linux-kernel - Re: [PATCH 2/9] mm: alloc_contig_freed

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Message-ID: <20111101150448.GD14998@csn.ul.ie>
Date:	Tue, 1 Nov 2011 15:04:48 +0000
From:	Mel Gorman <mel@....ul.ie>
To:	Michal Nazarewicz <mina86@...a86.com>
Cc:	Marek Szyprowski <m.szyprowski@...sung.com>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-media@...r.kernel.org, linux-mm@...ck.org,
	linaro-mm-sig@...ts.linaro.org,
	Kyungmin Park <kyungmin.park@...sung.com>,
	Russell King <linux@....linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Ankita Garg <ankita@...ibm.com>,
	Daniel Walker <dwalker@...eaurora.org>,
	Arnd Bergmann <arnd@...db.de>,
	Jesse Barker <jesse.barker@...aro.org>,
	Jonathan Corbet <corbet@....net>,
	Shariq Hasnain <shariq.hasnain@...aro.org>,
	Chunsang Jeong <chunsang.jeong@...aro.org>,
	Dave Hansen <dave@...ux.vnet.ibm.com>
Subject: Re: [PATCH 2/9] mm: alloc_contig_freed_pages() added

On Sun, Oct 23, 2011 at 09:05:05PM -0700, Michal Nazarewicz wrote:
> > On Thu, Oct 06, 2011 at 03:54:42PM +0200, Marek Szyprowski wrote:
> >> This commit introduces alloc_contig_freed_pages() function
> >> which allocates (ie. removes from buddy system) free pages
> >> in range. Caller has to guarantee that all pages in range
> >> are in buddy system.
> 
> On Tue, 18 Oct 2011 05:21:09 -0700, Mel Gorman <mel@....ul.ie> wrote:
> > Straight away, I'm wondering why you didn't use
> > mm/compaction.c#isolate_freepages()
> 
> Does the below look like a step in the right direction?
> 
> It basically moves isolate_freepages_block() to page_alloc.c (changing

For the purposes of review, have a separate patch for moving
isolate_freepages_block to another file that does not alter the
function in any way. When the function is updated in a follow-on patch,
it'll be far easier to see what has changed.

page_isolation.c may also be a better fit than page_alloc.c

As it is, the patch for isolate_freepages_block is almost impossible
to read because it's getting munged with existing code that is already
in page_alloc.c . About all I caught from it is that scannedp does
not have a type. It defaults to unsigned int but it's unnecessarily
obscure.

> it name to isolate_freepages_range()) and changes it so that depending
> on arguments it treats holes (either invalid PFN or non-free page) as
> errors so that CMA can use it.
> 

I haven't actually read the function because it's too badly mixed with
page_alloc.c code but this description fits what I'm looking for.

> It also accepts a range rather then just assuming a single pageblock
> thus the change moves range calculation in compaction.c from
> isolate_freepages_block() up to isolate_freepages().
> 
> The change also modifies spilt_free_page() so that it does not try to
> change pageblock's migrate type if current migrate type is ISOLATE or
> CMA.
> 

This is fine. Later, the flags that determine what happens to pageblocks
may be placed in compact_control.

> ---
>  include/linux/mm.h             |    1 -
>  include/linux/page-isolation.h |    4 +-
>  mm/compaction.c                |   73 +++--------------------
>  mm/internal.h                  |    5 ++
>  mm/page_alloc.c                |  128 +++++++++++++++++++++++++---------------
>  5 files changed, 95 insertions(+), 116 deletions(-)
> 

I confess I didn't read closely because of the mess in page_alloc.c but
the intent seems fine. Hopefully there will be a new version of CMA
posted that will be easier to review.

Thanks

-- 
Mel Gorman
SUSE Labs
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