Message-ID: <4761C8E4.2010900@rtr.ca>
Date: Thu, 13 Dec 2007 19:05:56 -0500
From: Mark Lord <liml@rtr.ca>
User-Agent: Thunderbird 2.0.0.9 (X11/20071031)
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To: Andrew Morton <akpm@linux-foundation.org>
Cc: James Bottomley <James.Bottomley@HansenPartnership.com>,
       jens.axboe@oracle.com, lkml@rtr.ca, matthew@wil.cx,
       linux-ide@vger.kernel.org, linux-kernel@vger.kernel.org,
       linux-scsi@vger.kernel.org, linux-mm@kvack.org, mel@csn.ul.ie
Subject: Re: QUEUE_FLAG_CLUSTER: not working in 2.6.24 ?
References: <20071213185326.GQ26334@parisc-linux.org>	<4761821F.3050602@rtr.ca>	<20071213192633.GD10104@kernel.dk>	<4761883A.7050908@rtr.ca>	<476188C4.9030802@rtr.ca>	<20071213193937.GG10104@kernel.dk>	<47618B0B.8020203@rtr.ca>	<20071213195350.GH10104@kernel.dk>	<20071213200219.GI10104@kernel.dk>	<476190BE.9010405@rtr.ca>	<20071213200958.GK10104@kernel.dk>	<20071213140207.111f94e2.akpm@linux-foundation.org>	<1197584106.3154.55.camel@localhost.localdomain> <20071213142935.47ff19d9.akpm@linux-foundation.org> <4761B32A.3070201@rtr.ca> <4761BCB4.1060601@rtr.ca>
In-Reply-To: <4761BCB4.1060601@rtr.ca>
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Mark Lord wrote:
> Mark Lord wrote:
>> Andrew Morton wrote:
>>> On Thu, 13 Dec 2007 17:15:06 -0500
>>> James Bottomley <James.Bottomley@HansenPartnership.com> wrote:
>>>
>>>> On Thu, 2007-12-13 at 14:02 -0800, Andrew Morton wrote:
>>>>> On Thu, 13 Dec 2007 21:09:59 +0100
>>>>> Jens Axboe <jens.axboe@oracle.com> wrote:
>>>>>
>>>>>> OK, it's a vm issue,
>>>>> cc linux-mm and probable culprit.
>>>>>
>>>>>>  I have tens of thousand "backward" pages after a
>>>>>> boot - IOW, bvec->bv_page is the page before bvprv->bv_page, not
>>>>>> reverse. So it looks like that bug got reintroduced.
>>>>> Bill Irwin fixed this a couple of years back: changed the page 
>>>>> allocator so
>>>>> that it mostly hands out pages in ascending physical-address order.
>>>>>
>>>>> I guess we broke that, quite possibly in Mel's page allocator rework.
>>>>>
>>>>> It would help if you could provide us with a simple recipe for
>>>>> demonstrating this problem, please.
>>>> The simple way seems to be to malloc a large area, touch every page and
>>>> then look at the physical pages assigned ... they now mostly seem to be
>>>> descending in physical address.
>>>>
>>>
>>> OIC.  -mm's /proc/pid/pagemap can be used to get the pfn's...
>> ..
>>
>> I'm actually running the treadmill right now (have been for many 
>> hours, actually,
>> to bisect it to a specific commit.
>>
>> Thought I was almost done, and then noticed that git-bisect doesn't keep
>> the Makefile VERSION lines the same, so I was actually running the wrong
>> kernel after the first few times.. duh.
>>
>> Wrote a script to fix it now.
> ..
> 
> Well, that was a waste of three hours.
..

Ahh.. it seems to be sensitive to one/both of these:

CONFIG_HIGHMEM64G=y with 4GB RAM:  not so bad, frequently does 20KB - 48KB segments.
CONFIG_HIGHMEM4G=y  with 2GB RAM:  very severe, rarely does more than 8KB segments.
CONFIG_HIGHMEM4G=y  with 3GB RAM:  very severe, rarely does more than 8KB segments.

So if you want to reproduce this on a large memory machine, use "mem=2GB" for starters.

Still testing..


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