Re: [PATCH] Memory management livelock

[Andrew Morton <akpm@linux-foundation.org>]

On Fri, 3 Oct 2008 13:47:21 +1000 Nick Piggin <nickpiggin@yahoo.com.au> wrote:

> > I expect there's no solution which avoids blocking the writers at some
> > stage.
> 
> See my other email. Something roughly like this would do the trick
> (hey, it actually boots and runs and does fix the problem too).

It needs exclusion to protect all those temp tags.  Is do_fsync()'s
i_mutex sufficient?  It's qute unobvious (and unmaintainable?) that all
the callers of this stuff are running under that lock.

> It's ugly because we don't have quite the right radix tree operations 
> yet (eg. lookup multiple tags, set tag X if tag Y was set, proper range
> lookups). But the theory is to up-front tag the pages that we need to
> get to disk.

Perhaps some callback-calling radix tree walker.

> Completely no impact or slowdown to any writers (although it does add
> 8 bytes of tags to the radix tree node... but doesn't increase memory
> footprint as such due to slab).

Can we reduce the amount of copy-n-pasting here?