linux-kernel - Re: [PATCH] [11/16] HWPOISON: check and isolate corrupted free pages v2

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Date:	Tue, 9 Jun 2009 15:55:14 +0200
From:	Nick Piggin <npiggin@...e.de>
To:	Wu Fengguang <fengguang.wu@...el.com>
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>
Subject: Re: [PATCH] [11/16] HWPOISON: check and isolate corrupted free pages v2

On Tue, Jun 09, 2009 at 09:49:03PM +0800, Wu Fengguang wrote:
> On Tue, Jun 09, 2009 at 09:28:47PM +0800, Nick Piggin wrote:
> > And I don't think removing a free page from the page allocator is
> > too much more complex than removing a live page from the pagecache ;)
> 
> There are usable functions for doing pagecache isolations, but no one
> to isolate one specific page from the buddy system.

But it shouldn't be too hard. Anyway you wanted to reinvent your
own functions for pagecache isolations ;)

> Plus, if we did present such a function, you'll then ask for it being
> included in page_alloc.c, injecting a big chunk of dead code into the
> really hot code blocks and possibly polluting the L2 cache. Will it be

But you would say no because you like it better in your memory
isolation file ;)

> better than just inserting several lines? Hardly. Smaller text itself
> yields faster speed.

Oh speed I'm definitely thinking about, don't worry about that.

Moving hot and cold functions together could become an issue
indeed. Mostly it probably matters a little less than code
within a single function due to their size. But I think gcc
already has options to annotate this kind of thing which we
could be using.

So it's not such a good argument against moving things out of
hotpaths, or guiding in which files to place functions.

Anyway, in this case it is not a "nack" from me. Just that I
would like to see the non-fastpath code too or at least if
it can be thought about.

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