seq_file: account everything to kmemcg

All it takes to open a file and read 1 byte from it.

seq_file will be allocated along with any private allocations, and more
importantly seq file buffer which is 1 page by default.

Link: http://lkml.kernel.org/r/20180310085252.GB17121@avx2
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Glauber Costa <glommer@gmail.com>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/seq_file.c

@@ -29,7 +29,7 @@ static void seq_set_overflow(struct seq_file *m)
 
 static void *seq_buf_alloc(unsigned long size)
 {
-	return kvmalloc(size, GFP_KERNEL);
+	return kvmalloc(size, GFP_KERNEL_ACCOUNT);
 }
 
 /**
@@ -566,7 +566,7 @@ static void single_stop(struct seq_file *p, void *v)
 int single_open(struct file *file, int (*show)(struct seq_file *, void *),
 		void *data)
 {
-	struct seq_operations *op = kmalloc(sizeof(*op), GFP_KERNEL);
+	struct seq_operations *op = kmalloc(sizeof(*op), GFP_KERNEL_ACCOUNT);
 	int res = -ENOMEM;
 
 	if (op) {
@@ -628,7 +628,7 @@ void *__seq_open_private(struct file *f, const struct seq_operations *ops,
 	void *private;
 	struct seq_file *seq;
 
-	private = kzalloc(psize, GFP_KERNEL);
+	private = kzalloc(psize, GFP_KERNEL_ACCOUNT);
 	if (private == NULL)
 		goto out;
 
@@ -1112,5 +1112,5 @@ EXPORT_SYMBOL(seq_hlist_next_percpu);
 
 void __init seq_file_init(void)
 {
-	seq_file_cache = KMEM_CACHE(seq_file, SLAB_PANIC);
+	seq_file_cache = KMEM_CACHE(seq_file, SLAB_ACCOUNT|SLAB_PANIC);
 }