A performance regression is observed since linux v4.19 when we do aio
test using fio with iodepth 128 on overlayfs. And we found that queue
depth of the device is always 1 which is unexpected.
After investigation, it is found that commit 16914e6fc7
(“ovl: add ovl_read_iter()”) and commit 2a92e07edc
(“ovl: add ovl_write_iter()”) use do_iter_readv_writev() to submit
requests to real filesystem. Async IOs are converted to sync IOs here
and cause performance regression.
So implement async IO for stacked reading and writing.
Signed-off-by: Jiufei Xue <jiufei.xue@xxxxxxxxxxxxxxxxx>
---
fs/overlayfs/file.c | 97 +++++++++++++++++++++++++++++++++++++++++-------
fs/overlayfs/overlayfs.h | 2 +
fs/overlayfs/super.c | 12 +++++-
3 files changed, 95 insertions(+), 16 deletions(-)
diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c
index e235a63..07d94e7 100644
--- a/fs/overlayfs/file.c
+++ b/fs/overlayfs/file.c
@@ -11,6 +11,14 @@
#include <linux/uaccess.h>
#include "overlayfs.h"
+struct ovl_aio_req {
+ struct kiocb iocb;
+ struct kiocb *orig_iocb;
+ struct fd fd;
+};
+
+static struct kmem_cache *ovl_aio_request_cachep;
+
static char ovl_whatisit(struct inode *inode, struct inode *realinode)
{
if (realinode != ovl_inode_upper(inode))
@@ -225,6 +233,21 @@ static rwf_t ovl_iocb_to_rwf(struct kiocb *iocb)
return flags;
}
+static void ovl_aio_rw_complete(struct kiocb *iocb, long res, long res2)
+{
+ struct ovl_aio_req *aio_req = container_of(iocb, struct ovl_aio_req, iocb);
+ struct kiocb *orig_iocb = aio_req->orig_iocb;
+
+ if (iocb->ki_flags & IOCB_WRITE)
+ file_end_write(iocb->ki_filp);
+
+ orig_iocb->ki_pos = iocb->ki_pos;
+ orig_iocb->ki_complete(orig_iocb, res, res2);
+
+ fdput(aio_req->fd);
+ kmem_cache_free(ovl_aio_request_cachep, aio_req);
+}
+
static ssize_t ovl_read_iter(struct kiocb *iocb, struct iov_iter *iter)
{
struct file *file = iocb->ki_filp;
@@ -240,14 +263,28 @@ static ssize_t ovl_read_iter(struct kiocb *iocb, struct iov_iter *iter)
return ret;
old_cred = ovl_override_creds(file_inode(file)->i_sb);
- ret = vfs_iter_read(real.file, iter, &iocb->ki_pos,
- ovl_iocb_to_rwf(iocb));
+ if (is_sync_kiocb(iocb)) {
+ ret = vfs_iter_read(real.file, iter, &iocb->ki_pos,
+ ovl_iocb_to_rwf(iocb));
+ ovl_file_accessed(file);
+ fdput(real);
+ } else {
+ struct ovl_aio_req *aio_req = kmem_cache_alloc(ovl_aio_request_cachep,
+ GFP_NOFS);
+ aio_req->fd = real;
+ aio_req->orig_iocb = iocb;
+ kiocb_clone(&aio_req->iocb, iocb, real.file);
+ aio_req->iocb.ki_complete = ovl_aio_rw_complete;
+ ret = vfs_iocb_iter_read(real.file, &aio_req->iocb, iter);
+ ovl_file_accessed(file);
+ if (ret != -EIOCBQUEUED) {
+ iocb->ki_pos = aio_req->iocb.ki_pos;
+ fdput(real);
+ kmem_cache_free(ovl_aio_request_cachep, aio_req);
+ }
+ }
revert_creds(old_cred);
- ovl_file_accessed(file);
-
- fdput(real);
-
return ret;
}
@@ -275,16 +312,32 @@ static ssize_t ovl_write_iter(struct kiocb *iocb, struct iov_iter *iter)
old_cred = ovl_override_creds(file_inode(file)->i_sb);
file_start_write(real.file);
- ret = vfs_iter_write(real.file, iter, &iocb->ki_pos,
- ovl_iocb_to_rwf(iocb));
- file_end_write(real.file);
+ if (is_sync_kiocb(iocb)) {
+ ret = vfs_iter_write(real.file, iter, &iocb->ki_pos,
+ ovl_iocb_to_rwf(iocb));
+ file_end_write(real.file);
+ /* Update size */
+ ovl_copyattr(ovl_inode_real(inode), inode);
+ fdput(real);
+ } else {
+ struct ovl_aio_req *aio_req = kmem_cache_alloc(ovl_aio_request_cachep,
+ GFP_NOFS);
+ aio_req->fd = real;
+ aio_req->orig_iocb = iocb;
+ kiocb_clone(&aio_req->iocb, iocb, real.file);
+ aio_req->iocb.ki_complete = ovl_aio_rw_complete;
+ ret = vfs_iocb_iter_write(real.file, &aio_req->iocb, iter);
+ /* Update size */
+ ovl_copyattr(ovl_inode_real(inode), inode);
+ if (ret != -EIOCBQUEUED) {
+ iocb->ki_pos = aio_req->iocb.ki_pos;
+ file_end_write(real.file);
+ fdput(real);
+ kmem_cache_free(ovl_aio_request_cachep, aio_req);
+ }
+ }
revert_creds(old_cred);
- /* Update size */
- ovl_copyattr(ovl_inode_real(inode), inode);
-
- fdput(real);
-
out_unlock:
inode_unlock(inode);
@@ -651,3 +704,19 @@ static loff_t ovl_remap_file_range(struct file *file_in, loff_t pos_in,
.copy_file_range = ovl_copy_file_range,
.remap_file_range = ovl_remap_file_range,
};
+
+int __init ovl_init_aio_request_cache(void)
+{
+ ovl_aio_request_cachep = kmem_cache_create("ovl_aio_req",
+ sizeof(struct ovl_aio_req),
+ 0, SLAB_HWCACHE_ALIGN, NULL);
+ if (!ovl_aio_request_cachep)
+ return -ENOMEM;
+
+ return 0;
+}
+
+void ovl_exit_aio_request_cache(void)
+{
+ kmem_cache_destroy(ovl_aio_request_cachep);
+}
diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
index 6934bcf..afd1631 100644
--- a/fs/overlayfs/overlayfs.h
+++ b/fs/overlayfs/overlayfs.h
@@ -416,6 +416,8 @@ struct dentry *ovl_create_real(struct inode *dir, struct dentry *newdentry,
/* file.c */
extern const struct file_operations ovl_file_operations;
+int __init ovl_init_aio_request_cache(void);
+void ovl_exit_aio_request_cache(void);
/* copy_up.c */
int ovl_copy_up(struct dentry *dentry);
diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index afbcb11..83cef1f 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -1739,9 +1739,17 @@ static int __init ovl_init(void)
if (ovl_inode_cachep == NULL)
return -ENOMEM;
+ err = ovl_init_aio_request_cache();
+ if (err) {
+ kmem_cache_destroy(ovl_inode_cachep);
+ return -ENOMEM;
+ }
+
err = register_filesystem(&ovl_fs_type);
- if (err)
+ if (err) {
kmem_cache_destroy(ovl_inode_cachep);
+ ovl_exit_aio_request_cache();
+ }
return err;
}
@@ -1756,7 +1764,7 @@ static void __exit ovl_exit(void)
*/
rcu_barrier();
kmem_cache_destroy(ovl_inode_cachep);
-
+ ovl_exit_aio_request_cache();
}
module_init(ovl_init);
--
1.8.3.1
