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SubjectRe: [RFC] page-writeback: move indoes from one superblock together
On Thu, Sep 24, 2009 at 02:54:20PM +0800, Li, Shaohua wrote:
> __mark_inode_dirty adds inode to wb dirty list in random order. If a disk has
> several partitions, writeback might keep spindle moving between partitions.
> To reduce the move, better write big chunk of one partition and then move to
> another. Inodes from one fs usually are in one partion, so idealy move indoes
> from one fs together should reduce spindle move. This patch tries to address
> this. Before per-bdi writeback is added, the behavior is write indoes
> from one fs first and then another, so the patch restores previous behavior.
> The loop in the patch is a bit ugly, should we add a dirty list for each
> superblock in bdi_writeback?
>
> Test in a two partition disk with attached fio script shows about 3% ~ 6%
> improvement.

Reviewed-by: Wu Fengguang <fengguang.wu@intel.com>

Good idea! The optimization looks good to me, it addresses one
weakness of per-bdi writeback.

But one problem is, Jan Kara and me are planning to remove b_io and
hence this move_expired_inodes() function. Not sure how to do this
optimization without b_io.

> Signed-off-by: Shaohua Li <shaohua.li@intel.com>
>
> diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
> index 8e1e5e1..fc87730 100644
> --- a/fs/fs-writeback.c
> +++ b/fs/fs-writeback.c
> @@ -324,13 +324,29 @@ static void move_expired_inodes(struct list_head *delaying_queue,
> struct list_head *dispatch_queue,
> unsigned long *older_than_this)
> {
> + LIST_HEAD(tmp);
> + struct list_head *pos, *node;
> + struct super_block *sb;
> + struct inode *inode;
> +
> while (!list_empty(delaying_queue)) {
> - struct inode *inode = list_entry(delaying_queue->prev,
> - struct inode, i_list);
> + inode = list_entry(delaying_queue->prev, struct inode, i_list);
> if (older_than_this &&
> inode_dirtied_after(inode, *older_than_this))
> break;
> - list_move(&inode->i_list, dispatch_queue);
> + list_move(&inode->i_list, &tmp);
> + }
> +
> + /* Move indoes from one superblock together */
> + while (!list_empty(&tmp)) {
> + inode = list_entry(tmp.prev, struct inode, i_list);
> + sb = inode->i_sb;
> + list_for_each_prev_safe(pos, node, &tmp) {

We are in spin lock, so not necessary to use the safe version?

> + struct inode *inode = list_entry(pos,

Could just reuse inode.

Thanks,
Fengguang

> + struct inode, i_list);
> + if (inode->i_sb == sb)
> + list_move(&inode->i_list, dispatch_queue);
> + }
> }
> }
>
>

Content-Description: newfio
> [global]
> runtime=120
> ioscheduler=cfq
> size=2G
> ioengine=sync
> rw=write
> file_service_type=random:256
> overwrite=1
>
> [sdb1]
> directory=/mnt/b1
> nrfiles=10
> numjobs=4
>
> [sdb2]
> directory=/mnt/b2
> nrfiles=10
> numjobs=4



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