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 71f613cf4a85..82eec7c7b4bb 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;