mm: distinguish between mlocked and pinned pages

Some kernel components pin user space memory (infiniband and perf) (by
increasing the page count) and account that memory as "mlocked".

The difference between mlocking and pinning is:

A. mlocked pages are marked with PG_mlocked and are exempt from
   swapping. Page migration may move them around though.
   They are kept on a special LRU list.

B. Pinned pages cannot be moved because something needs to
   directly access physical memory. They may not be on any
   LRU list.

I recently saw an mlockalled process where mm->locked_vm became
bigger than the virtual size of the process (!) because some
memory was accounted for twice:

Once when the page was mlocked and once when the Infiniband
layer increased the refcount because it needt to pin the RDMA
memory.

This patch introduces a separate counter for pinned pages and
accounts them seperately.

Signed-off-by: Christoph Lameter <cl@linux.com>
Cc: Mike Marciniszyn <infinipath@qlogic.com>
Cc: Roland Dreier <roland@kernel.org>
Cc: Sean Hefty <sean.hefty@intel.com>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 3 insertions, 3 deletions

diff --git a/drivers/infiniband/hw/ipath/ipath_user_pages.c b/drivers/infiniband/hw/ipath/ipath_user_pages.c
index cfed5399f07..dc66c450691 100644
--- a/drivers/infiniband/hw/ipath/ipath_user_pages.c
+++ b/drivers/infiniband/hw/ipath/ipath_user_pages.c
@@ -79,7 +79,7 @@ static int __ipath_get_user_pages(unsigned long start_page, size_t num_pages,
 			goto bail_release;
 	}
 
-	current->mm->locked_vm += num_pages;
+	current->mm->pinned_vm += num_pages;
 
 	ret = 0;
 	goto bail;
@@ -178,7 +178,7 @@ void ipath_release_user_pages(struct page **p, size_t num_pages)
 
 	__ipath_release_user_pages(p, num_pages, 1);
 
-	current->mm->locked_vm -= num_pages;
+	current->mm->pinned_vm -= num_pages;
 
 	up_write(&current->mm->mmap_sem);
 }
@@ -195,7 +195,7 @@ static void user_pages_account(struct work_struct *_work)
 		container_of(_work, struct ipath_user_pages_work, work);
 
 	down_write(&work->mm->mmap_sem);
-	work->mm->locked_vm -= work->num_pages;
+	work->mm->pinned_vm -= work->num_pages;
 	up_write(&work->mm->mmap_sem);
 	mmput(work->mm);
 	kfree(work);