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

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Date:	Tue, 2 Jun 2009 15:41:26 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Nick Piggin <npiggin@...e.de>
Cc:	Andi Kleen <andi@...stfloor.org>,
	Wu Fengguang <fengguang.wu@...el.com>,
	"hugh@...itas.com" <hugh@...itas.com>,
	"riel@...hat.com" <riel@...hat.com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"chris.mason@...cle.com" <chris.mason@...cle.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [PATCH] [13/16] HWPOISON: The high level memory error handler in the VM v3

On Tue, Jun 02, 2009 at 03:24:41PM +0200, Nick Piggin wrote:
> On Tue, Jun 02, 2009 at 03:25:38PM +0200, Andi Kleen wrote:
> > On Tue, Jun 02, 2009 at 02:57:13PM +0200, Nick Piggin wrote:
> > > > > not a big deal and just avoids duplicating code. I attached an
> > > > > (untested) patch.
> > > > 
> > > > Thanks. But the function in the patch is not doing the same what
> > > > the me_pagecache_clean/dirty are doing. For once there is no error
> > > > checking, as in the second try_to_release_page()
> > > > 
> > > > Then it doesn't do all the IO error and missing mapping handling.
> > > 
> > > Obviously I don't mean just use that single call for the entire
> > > handler. You can set the EIO bit or whatever you like. The
> > > "error handling" you have there also seems strange. You could
> > > retain it, but the page is assured to be removed from pagecache.
> > 
> > The reason this code double checks is that someone could have 
> > a reference (remember we can come in any time) we cannot kill immediately.
> 
> Can't kill what? The page is gone from pagecache. It may remain
> other kernel references, but I don't see why this code will
> consider this as a failure (and not, for example, a raised error
> count).

It's a failure because the page was still used and not successfully
isolated.

> +        * remove_from_page_cache assumes (mapping && !mapped)
> +        */
> +       if (page_mapping(p) && !page_mapped(p)) {

Ok you're right. That one is not needed. I will remove it.

> > 
> > User page tables was on the todo list, these are actually relatively
> > easy. The biggest issue is to detect them.
> > 
> > Metadata would likely need file system callbacks, which I would like to 
> > avoid at this point.
> 
> So I just don't know why you argue the point that you have lots
> of large holes left.

I didn't argue that. My point was just that I currently don't have
data what holes are the worst on given workloads. If I figure out at
some point that writeback pages are a significant part of some important
workload I would be interested in tackling them.
That said I think that's unlikely, but I'm not ruling it out.

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only.
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