linux-kernel - Re: [Linaro-mm-sig] [PATCH 04/11] mm: page_alloc: introduce alloc_contig

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Date:	Tue, 17 Jan 2012 16:46:37 -0800
From:	sandeep patil <psandeep.s@...il.com>
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,
	Daniel Walker <dwalker@...eaurora.org>,
	Russell King <linux@....linux.org.uk>,
	Arnd Bergmann <arnd@...db.de>,
	Jonathan Corbet <corbet@....net>, Mel Gorman <mel@....ul.ie>,
	Dave Hansen <dave@...ux.vnet.ibm.com>,
	Jesse Barker <jesse.barker@...aro.org>,
	Kyungmin Park <kyungmin.park@...sung.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: [Linaro-mm-sig] [PATCH 04/11] mm: page_alloc: introduce alloc_contig_range()

> Yeah, we are wondering ourselves about that.  Could you try cherry-picking
> commit ad10eb079c97e27b4d27bc755c605226ce1625de (update migrate type on pcp
> when isolating) from git://github.com/mina86/linux-2.6.git?  It probably
> won't
> apply cleanly but resolving the conflicts should not be hard (alternatively
> you can try branch cma from the same repo but it is a work in progress at
> the
> moment).
>

I'll try this patch and report back ,,


>> is set to MIGRATE_CMA instead of MIGRATE_ISOLATED.
>
>
> My understanding of that situation is that the page is on pcp list in which
> cases it's page_private is not updated.  Draining and the first patch in
> the series (and also the commit I've pointed to above) are designed to fix
> that but I'm unsure why they don't work all the time.
>
>

Will verify this if the page is found on the pcp list as well .

>> I've also had a test case where it failed because (page_count() != 0)

With this, when it failed the page_count()
returned a value of 2. I am not sure why, but I will try and see If I can
reproduce this.

>
>
>> Have you or anyone else seen this during the CMA testing?
>>
>> Also, could this be because we are finding a page within (start, end)
>> that actually belongs to a higher order Buddy block ?
>
>
> Higher order free buddy blocks are skipped in the “if (PageBuddy(page))”
> path of __test_page_isolated_in_pageblock().  Then again, now that I think
> of it, something fishy may be happening on the edges.  Moving the check
> outside of __alloc_contig_migrate_range() after outer_start is calculated
> in alloc_contig_range() could help.  I'll take a look at it.

I was going to suggest that, moving the check until after outer_start
is calculated
will definitely help IMO. I am sure I've seen a case where

  page_count(page) = page->private = 0 and PageBuddy(page) was false.

I will try and reproduce this as well.

Thanks,
Sandeep
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