Re: [Linaro-mm-sig] [PATCH 04/11] mm: page_alloc: introduce alloc_contig_range()

From: sandeep patil <psandeep.s@gmail.com>
To: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-media@vger.kernel.org, linux-mm@kvack.org,
	linaro-mm-sig@lists.linaro.org,
	Daniel Walker <dwalker@codeaurora.org>,
	Russell King <linux@arm.linux.org.uk>,
	Arnd Bergmann <arnd@arndb.de>, Jonathan Corbet <corbet@lwn.net>,
	Mel Gorman <mel@csn.ul.ie>, Michal Nazarewicz <mina86@mina86.com>,
	Dave Hansen <dave@linux.vnet.ibm.com>,
	Jesse Barker <jesse.barker@linaro.org>,
	Kyungmin Park <kyungmin.park@samsung.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Subject: Re: [Linaro-mm-sig] [PATCH 04/11] mm: page_alloc: introduce alloc_contig_range()
Date: Tue, 17 Jan 2012 13:54:28 -0800	[thread overview]
Message-ID: <CA+K6fF6A1kPUW-2Mw5+W_QaTuLfU0_m0aMYRLOg98mFKwZOhtQ@mail.gmail.com> (raw)
In-Reply-To: <1325162352-24709-5-git-send-email-m.szyprowski@samsung.com>

Marek,

I am running a CMA test where I keep allocating from a CMA region as long
as the allocation fails due to lack of space.

However, I am seeing failures much before I expect them to happen.
When the allocation fails, I see a warning coming from __alloc_contig_range(),
because test_pages_isolated() returned "true".

The new retry code does try a new range and eventually succeeds.

> +
> +static int __alloc_contig_migrate_range(unsigned long start, unsigned long end)
> +{
> +
> +done:
> +       /* Make sure all pages are isolated. */
> +       if (!ret) {
> +               lru_add_drain_all();
> +               drain_all_pages();
> +               if (WARN_ON(test_pages_isolated(start, end)))
> +                       ret = -EBUSY;
> +       }

I tried to find out why this happened and added in a debug print inside
__test_page_isolated_in_pageblock(). Here's the resulting log ..

---
[  133.563140] !!! Found unexpected page(pfn=9aaab), (count=0),
(isBuddy=no), (private=0x00000004), (flags=0x00000000), (_mapcount=0)
!!!
[  133.576690] ------------[ cut here ]------------
[  133.582489] WARNING: at mm/page_alloc.c:5804 alloc_contig_range+0x1a4/0x2c4()
[  133.594757] [<c003e814>] (unwind_backtrace+0x0/0xf0) from
[<c0079c7c>] (warn_slowpath_common+0x4c/0x64)
[  133.605468] [<c0079c7c>] (warn_slowpath_common+0x4c/0x64) from
[<c0079cac>] (warn_slowpath_null+0x18/0x1c)
[  133.616424] [<c0079cac>] (warn_slowpath_null+0x18/0x1c) from
[<c00e0e84>] (alloc_contig_range+0x1a4/0x2c4)
[  133.627471] EXT4-fs (mmcblk0p25): re-mounted. Opts: (null)
[  133.633728] [<c00e0e84>] (alloc_contig_range+0x1a4/0x2c4) from
[<c0266690>] (dma_alloc_from_contiguous+0x114/0x1c8)
[  133.697113] !!! Found unexpected page(pfn=9aaac), (count=0),
(isBuddy=no), (private=0x00000004), (flags=0x00000000), (_mapcount=0)
!!!
[  133.710510] EXT4-fs (mmcblk0p26): re-mounted. Opts: (null)
[  133.716766] ------------[ cut here ]------------
[  133.721954] WARNING: at mm/page_alloc.c:5804 alloc_contig_range+0x1a4/0x2c4()
[  133.734100] Emergency Remount complete
[  133.742584] [<c003e814>] (unwind_backtrace+0x0/0xf0) from
[<c0079c7c>] (warn_slowpath_common+0x4c/0x64)
[  133.753448] [<c0079c7c>] (warn_slowpath_common+0x4c/0x64) from
[<c0079cac>] (warn_slowpath_null+0x18/0x1c)
[  133.764373] [<c0079cac>] (warn_slowpath_null+0x18/0x1c) from
[<c00e0e84>] (alloc_contig_range+0x1a4/0x2c4)
[  133.775299] [<c00e0e84>] (alloc_contig_range+0x1a4/0x2c4) from
[<c0266690>] (dma_alloc_from_contiguous+0x114/0x1c8)
---

>From the log it looks like the warning showed up because page->private
is set to MIGRATE_CMA instead of MIGRATE_ISOLATED.
I've also had a test case where it failed because (page_count() != 0)

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 ?

Thanks,
Sandeep