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SubjectRe: [PATCH 4/6] writeback: sync expired inodes first in background writeback
> > @@ -232,8 +232,15 @@ static void move_expired_inodes(struct l
> > while (!list_empty(delaying_queue)) {
> > inode = list_entry(delaying_queue->prev, struct inode, i_list);
> > if (expire_interval &&
> > - inode_dirtied_after(inode, older_than_this))
> > - break;
> > + inode_dirtied_after(inode, older_than_this)) {
> > + if (wbc->for_background &&
> > + list_empty(dispatch_queue) && list_empty(&tmp)) {
> > + expire_interval >>= 1;
> > + older_than_this = jiffies - expire_interval;
> > + continue;
> > + } else
> > + break;
> > + }
>
> This needs a comment.
>
> I think what it is saying is that if background flush is active but no
> inodes are old enough, consider newer inodes. This is on the assumption
> that page reclaim has encountered dirty pages and the dirty inodes are
> still too young.

Yes this should be commented. How about this one?

@@ -232,8 +232,20 @@ static void move_expired_inodes(struct l
while (!list_empty(delaying_queue)) {
inode = list_entry(delaying_queue->prev, struct inode, i_list);
if (expire_interval &&
- inode_dirtied_after(inode, older_than_this))
+ inode_dirtied_after(inode, older_than_this)) {
+ /*
+ * background writeback will start with expired inodes,
+ * and then fresh inodes. This order helps reducing
+ * the number of dirty pages reaching the end of LRU
+ * lists and cause trouble to the page reclaim.
+ */
+ if (wbc->for_background &&
+ list_empty(dispatch_queue) && list_empty(&tmp)) {
+ expire_interval = 0;
+ continue;
+ }
break;
+ }
if (sb && sb != inode->i_sb)
do_sb_sort = 1;
sb = inode->i_sb;
Thanks,
Fengguang


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