Vivek Goyal <vgoyal@xxxxxxxxxx> writes:
> Container folks are complaining that dnf/yum issues too many sync while
> installing packages and this slows down the image build. Build
> requirement is such that they don't care if a node goes down while
> build was still going on. In that case, they will simply throw away
> unfinished layer and start new build. So they don't care about syncing
> intermediate state to the disk and hence don't want to pay the price
> associated with sync.
>
> So they are asking for mount options where they can disable sync on overlay
> mount point.
>
> They primarily seem to have two use cases.
>
> - For building images, they will mount overlay with nosync and then sync
> upper layer after unmounting overlay and reuse upper as lower for next
> layer.
>
> - For running containers, they don't seem to care about syncing upper
> layer because if node goes down, they will simply throw away upper
> layer and create a fresh one.
>
> So this patch provides a mount option "volatile" which disables all forms
> of sync. Now it is caller's responsibility to throw away upper if
> system crashes or shuts down and start fresh.
>
> With "volatile", I am seeing roughly 20% speed up in my VM where I am just
> installing emacs in an image. Installation time drops from 31 seconds to
> 25 seconds when nosync option is used. This is for the case of building on top
> of an image where all packages are already cached. That way I take
> out the network operations latency out of the measurement.
>
> Giuseppe is also looking to cut down on number of iops done on the
> disk. He is complaining that often in cloud their VMs are throttled
> if they cross the limit. This option can help them where they reduce
> number of iops (by cutting down on frequent sync and writebacks).
>
> Changes from v4:
> - Dropped support for sync=fs (Miklos)
> - Renamed "sync=off" to "volatile". (Miklos)
>
> Changes from v3:
> - Used only enums and dropped bit flags (Amir Goldstein)
> - Dropped error when conflicting sync options provided. (Amir Goldstein)
>
> Changes from v2:
> - Added helper functions (Amir Goldstein)
> - Used enums to keep sync state (Amir Goldstein)
>
> Signed-off-by: Giuseppe Scrivano <gscrivan@xxxxxxxxxx>
> Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxxxxx>
> Signed-off-by: Vivek Goyal <vgoyal@xxxxxxxxxx>
> ---
> Documentation/filesystems/overlayfs.rst | 9 +++++++++
> fs/overlayfs/copy_up.c | 12 ++++++++----
> fs/overlayfs/file.c | 10 +++++++++-
> fs/overlayfs/ovl_entry.h | 6 ++++++
> fs/overlayfs/readdir.c | 3 +++
> fs/overlayfs/super.c | 23 ++++++++++++++++++++---
> 6 files changed, 55 insertions(+), 8 deletions(-)
>
> diff --git a/Documentation/filesystems/overlayfs.rst b/Documentation/filesystems/overlayfs.rst
> index fcda5d6ba9ac..d5fc5c94560e 100644
> --- a/Documentation/filesystems/overlayfs.rst
> +++ b/Documentation/filesystems/overlayfs.rst
> @@ -563,6 +563,15 @@ This verification may cause significant overhead in some cases.
> Note: the mount options index=off,nfs_export=on are conflicting for a
> read-write mount and will result in an error.
>
> +Disable sync
> +------------
> +By default, overlay skips sync on files residing on a lower layer. It
> +is possible to skip sync operations for files on the upper layer as well
> +with the "volatile" mount option.
> +
> +"volatile" mount option disables all forms of sync from overlay, including
> +the one done at umount/remount. If system crashes or shuts down, user
> +should throw away upper directory and start fresh.
>
> Testsuite
> ---------
> diff --git a/fs/overlayfs/copy_up.c b/fs/overlayfs/copy_up.c
> index 5e0cde85bd6b..ffb8334fe94d 100644
> --- a/fs/overlayfs/copy_up.c
> +++ b/fs/overlayfs/copy_up.c
> @@ -128,7 +128,8 @@ int ovl_copy_xattr(struct dentry *old, struct dentry *new)
> return error;
> }
>
> -static int ovl_copy_up_data(struct path *old, struct path *new, loff_t len)
> +static int ovl_copy_up_data(struct ovl_fs *ofs, struct path *old,
> + struct path *new, loff_t len)
> {
> struct file *old_file;
> struct file *new_file;
> @@ -218,7 +219,7 @@ static int ovl_copy_up_data(struct path *old, struct path *new, loff_t len)
> len -= bytes;
> }
> out:
> - if (!error)
> + if (!error && ovl_should_sync(ofs))
> error = vfs_fsync(new_file, 0);
> fput(new_file);
> out_fput:
> @@ -484,6 +485,7 @@ static int ovl_link_up(struct ovl_copy_up_ctx *c)
>
> static int ovl_copy_up_inode(struct ovl_copy_up_ctx *c, struct dentry *temp)
> {
> + struct ovl_fs *ofs = OVL_FS(c->dentry->d_sb);
> int err;
>
> /*
> @@ -499,7 +501,8 @@ static int ovl_copy_up_inode(struct ovl_copy_up_ctx *c, struct dentry *temp)
> upperpath.dentry = temp;
>
> ovl_path_lowerdata(c->dentry, &datapath);
> - err = ovl_copy_up_data(&datapath, &upperpath, c->stat.size);
> + err = ovl_copy_up_data(ofs, &datapath, &upperpath,
> + c->stat.size);
> if (err)
> return err;
> }
> @@ -784,6 +787,7 @@ static bool ovl_need_meta_copy_up(struct dentry *dentry, umode_t mode,
> /* Copy up data of an inode which was copied up metadata only in the past. */
> static int ovl_copy_up_meta_inode_data(struct ovl_copy_up_ctx *c)
> {
> + struct ovl_fs *ofs = OVL_FS(c->dentry->d_sb);
> struct path upperpath, datapath;
> int err;
> char *capability = NULL;
> @@ -804,7 +808,7 @@ static int ovl_copy_up_meta_inode_data(struct ovl_copy_up_ctx *c)
> goto out;
> }
>
> - err = ovl_copy_up_data(&datapath, &upperpath, c->stat.size);
> + err = ovl_copy_up_data(ofs, &datapath, &upperpath, c->stat.size);
> if (err)
> goto out_free;
>
> diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c
> index 0d940e29d62b..3582c3ae819c 100644
> --- a/fs/overlayfs/file.c
> +++ b/fs/overlayfs/file.c
> @@ -331,6 +331,7 @@ static ssize_t ovl_write_iter(struct kiocb *iocb, struct iov_iter *iter)
> struct fd real;
> const struct cred *old_cred;
> ssize_t ret;
> + int ifl = iocb->ki_flags;
>
> if (!iov_iter_count(iter))
> return 0;
> @@ -346,11 +347,14 @@ static ssize_t ovl_write_iter(struct kiocb *iocb, struct iov_iter *iter)
> if (ret)
> goto out_unlock;
>
> + if (!ovl_should_sync(OVL_FS(inode->i_sb)))
> + ifl &= ~(IOCB_DSYNC | IOCB_SYNC);
> +
> old_cred = ovl_override_creds(file_inode(file)->i_sb);
> if (is_sync_kiocb(iocb)) {
> file_start_write(real.file);
> ret = vfs_iter_write(real.file, iter, &iocb->ki_pos,
> - ovl_iocb_to_rwf(iocb->ki_flags));
> + ovl_iocb_to_rwf(ifl));
> file_end_write(real.file);
> /* Update size */
> ovl_copyattr(ovl_inode_real(inode), inode);
> @@ -370,6 +374,7 @@ static ssize_t ovl_write_iter(struct kiocb *iocb, struct iov_iter *iter)
> real.flags = 0;
> aio_req->orig_iocb = iocb;
> kiocb_clone(&aio_req->iocb, iocb, real.file);
> + aio_req->iocb.ki_flags = ifl;
> aio_req->iocb.ki_complete = ovl_aio_rw_complete;
> ret = vfs_iocb_iter_write(real.file, &aio_req->iocb, iter);
> if (ret != -EIOCBQUEUED)
> @@ -433,6 +438,9 @@ static int ovl_fsync(struct file *file, loff_t start, loff_t end, int datasync)
> const struct cred *old_cred;
> int ret;
>
> + if (!ovl_should_sync(OVL_FS(file_inode(file)->i_sb)))
> + return 0;
> +
> ret = ovl_real_fdget_meta(file, &real, !datasync);
> if (ret)
> return ret;
> diff --git a/fs/overlayfs/ovl_entry.h b/fs/overlayfs/ovl_entry.h
> index b429c80879ee..1b5a2094df8e 100644
> --- a/fs/overlayfs/ovl_entry.h
> +++ b/fs/overlayfs/ovl_entry.h
> @@ -17,6 +17,7 @@ struct ovl_config {
> bool nfs_export;
> int xino;
> bool metacopy;
> + bool ovl_volatile;
> };
>
> struct ovl_sb {
> @@ -90,6 +91,11 @@ static inline struct ovl_fs *OVL_FS(struct super_block *sb)
> return (struct ovl_fs *)sb->s_fs_info;
> }
>
> +static inline bool ovl_should_sync(struct ovl_fs *ofs)
> +{
> + return !ofs->config.ovl_volatile;
> +}
> +
> /* private information held for every overlayfs dentry */
> struct ovl_entry {
> union {
> diff --git a/fs/overlayfs/readdir.c b/fs/overlayfs/readdir.c
> index 6918b98faeb6..2065c10ff0d1 100644
> --- a/fs/overlayfs/readdir.c
> +++ b/fs/overlayfs/readdir.c
> @@ -863,6 +863,9 @@ static int ovl_dir_fsync(struct file *file, loff_t start, loff_t end,
> if (!OVL_TYPE_UPPER(ovl_path_type(dentry)))
> return 0;
>
> + if (!ovl_should_sync(OVL_FS(dentry->d_sb)))
> + return 0;
> +
> /*
> * Need to check if we started out being a lower dir, but got copied up
> */
> diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
> index 4b38141c2985..701fc4ad822c 100644
> --- a/fs/overlayfs/super.c
> +++ b/fs/overlayfs/super.c
> @@ -264,6 +264,8 @@ static int ovl_sync_fs(struct super_block *sb, int wait)
> if (!ovl_upper_mnt(ofs))
> return 0;
>
> + if (!ovl_should_sync(ofs))
> + return 0;
> /*
> * Not called for sync(2) call or an emergency sync (SB_I_SKIP_SYNC).
> * All the super blocks will be iterated, including upper_sb.
> @@ -362,6 +364,8 @@ static int ovl_show_options(struct seq_file *m, struct dentry *dentry)
> if (ofs->config.metacopy != ovl_metacopy_def)
> seq_printf(m, ",metacopy=%s",
> ofs->config.metacopy ? "on" : "off");
> + if (ofs->config.ovl_volatile)
> + seq_printf(m, ",volatile");
> return 0;
> }
>
> @@ -376,9 +380,11 @@ static int ovl_remount(struct super_block *sb, int *flags, char *data)
>
> if (*flags & SB_RDONLY && !sb_rdonly(sb)) {
> upper_sb = ovl_upper_mnt(ofs)->mnt_sb;
> - down_read(&upper_sb->s_umount);
> - ret = sync_filesystem(upper_sb);
> - up_read(&upper_sb->s_umount);
> + if (ovl_should_sync(ofs)) {
> + down_read(&upper_sb->s_umount);
> + ret = sync_filesystem(upper_sb);
> + up_read(&upper_sb->s_umount);
> + }
> }
>
> return ret;
> @@ -411,6 +417,7 @@ enum {
> OPT_XINO_AUTO,
> OPT_METACOPY_ON,
> OPT_METACOPY_OFF,
> + OPT_VOLATILE,
> OPT_ERR,
> };
>
> @@ -429,6 +436,7 @@ static const match_table_t ovl_tokens = {
> {OPT_XINO_AUTO, "xino=auto"},
> {OPT_METACOPY_ON, "metacopy=on"},
> {OPT_METACOPY_OFF, "metacopy=off"},
> + {OPT_VOLATILE, "volatile"},
> {OPT_ERR, NULL}
> };
>
> @@ -573,6 +581,10 @@ static int ovl_parse_opt(char *opt, struct ovl_config *config)
> metacopy_opt = true;
> break;
>
> + case OPT_VOLATILE:
> + config->ovl_volatile = true;
> + break;
> +
> default:
> pr_err("unrecognized mount option \"%s\" or missing value\n",
> p);
> @@ -595,6 +607,11 @@ static int ovl_parse_opt(char *opt, struct ovl_config *config)
> config->index = false;
> }
>
> + if (!config->upperdir && config->ovl_volatile) {
> + pr_info("option \"volatile\" is meaningless in a non-upper mount, ignoring it.\n");
> + config->ovl_volatile = false;
> + }
> +
> err = ovl_parse_redirect_mode(config, config->redirect_mode);
> if (err)
> return err;
Ping.
Is there anything holding this patch?
Thanks,
Giuseppe
