From: "From: Zach Brown" <z...@zabbo.net>
This uses the new kernel aio interface to process loopback IO by
submitting concurrent direct aio. Previously loop's IO was serialized
by synchronous processing in a thread.
The aio operations specify the memory for the IO with the bio_vec arrays
directly instead of mappings of the pages.
The use of aio operations is enabled when the backing file supports the
read_iter and write_iter methods. These methods must only be added when
O_DIRECT on bio_vecs is supported.
Signed-off-by: Dave Kleikamp <dave.kleik...@oracle.com>
Cc: Zach Brown <z...@zabbo.net>
---
drivers/block/loop.c | 135 ++++++++++++++++++++++++++++++++++------------
include/uapi/linux/loop.h | 1 +
2 files changed, 103 insertions(+), 33 deletions(-)
diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index e9d594f..a221222 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -76,6 +76,7 @@
#include <linux/sysfs.h>
#include <linux/miscdevice.h>
#include <linux/falloc.h>
+#include <linux/aio.h>
#include <asm/uaccess.h>
@@ -213,6 +214,48 @@ lo_do_transfer(struct loop_device *lo, int cmd,
return lo->transfer(lo, cmd, rpage, roffs, lpage, loffs, size, rblock);
}
+#ifdef CONFIG_AIO
+static void lo_rw_aio_complete(u64 data, long res)
+{
+ struct bio *bio = (struct bio *)(uintptr_t)data;
+
+ if (res > 0)
+ res = 0;
+ else if (res < 0)
+ res = -EIO;
+
+ bio_endio(bio, res);
+}
+
+static int lo_rw_aio(struct loop_device *lo, struct bio *bio)
+{
+ struct file *file = lo->lo_backing_file;
+ struct kiocb *iocb;
+ unsigned short op;
+ struct iov_iter iter;
+ struct bio_vec *bvec;
+ size_t nr_segs;
+ loff_t pos = ((loff_t) bio->bi_sector << 9) + lo->lo_offset;
+
+ iocb = aio_kernel_alloc(GFP_NOIO);
+ if (!iocb)
+ return -ENOMEM;
+
+ if (bio_rw(bio) & WRITE)
+ op = IOCB_CMD_WRITE_ITER;
+ else
+ op = IOCB_CMD_READ_ITER;
+
+ bvec = bio_iovec_idx(bio, bio->bi_idx);
+ nr_segs = bio_segments(bio);
+ iov_iter_init_bvec(&iter, bvec, nr_segs, bvec_length(bvec, nr_segs), 0);
+ aio_kernel_init_iter(iocb, file, op, &iter, pos);
+ aio_kernel_init_callback(iocb, lo_rw_aio_complete, (u64)(uintptr_t)bio);
+
+ return aio_kernel_submit(iocb);
+}
+#endif /* CONFIG_AIO */
+
/**
* __do_lo_send_write - helper for writing data to a loop device
*
@@ -413,37 +456,6 @@ static int do_bio_filebacked(struct loop_device *lo,
struct bio *bio)
if (bio_rw(bio) == WRITE) {
struct file *file = lo->lo_backing_file;
- if (bio->bi_rw & REQ_FLUSH) {
- ret = vfs_fsync(file, 0);
- if (unlikely(ret && ret != -EINVAL)) {
- ret = -EIO;
- goto out;
- }
- }
-
- /*
- * We use punch hole to reclaim the free space used by the
- * image a.k.a. discard. However we do not support discard if
- * encryption is enabled, because it may give an attacker
- * useful information.
- */
- if (bio->bi_rw & REQ_DISCARD) {
- struct file *file = lo->lo_backing_file;
- int mode = FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE;
-
- if ((!file->f_op->fallocate) ||
- lo->lo_encrypt_key_size) {
- ret = -EOPNOTSUPP;
- goto out;
- }
- ret = file->f_op->fallocate(file, mode, pos,
- bio->bi_size);
- if (unlikely(ret && ret != -EINVAL &&
- ret != -EOPNOTSUPP))
- ret = -EIO;
- goto out;
- }
-
ret = lo_send(lo, bio, pos);
if ((bio->bi_rw & REQ_FUA) && !ret) {
@@ -454,7 +466,29 @@ static int do_bio_filebacked(struct loop_device *lo,
struct bio *bio)
} else
ret = lo_receive(lo, bio, lo->lo_blocksize, pos);
-out:
+ return ret;
+}
+
+static int lo_discard(struct loop_device *lo, struct bio *bio)
+{
+ struct file *file = lo->lo_backing_file;
+ int mode = FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE;
+ loff_t pos = ((loff_t) bio->bi_sector << 9) + lo->lo_offset;
+ int ret;
+
+ /*
+ * We use punch hole to reclaim the free space used by the
+ * image a.k.a. discard. However we do not support discard if
+ * encryption is enabled, because it may give an attacker
+ * useful information.
+ */
+
+ if ((!file->f_op->fallocate) || lo->lo_encrypt_key_size)
+ return -EOPNOTSUPP;
+
+ ret = file->f_op->fallocate(file, mode, pos, bio->bi_size);
+ if (unlikely(ret && ret != -EINVAL && ret != -EOPNOTSUPP))
+ ret = -EIO;
return ret;
}
@@ -512,7 +546,29 @@ static inline void loop_handle_bio(struct loop_device *lo,
struct bio *bio)
do_loop_switch(lo, bio->bi_private);
bio_put(bio);
} else {
- int ret = do_bio_filebacked(lo, bio);
+ int ret;
+
+ if (bio_rw(bio) == WRITE) {
+ if (bio->bi_rw & REQ_FLUSH) {
+ ret = vfs_fsync(lo->lo_backing_file, 1);
+ if (unlikely(ret && ret != -EINVAL))
+ goto out;
+ }
+ if (bio->bi_rw & REQ_DISCARD) {
+ ret = lo_discard(lo, bio);
+ goto out;
+ }
+ }
+#ifdef CONFIG_AIO
+ if (lo->lo_flags & LO_FLAGS_USE_AIO &&
+ lo->transfer == transfer_none) {
+ ret = lo_rw_aio(lo, bio);
+ if (ret == 0)
+ return;
+ } else
+#endif
+ ret = do_bio_filebacked(lo, bio);
+out:
bio_endio(bio, ret);
}
}
@@ -534,6 +590,12 @@ static int loop_thread(void *data)
struct loop_device *lo = data;
struct bio *bio;
+ /*
+ * In cases where the underlying filesystem calls balance_dirty_pages()
+ * we want less throttling to avoid lock ups trying to write dirty
+ * pages through the loop device
+ */
+ current->flags |= PF_LESS_THROTTLE;
set_user_nice(current, -20);
while (!kthread_should_stop() || !bio_list_empty(&lo->lo_bio_list)) {
@@ -854,6 +916,13 @@ static int loop_set_fd(struct loop_device *lo, fmode_t
mode,
!file->f_op->write)
lo_flags |= LO_FLAGS_READ_ONLY;
+#ifdef CONFIG_AIO
+ if (file->f_op->write_iter && file->f_op->read_iter) {
+ file->f_flags |= O_DIRECT;
+ lo_flags |= LO_FLAGS_USE_AIO;
+ }
+#endif
+
lo_blocksize = S_ISBLK(inode->i_mode) ?
inode->i_bdev->bd_block_size : PAGE_SIZE;
diff --git a/include/uapi/linux/loop.h b/include/uapi/linux/loop.h
index e0cecd2..6edc6b6 100644
--- a/include/uapi/linux/loop.h
+++ b/include/uapi/linux/loop.h
@@ -21,6 +21,7 @@ enum {
LO_FLAGS_READ_ONLY = 1,
LO_FLAGS_AUTOCLEAR = 4,
LO_FLAGS_PARTSCAN = 8,
+ LO_FLAGS_USE_AIO = 16,
};
#include <asm/posix_types.h> /* for __kernel_old_dev_t */
--
1.7.12.3
--
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