linux-kernel - Re: [PATCH] [11/19] HWPOISON: Refactor truncate to allow direct truncating of page v2

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Date:	Wed, 5 Aug 2009 23:12:20 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	Nick Piggin <npiggin@...e.de>
Cc:	Andi Kleen <andi@...stfloor.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"hidehiro.kawai.ez@...achi.com" <hidehiro.kawai.ez@...achi.com>
Subject: Re: [PATCH] [11/19] HWPOISON: Refactor truncate to allow direct
	truncating of page v2

On Wed, Aug 05, 2009 at 10:01:45PM +0800, Nick Piggin wrote:
> On Wed, Aug 05, 2009 at 03:46:08PM +0200, Andi Kleen wrote:
> > On Wed, Aug 05, 2009 at 12:20:08PM +0200, Nick Piggin wrote:
> > > >  truncate_complete_page(struct address_space *mapping, struct page *page)
> > > >  {
> > > >  	if (page->mapping != mapping)
> > > > -		return;
> > > > +		return -EIO;
> > > 
> > > Hmm, at this point, the page must have been removed from pagecache,
> > > so I don't know if you need to pass an error back?
> > 
> > It could be reused, which would be bad for us?
>  
> I haven't brought up the caller at this point, but IIRC you had
> the page locked and mapping confirmed at this point anyway so
> it would never be an error for your code.

Right, that 'if' will always evaluate to false for the hwpoison case.
Because that 'mapping' was taken from 'page->mapping' inside page lock
and they will just remain the same values.

> Probably it would be nice to just force callers to verify the page.
> Normally IMO it is much nicer and clearer to do it at the time the
> page gets locked, unless there is good reason otherwise.

Yes we do checked page->mapping after taking page lock.
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