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

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Message-ID: <20090603102151.GM11363@kernel.dk>
Date:	Wed, 3 Jun 2009 12:21:51 +0200
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Wu Fengguang <fengguang.wu@...el.com>
Cc:	Nick Piggin <npiggin@...e.de>, Andi Kleen <andi@...stfloor.org>,
	"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, Wu Fengguang wrote:
> > And then this is possible because you aren't violating mm
> > assumptions due to 1b. This proceeds just as the existing
> > pagecache mce error handler case which exists now.
> 
> Yeah that's a good scheme - we are talking about two interception
> scheme. Mine is passive one and yours is active one.
> 
> passive: check hwpoison pages at __generic_make_request()/elv_next_request() 
>          (the code will be enabled by an mce_bad_io_pages counter)

That's not a feasible approach at all, it'll add O(N) scan of a bio at
queue time. Ditto for the elv_next_request() approach.

What would be cheaper is to check the pages at dma map time, since you
have to scan the request anyway. That means putting it in
blk_rq_map_sg() or similar.

-- 
Jens Axboe

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