Re: regression in page writeback

[Andrew Morton]

On Wed, 23 Sep 2009 08:22:20 +0800 Wu Fengguang <fengguang.wu@xxxxxxxxx> wrote:

> Jens' per-bdi writeback has another improvement. In 2.6.31, when
> superblocks A and B both have 100000 dirty pages, it will first
> exhaust A's 100000 dirty pages before going on to sync B's.

That would only be true if someone broke 2.6.31.  Did they?

SYSCALL_DEFINE0(sync)
{
	wakeup_pdflush(0);
	sync_filesystems(0);
	sync_filesystems(1);
	if (unlikely(laptop_mode))
		laptop_sync_completion();
	return 0;
}

the sync_filesystems(0) is supposed to non-blockingly start IO against
all devices.  It used to do that correctly.  But people mucked with it
so perhaps it no longer does.

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