Re: [PATCH] ext2: discard block reservation on last writable file release
From: Jan Kara <jack@suse.cz>
Date: 2021-01-04 14:02:39
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 <redacted>
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
quoted hunk ↗ jump to hunk
--- 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 [off-list ref] SUSE Labs, CR