2021-01-02 10:20:37

by Chengguang Xu

Subject: [PATCH] ext2: discard block reservation on last writable file release

Currently reserved blocks are discarded on every writable
file release, it's not efficient for multiple writer case.

Signed-off-by: Chengguang Xu <[email protected]>
---
fs/ext2/file.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/ext2/file.c b/fs/ext2/file.c
index 96044f5dbc0e..9a19d8fe7ffd 100644
--- a/fs/ext2/file.c
+++ b/fs/ext2/file.c
@@ -141,7 +141,7 @@ static int ext2_file_mmap(struct file *file, struct vm_area_struct *vma)
*/
static int ext2_release_file (struct inode * inode, struct file * filp)
{
- if (filp->f_mode & FMODE_WRITE) {
+ if (filp->f_mode & FMODE_WRITE && (atomic_read(&inode->i_writecount) == 1)) {
mutex_lock(&EXT2_I(inode)->truncate_mutex);
ext2_discard_reservation(inode);
mutex_unlock(&EXT2_I(inode)->truncate_mutex);
--
2.18.4

2021-01-04 14:03:33

by Jan Kara

Subject: Re: [PATCH] ext2: discard block reservation on last writable file release

On Sat 02-01-21 18:18:05, Chengguang Xu wrote:
> Currently reserved blocks are discarded on every writable
> file release, it's not efficient for multiple writer case.
>
> Signed-off-by: Chengguang Xu <[email protected]>

Thanks for the patch. I agree that in principle something like this is
desirable but there's a small catch. i_writecount is also elevated from
vfs_truncate() which does not have inode open. So it can happen that
->release() gets called, sees inode->i_writecount > 1, but never gets
called again (and thus reservation is not properly released). So I prefer
to leave ext2 as is until this gets resolved - especially since ext2 fs
driver isn't really used on any performance sensitive multi-writer
workloads AFAIK (ext4 driver is usually used in such cases).

Honza

> ---
> fs/ext2/file.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/ext2/file.c b/fs/ext2/file.c
> index 96044f5dbc0e..9a19d8fe7ffd 100644
> --- a/fs/ext2/file.c
> +++ b/fs/ext2/file.c
> @@ -141,7 +141,7 @@ static int ext2_file_mmap(struct file *file, struct vm_area_struct *vma)
> */
> static int ext2_release_file (struct inode * inode, struct file * filp)
> {
> - if (filp->f_mode & FMODE_WRITE) {
> + if (filp->f_mode & FMODE_WRITE && (atomic_read(&inode->i_writecount) == 1)) {
> mutex_lock(&EXT2_I(inode)->truncate_mutex);
> ext2_discard_reservation(inode);
> mutex_unlock(&EXT2_I(inode)->truncate_mutex);
> --
> 2.18.4
>
--
Jan Kara <[email protected]>
SUSE Labs, CR