virtiofs: add logic to free up a memory range

Add logic to free up a busy memory range. Freed memory range will be
returned to free pool. Add a worker which can be started to select
and free some busy memory ranges.

Process can also steal one of its busy dax ranges if free range is not
available. I will refer it to as direct reclaim.

If free range is not available and nothing can't be stolen from same
inode, caller waits on a waitq for free range to become available.

For reclaiming a range, as of now we need to hold following locks in
specified order.

	down_write(&fi->i_mmap_sem);
	down_write(&fi->dax->sem);

We look for a free range in following order.

A. Try to get a free range.
B. If not, try direct reclaim.
C. If not, wait for a memory range to become free

Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Liu Bo <bo.liu@linux.alibaba.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/fs/fuse/virtio_fs.c b/fs/fuse/virtio_fs.c
index e25f62276050..da3ede268604 100644
--- a/fs/fuse/virtio_fs.c
+++ b/fs/fuse/virtio_fs.c
@@ -1341,6 +1341,12 @@ static void virtio_kill_sb(struct super_block *sb)
 	vfs = fc->iq.priv;
 	fsvq = &vfs->vqs[VQ_HIPRIO];
 
+	/* Stop dax worker. Soon evict_inodes() will be called which will
+	 * free all memory ranges belonging to all inodes.
+	 */
+	if (IS_ENABLED(CONFIG_FUSE_DAX))
+		fuse_dax_cancel_work(fc);
+
 	/* Stop forget queue. Soon destroy will be sent */
 	spin_lock(&fsvq->lock);
 	fsvq->connected = false;