Re: [PATCH] [13/16] HWPOISON: The high level memory error handler in the VM v3

[Nick Piggin <npiggin@suse.de>]

On Thu, May 28, 2009 at 12:51:03PM +0200, Andi Kleen wrote:
> On Thu, May 28, 2009 at 06:33:00PM +0800, Wu Fengguang wrote:
> > > > > You haven't waited on writeback here AFAIKS, and have you
> > > > > *really* verified it is safe to call delete_from_swap_cache?
> > > > 
> > > > Good catch. I'll soon submit patches for handling the under
> > > > read/write IO pages. In this patchset they are simply ignored.
> > > 
> > > Yes, we assume the IO device does something sensible with the poisoned
> > > cache lines and aborts. Later we can likely abort IO requests in a early
> > > stage on the Linux, but that's more advanced.
> > > 
> > > The question is if we need to wait on writeback for correctness? 
> > 
> > Not necessary. Because I'm going to add a me_writeback() handler.
> 
> Ok but without it. Let's assume me_writeback() is in the future.

For correctness for what? You can't remove a page from swapcache or
pagecache under writeback because then the mm thinks that location
is not being used.

 
> I'm mainly interested in correctness (as in not crashing) of this
> version now.
> 
> Also writeback seems to be only used by nfs/afs/nilfs2, not in
> the normal case, unless I'm misreading the code. 

I don't follow. What writeback are you talking about?

> 
> The nilfs2 case seems weird, I haven't completely read that.
> 
> > Then the writeback pages simply won't reach here. And it won't
> > magically go into writeback state, since the page has been locked.
> 
> But since we take the page lock they should not be in writeback anyways,
> no?

No. PG_writeback was introduced so as to reduce page lock hold
times (most of writeback runs without page lock held).