol.c

@@ -5540,63 +5540,57 @@ void mem_cgroup_cancel_charge(struct page *page, struct mem_cgroup *memcg,
 	cancel_charge(memcg, nr_pages);
 }
 
-static void uncharge_batch(struct mem_cgroup *memcg, unsigned long pgpgout,
-			   unsigned long nr_anon, unsigned long nr_file,
-			   unsigned long nr_kmem, unsigned long nr_huge,
-			   unsigned long nr_shmem, struct page *dummy_page)
+struct uncharge_gather {
+	struct mem_cgroup *memcg;
+	unsigned long pgpgout;
+	unsigned long nr_anon;
+	unsigned long nr_file;
+	unsigned long nr_kmem;
+	unsigned long nr_huge;
+	unsigned long nr_shmem;
+	struct page *dummy_page;
+};
+
+static inline void uncharge_gather_clear(struct uncharge_gather *ug)
 {
-	unsigned long nr_pages = nr_anon + nr_file + nr_kmem;
+	memset(ug, 0, sizeof(*ug));
+}
+
+static void uncharge_batch(const struct uncharge_gather *ug)
+{
+	unsigned long nr_pages = ug->nr_anon + ug->nr_file + ug->nr_kmem;
 	unsigned long flags;
 
-	if (!mem_cgroup_is_root(memcg)) {
-		page_counter_uncharge(&memcg->memory, nr_pages);
+	if (!mem_cgroup_is_root(ug->memcg)) {
+		page_counter_uncharge(&ug->memcg->memory, nr_pages);
 		if (do_memsw_account())
-			page_counter_uncharge(&memcg->memsw, nr_pages);
-		if (!cgroup_subsys_on_dfl(memory_cgrp_subsys) && nr_kmem)
-			page_counter_uncharge(&memcg->kmem, nr_kmem);
-		memcg_oom_recover(memcg);
+			page_counter_uncharge(&ug->memcg->memsw, nr_pages);
+		if (!cgroup_subsys_on_dfl(memory_cgrp_subsys) && ug->nr_kmem)
+			page_counter_uncharge(&ug->memcg->kmem, ug->nr_kmem);
+		memcg_oom_recover(ug->memcg);
 	}
 
 	local_irq_save(flags);
-	__this_cpu_sub(memcg->stat->count[MEMCG_RSS], nr_anon);
-	__this_cpu_sub(memcg->stat->count[MEMCG_CACHE], nr_file);
-	__this_cpu_sub(memcg->stat->count[MEMCG_RSS_HUGE], nr_huge);
-	__this_cpu_sub(memcg->stat->count[NR_SHMEM], nr_shmem);
-	__this_cpu_add(memcg->stat->events[PGPGOUT], pgpgout);
-	__this_cpu_add(memcg->stat->nr_page_events, nr_pages);
-	memcg_check_events(memcg, dummy_page);
+	__this_cpu_sub(ug->memcg->stat->count[MEMCG_RSS], ug->nr_anon);
+	__this_cpu_sub(ug->memcg->stat->count[MEMCG_CACHE], ug->nr_file);
+	__this_cpu_sub(ug->memcg->stat->count[MEMCG_RSS_HUGE], ug->nr_huge);
+	__this_cpu_sub(ug->memcg->stat->count[NR_SHMEM], ug->nr_shmem);
+	__this_cpu_add(ug->memcg->stat->events[PGPGOUT], ug->pgpgout);
+	__this_cpu_add(ug->memcg->stat->nr_page_events, nr_pages);
+	memcg_check_events(ug->memcg, ug->dummy_page);
 	local_irq_restore(flags);
 
-	if (!mem_cgroup_is_root(memcg))
-		css_put_many(&memcg->css, nr_pages);
+	if (!mem_cgroup_is_root(ug->memcg))
+		css_put_many(&ug->memcg->css, nr_pages);
 }
 
-static void uncharge_list(struct list_head *page_list)
+static void uncharge_page(struct page *page, struct uncharge_gather *ug)
 {
-	struct mem_cgroup *memcg = NULL;
-	unsigned long nr_shmem = 0;
-	unsigned long nr_anon = 0;
-	unsigned long nr_file = 0;
-	unsigned long nr_huge = 0;
-	unsigned long nr_kmem = 0;
-	unsigned long pgpgout = 0;
-	struct list_head *next;
-	struct page *page;
-
-	/*
-	 * Note that the list can be a single page->lru; hence the
-	 * do-while loop instead of a simple list_for_each_entry().
-	 */
-	next = page_list->next;
-	do {
-		page = list_entry(next, struct page, lru);
-		next = page->lru.next;
-
 	VM_BUG_ON_PAGE(PageLRU(page), page);
 	VM_BUG_ON_PAGE(!PageHWPoison(page) && page_count(page), page);
 
 	if (!page->mem_cgroup)
-			continue;
+		return;
 
 	/*
 	 * Nobody should be changing or seriously looking at
@@ -5604,14 +5598,12 @@ static void uncharge_list(struct list_head *page_list)
 	 * exclusive access to the page.
 	 */
 
-		if (memcg != page->mem_cgroup) {
-			if (memcg) {
-				uncharge_batch(memcg, pgpgout, nr_anon, nr_file,
-					       nr_kmem, nr_huge, nr_shmem, page);
-				pgpgout = nr_anon = nr_file = nr_kmem = 0;
-				nr_huge = nr_shmem = 0;
+	if (ug->memcg != page->mem_cgroup) {
+		if (ug->memcg) {
+			uncharge_batch(ug);
+			uncharge_gather_clear(ug);
 		}
-			memcg = page->mem_cgroup;
+		ug->memcg = page->mem_cgroup;
 	}
 
 	if (!PageKmemcg(page)) {
@@ -5619,27 +5611,48 @@ static void uncharge_list(struct list_head *page_list)
 
 		if (PageTransHuge(page)) {
 			nr_pages <<= compound_order(page);
-				nr_huge += nr_pages;
+			ug->nr_huge += nr_pages;
 		}
 		if (PageAnon(page))
-				nr_anon += nr_pages;
+			ug->nr_anon += nr_pages;
 		else {
-				nr_file += nr_pages;
+			ug->nr_file += nr_pages;
 			if (PageSwapBacked(page))
-					nr_shmem += nr_pages;
+				ug->nr_shmem += nr_pages;
 		}
-			pgpgout++;
+		ug->pgpgout++;
 	} else {
-			nr_kmem += 1 << compound_order(page);
+		ug->nr_kmem += 1 << compound_order(page);
 		__ClearPageKmemcg(page);
 	}
 
+	ug->dummy_page = page;
 	page->mem_cgroup = NULL;
+}
+
+static void uncharge_list(struct list_head *page_list)
+{
+	struct uncharge_gather ug;
+	struct list_head *next;
+
+	uncharge_gather_clear(&ug);
+
+	/*
+	 * Note that the list can be a single page->lru; hence the
+	 * do-while loop instead of a simple list_for_each_entry().
+	 */
+	next = page_list->next;
+	do {
+		struct page *page;
+
+		page = list_entry(next, struct page, lru);
+		next = page->lru.next;
+
+		uncharge_page(page, &ug);
 	} while (next != page_list);
 
-	if (memcg)
-		uncharge_batch(memcg, pgpgout, nr_anon, nr_file,
-			       nr_kmem, nr_huge, nr_shmem, page);
+	if (ug.memcg)
+		uncharge_batch(&ug);
 }
 
 /**
@@ -5651,6 +5664,8 @@ static void uncharge_list(struct list_head *page_list)
  */
 void mem_cgroup_uncharge(struct page *page)
 {
+	struct uncharge_gather ug;
+
 	if (mem_cgroup_disabled())
 		return;
 
@@ -5658,8 +5673,9 @@ void mem_cgroup_uncharge(struct page *page)
 	if (!page->mem_cgroup)
 		return;
 
-	INIT_LIST_HEAD(&page->lru);
-	uncharge_list(&page->lru);
+	uncharge_gather_clear(&ug);
+	uncharge_page(page, &ug);
+	uncharge_batch(&ug);
 }
 
 /**