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Date: Fri, 23 Jul 2010 20:17:51 +0200
From: Jan Kara <jack@...e.cz>
To: Wu Fengguang <fengguang.wu@...el.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Dave Chinner <david@...morbit.com>, Jan Kara <jack@...e.cz>,
Christoph Hellwig <hch@...radead.org>,
Mel Gorman <mel@....ul.ie>,
Chris Mason <chris.mason@...cle.com>,
Jens Axboe <jens.axboe@...cle.com>,
LKML <linux-kernel@...r.kernel.org>,
linux-fsdevel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 2/6] writeback: the kupdate expire timestamp should be
a moving target
On Thu 22-07-10 13:09:30, Wu Fengguang wrote:
> Dynamicly compute the dirty expire timestamp at queue_io() time.
> Also remove writeback_control.older_than_this which is no longer used.
>
> writeback_control.older_than_this used to be determined at entrance to
> the kupdate writeback work. This _static_ timestamp may go stale if the
> kupdate work runs on and on. The flusher may then stuck with some old
> busy inodes, never considering newly expired inodes thereafter.
This seems to make sense. The patch looks fine as well.
Acked-by: Jan Kara <jack@...e.cz>
Honza
>
> This has two possible problems:
>
> - It is unfair for a large dirty inode to delay (for a long time) the
> writeback of small dirty inodes.
>
> - As time goes by, the large and busy dirty inode may contain only
> _freshly_ dirtied pages. Ignoring newly expired dirty inodes risks
> delaying the expired dirty pages to the end of LRU lists, triggering
> the very bad pageout(). Neverthless this patch merely addresses part
> of the problem.
>
> CC: Jan Kara <jack@...e.cz>
> Signed-off-by: Wu Fengguang <fengguang.wu@...el.com>
> ---
> fs/fs-writeback.c | 24 +++++++++---------------
> include/linux/writeback.h | 2 --
> include/trace/events/writeback.h | 6 +-----
> mm/backing-dev.c | 1 -
> mm/page-writeback.c | 1 -
> 5 files changed, 10 insertions(+), 24 deletions(-)
>
> --- linux-next.orig/fs/fs-writeback.c 2010-07-21 22:20:01.000000000 +0800
> +++ linux-next/fs/fs-writeback.c 2010-07-22 11:23:27.000000000 +0800
> @@ -216,16 +216,23 @@ static void move_expired_inodes(struct l
> struct list_head *dispatch_queue,
> struct writeback_control *wbc)
> {
> + unsigned long expire_interval = 0;
> + unsigned long older_than_this;
> LIST_HEAD(tmp);
> struct list_head *pos, *node;
> struct super_block *sb = NULL;
> struct inode *inode;
> int do_sb_sort = 0;
>
> + if (wbc->for_kupdate) {
> + expire_interval = msecs_to_jiffies(dirty_expire_interval * 10);
> + older_than_this = jiffies - expire_interval;
> + }
> +
> while (!list_empty(delaying_queue)) {
> inode = list_entry(delaying_queue->prev, struct inode, i_list);
> - if (wbc->older_than_this &&
> - inode_dirtied_after(inode, *wbc->older_than_this))
> + if (expire_interval &&
> + inode_dirtied_after(inode, older_than_this))
> break;
> if (sb && sb != inode->i_sb)
> do_sb_sort = 1;
> @@ -583,29 +590,19 @@ static inline bool over_bground_thresh(v
> * Try to run once per dirty_writeback_interval. But if a writeback event
> * takes longer than a dirty_writeback_interval interval, then leave a
> * one-second gap.
> - *
> - * older_than_this takes precedence over nr_to_write. So we'll only write back
> - * all dirty pages if they are all attached to "old" mappings.
> */
> static long wb_writeback(struct bdi_writeback *wb,
> struct wb_writeback_work *work)
> {
> struct writeback_control wbc = {
> .sync_mode = work->sync_mode,
> - .older_than_this = NULL,
> .for_kupdate = work->for_kupdate,
> .for_background = work->for_background,
> .range_cyclic = work->range_cyclic,
> };
> - unsigned long oldest_jif;
> long wrote = 0;
> struct inode *inode;
>
> - if (wbc.for_kupdate) {
> - wbc.older_than_this = &oldest_jif;
> - oldest_jif = jiffies -
> - msecs_to_jiffies(dirty_expire_interval * 10);
> - }
> if (!wbc.range_cyclic) {
> wbc.range_start = 0;
> wbc.range_end = LLONG_MAX;
> @@ -998,9 +995,6 @@ EXPORT_SYMBOL(__mark_inode_dirty);
> * Write out a superblock's list of dirty inodes. A wait will be performed
> * upon no inodes, all inodes or the final one, depending upon sync_mode.
> *
> - * If older_than_this is non-NULL, then only write out inodes which
> - * had their first dirtying at a time earlier than *older_than_this.
> - *
> * If `bdi' is non-zero then we're being asked to writeback a specific queue.
> * This function assumes that the blockdev superblock's inodes are backed by
> * a variety of queues, so all inodes are searched. For other superblocks,
> --- linux-next.orig/include/linux/writeback.h 2010-07-21 22:20:02.000000000 +0800
> +++ linux-next/include/linux/writeback.h 2010-07-22 11:23:27.000000000 +0800
> @@ -28,8 +28,6 @@ enum writeback_sync_modes {
> */
> struct writeback_control {
> enum writeback_sync_modes sync_mode;
> - unsigned long *older_than_this; /* If !NULL, only write back inodes
> - older than this */
> unsigned long wb_start; /* Time writeback_inodes_wb was
> called. This is needed to avoid
> extra jobs and livelock */
> --- linux-next.orig/include/trace/events/writeback.h 2010-07-21 22:20:02.000000000 +0800
> +++ linux-next/include/trace/events/writeback.h 2010-07-22 11:23:27.000000000 +0800
> @@ -100,7 +100,6 @@ DECLARE_EVENT_CLASS(wbc_class,
> __field(int, for_reclaim)
> __field(int, range_cyclic)
> __field(int, more_io)
> - __field(unsigned long, older_than_this)
> __field(long, range_start)
> __field(long, range_end)
> ),
> @@ -115,14 +114,12 @@ DECLARE_EVENT_CLASS(wbc_class,
> __entry->for_reclaim = wbc->for_reclaim;
> __entry->range_cyclic = wbc->range_cyclic;
> __entry->more_io = wbc->more_io;
> - __entry->older_than_this = wbc->older_than_this ?
> - *wbc->older_than_this : 0;
> __entry->range_start = (long)wbc->range_start;
> __entry->range_end = (long)wbc->range_end;
> ),
>
> TP_printk("bdi %s: towrt=%ld skip=%ld mode=%d kupd=%d "
> - "bgrd=%d reclm=%d cyclic=%d more=%d older=0x%lx "
> + "bgrd=%d reclm=%d cyclic=%d more=%d "
> "start=0x%lx end=0x%lx",
> __entry->name,
> __entry->nr_to_write,
> @@ -133,7 +130,6 @@ DECLARE_EVENT_CLASS(wbc_class,
> __entry->for_reclaim,
> __entry->range_cyclic,
> __entry->more_io,
> - __entry->older_than_this,
> __entry->range_start,
> __entry->range_end)
> )
> --- linux-next.orig/mm/page-writeback.c 2010-07-21 22:20:02.000000000 +0800
> +++ linux-next/mm/page-writeback.c 2010-07-21 22:20:03.000000000 +0800
> @@ -482,7 +482,6 @@ static void balance_dirty_pages(struct a
> for (;;) {
> struct writeback_control wbc = {
> .sync_mode = WB_SYNC_NONE,
> - .older_than_this = NULL,
> .nr_to_write = write_chunk,
> .range_cyclic = 1,
> };
> --- linux-next.orig/mm/backing-dev.c 2010-07-22 11:23:34.000000000 +0800
> +++ linux-next/mm/backing-dev.c 2010-07-22 11:23:39.000000000 +0800
> @@ -271,7 +271,6 @@ static void bdi_flush_io(struct backing_
> {
> struct writeback_control wbc = {
> .sync_mode = WB_SYNC_NONE,
> - .older_than_this = NULL,
> .range_cyclic = 1,
> .nr_to_write = 1024,
> };
>
>
> --
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--
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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