[PATCH 04/14] mm: shmem: provide RSS for shmem files

["Christian König" <ckoenig.leichtzumerken@gmail.com>]

This gives the OOM killer an additional hint which processes are
referencing shmem files with potentially no other accounting for them.

Signed-off-by: Christian König <christian.koenig@amd.com>
---
 mm/shmem.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/mm/shmem.c b/mm/shmem.c
index a6f565308133..b068ac5ba4bf 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -2209,6 +2209,21 @@ unsigned long shmem_get_unmapped_area(struct file *file,
 	return inflated_addr;
 }
 
+static long shmem_file_rss(struct file *file)
+{
+	struct inode *inode = file_inode(file);
+	unsigned long nrpages;
+
+	/* Only account shmem files which aren't part of any fs */
+	if (atomic_read(&inode->i_count) > 1)
+		return 0;
+
+	xa_lock(&file->f_mapping->i_pages);
+	nrpages = file->f_mapping->nrpages;
+	xa_unlock(&file->f_mapping->i_pages);
+	return nrpages;
+}
+
 #ifdef CONFIG_NUMA
 static int shmem_set_policy(struct vm_area_struct *vma, struct mempolicy *mpol)
 {
@@ -3811,6 +3826,7 @@ EXPORT_SYMBOL(shmem_aops);
 static const struct file_operations shmem_file_operations = {
 	.mmap		= shmem_mmap,
 	.get_unmapped_area = shmem_get_unmapped_area,
+	.file_rss	= shmem_file_rss,
 #ifdef CONFIG_TMPFS
 	.llseek		= shmem_file_llseek,
 	.read_iter	= shmem_file_read_iter,
-- 
2.25.1