[PATCH mmotm] add the pagefault count into memcg stats: shmem fix

[Hugh Dickins <hughd@google.com>]

mem_cgroup_count_vm_event() should update the PGMAJFAULT count for the
target mm, not for current mm (but of course they're usually the same).

We don't know the target mm in shmem_getpage(), so do it at the outer
level in shmem_fault(); and it's easier to follow if we move the
count_vm_event(PGMAJFAULT) there too.

Hah, it was using __count_vm_event() before, sneaking that update into
the unpreemptible section under info->lock: well, it comes to the same
on x86 at least, and I still think it's best to keep these together.

Signed-off-by: Hugh Dickins <hughd@google.com>
---

 mm/shmem.c |   13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

--- mmotm/mm/shmem.c	2011-05-13 14:57:45.367884578 -0700
+++ linux/mm/shmem.c	2011-05-17 10:27:19.901934756 -0700
@@ -1293,14 +1293,10 @@ repeat:
 		swappage = lookup_swap_cache(swap);
 		if (!swappage) {
 			shmem_swp_unmap(entry);
+			spin_unlock(&info->lock);
 			/* here we actually do the io */
-			if (type && !(*type & VM_FAULT_MAJOR)) {
-				__count_vm_event(PGMAJFAULT);
-				mem_cgroup_count_vm_event(current->mm,
-							  PGMAJFAULT);
+			if (type)
 				*type |= VM_FAULT_MAJOR;
-			}
-			spin_unlock(&info->lock);
 			swappage = shmem_swapin(swap, gfp, info, idx);
 			if (!swappage) {
 				spin_lock(&info->lock);
@@ -1539,7 +1535,10 @@ static int shmem_fault(struct vm_area_st
 	error = shmem_getpage(inode, vmf->pgoff, &vmf->page, SGP_CACHE, &ret);
 	if (error)
 		return ((error == -ENOMEM) ? VM_FAULT_OOM : VM_FAULT_SIGBUS);
-
+	if (ret & VM_FAULT_MAJOR) {
+		count_vm_event(PGMAJFAULT);
+		mem_cgroup_count_vm_event(vma->vm_mm, PGMAJFAULT);
+	}
 	return ret | VM_FAULT_LOCKED;
 }
 

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