On Mon, 2007-12-10 at 18:02 -0800, Michael Rubin wrote:
> From: Michael Rubin <[email protected]>
>
> Fixing a bug where writing to large files while concurrently writing to
> smaller ones creates a situation where writeback cannot keep up with the
> traffic and memory baloons until the we hit the threshold watermark. This
> can result in surprising latency spikes when syncing. This latency
> can take minutes on large memory systems. Upon request I can provide
> a test to reproduce this situation.
The part I miss here is the rationale on _how_ you solve the problem.
The patch itself is simple enough, but I've been staring at this code
for a while now, and I'm just not getting it.
> The only concern I have is that this makes the wb_kupdate slightly more
> agressive. I am not sure it is enough to cause any problems. I think
> there is enough checks to throttle the background activity.
>
> Feng also the one line change that you recommended here
> http://marc.info/?l=linux-kernel&m=119629655402153&w=2 had no effect.
>
> Signed-off-by: Michael Rubin <[email protected]>
> ---
> Index: 2624rc3_feng/fs/fs-writeback.c
> ===================================================================
> --- 2624rc3_feng.orig/fs/fs-writeback.c 2007-11-29 14:44:24.000000000 -0800
> +++ 2624rc3_feng/fs/fs-writeback.c 2007-12-10 17:21:45.000000000 -0800
> @@ -408,8 +408,7 @@ sync_sb_inodes(struct super_block *sb, s
> {
> const unsigned long start = jiffies; /* livelock avoidance */
>
> - if (!wbc->for_kupdate || list_empty(&sb->s_io))
> - queue_io(sb, wbc->older_than_this);
> + queue_io(sb, wbc->older_than_this);
>
> while (!list_empty(&sb->s_io)) {
> struct inode *inode = list_entry(sb->s_io.prev,
> Index: 2624rc3_feng/mm/page-writeback.c
> ===================================================================
> --- 2624rc3_feng.orig/mm/page-writeback.c 2007-11-16 21:16:36.000000000 -0800
> +++ 2624rc3_feng/mm/page-writeback.c 2007-12-10 17:37:17.000000000 -0800
> @@ -638,7 +638,7 @@ static void wb_kupdate(unsigned long arg
> wbc.nr_to_write = MAX_WRITEBACK_PAGES;
> writeback_inodes(&wbc);
> if (wbc.nr_to_write > 0) {
> - if (wbc.encountered_congestion || wbc.more_io)
> + if (wbc.encountered_congestion)
> congestion_wait(WRITE, HZ/10);
> else
> break; /* All the old data is written */
--
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