[PATCH 1/2 v4][rfc] shmem: provide vm_ops when also providing a mem policy

[Nathan Zimmer <nzimmer@xxxxxxx>]

Updating shmem_get_policy to use the vma_policy if provided.
This is to allows us to safely provide shmem_vm_ops to the vma when the vm_file
has not been setup which is the case on the pseudo vmas.


Cc: Christoph Lameter <cl@xxxxxxxxx>
Cc: Nick Piggin <npiggin@xxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Lee Schermerhorn <lee.schermerhorn@xxxxxx>
Cc: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Signed-off-by: Nathan T Zimmer <nzimmer@xxxxxxx>
---

 mm/shmem.c |   18 +++++++++++++++---
 1 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/mm/shmem.c b/mm/shmem.c
index a15a466..9bd599b 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -921,8 +921,11 @@ static struct page *shmem_swapin(swp_entry_t swap, gfp_t gfp,
 	/* Create a pseudo vma that just contains the policy */
 	pvma.vm_start = 0;
 	pvma.vm_pgoff = index;
-	pvma.vm_ops = NULL;
 	pvma.vm_policy = spol;
+	if( pvma.vm_policy )
+		pvma.vm_ops = &shmem_vm_ops;
+	else
+		pvma.vm_ops = NULL;
 	return swapin_readahead(swap, gfp, &pvma, 0);
 }
 
@@ -934,8 +937,11 @@ static struct page *shmem_alloc_page(gfp_t gfp,
 	/* Create a pseudo vma that just contains the policy */
 	pvma.vm_start = 0;
 	pvma.vm_pgoff = index;
-	pvma.vm_ops = NULL;
 	pvma.vm_policy = mpol_shared_policy_lookup(&info->policy, index);
+	if( pvma.vm_policy )
+		pvma.vm_ops = &shmem_vm_ops;
+	else
+		pvma.vm_ops = NULL;
 
 	/*
 	 * alloc_page_vma() will drop the shared policy reference
@@ -1296,8 +1302,14 @@ static int shmem_set_policy(struct vm_area_struct *vma, struct mempolicy *mpol)
 static struct mempolicy *shmem_get_policy(struct vm_area_struct *vma,
 					  unsigned long addr)
 {
-	struct inode *inode = vma->vm_file->f_path.dentry->d_inode;
 	pgoff_t index;
+	struct inode *inode;
+
+	// If the vma knows what policy it wants use that one.
+	if (vma->vm_policy)
+		return vma->vm_policy;
+
+	inode = vma->vm_file->f_path.dentry->d_inode;
 
 	index = ((addr - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
 	return mpol_shared_policy_lookup(&SHMEM_I(inode)->policy, index);
--
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