mm: introduce mm_populate() for populating new vmas

When creating new mappings using the MAP_POPULATE / MAP_LOCKED flags (or
with MCL_FUTURE in effect), we want to populate the pages within the
newly created vmas.  This may take a while as we may have to read pages
from disk, so ideally we want to do this outside of the write-locked
mmap_sem region.

This change introduces mm_populate(), which is used to defer populating
such mappings until after the mmap_sem write lock has been released.
This is implemented as a generalization of the former do_mlock_pages(),
which accomplished the same task but was using during mlock() /
mlockall().

Signed-off-by: Michel Lespinasse <walken@google.com>
Reported-by: Andy Lutomirski <luto@amacapital.net>
Acked-by: Rik van Riel <riel@redhat.com>
Tested-by: Andy Lutomirski <luto@amacapital.net>
Cc: Greg Ungerer <gregungerer@westnet.com.au>
Cc: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 5 insertions, 1 deletions

diff --git a/fs/aio.c b/fs/aio.c
index 71f613cf4a8..82eec7c7b4b 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -103,6 +103,7 @@ static int aio_setup_ring(struct kioctx *ctx)
 	unsigned nr_events = ctx->max_reqs;
 	unsigned long size;
 	int nr_pages;
+	bool populate;
 
 	/* Compensate for the ring buffer's head/tail overlap entry */
 	nr_events += 2;	/* 1 is required, 2 for good luck */
@@ -129,7 +130,8 @@ static int aio_setup_ring(struct kioctx *ctx)
 	down_write(&ctx->mm->mmap_sem);
 	info->mmap_base = do_mmap_pgoff(NULL, 0, info->mmap_size, 
 					PROT_READ|PROT_WRITE,
-					MAP_ANONYMOUS|MAP_PRIVATE, 0);
+					MAP_ANONYMOUS|MAP_PRIVATE, 0,
+					&populate);
 	if (IS_ERR((void *)info->mmap_base)) {
 		up_write(&ctx->mm->mmap_sem);
 		info->mmap_size = 0;
@@ -147,6 +149,8 @@ static int aio_setup_ring(struct kioctx *ctx)
 		aio_free_ring(ctx);
 		return -EAGAIN;
 	}
+	if (populate)
+		mm_populate(info->mmap_base, info->mmap_size);
 
 	ctx->user_id = info->mmap_base;