linux-kernel - Re: [Xen-devel] [PATCH] xen: actually release memory when shrinking domain

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Date:	Fri, 23 Jan 2009 08:16:26 -0800
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Ian Campbell <Ian.Campbell@...rix.com>
CC:	Ingo Molnar <mingo@...e.hu>,
	"dan.magenheimer@...cle.com" <dan.magenheimer@...cle.com>,
	Xen-devel <xen-devel@...ts.xensource.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Stable Kernel <stable@...nel.org>
Subject: Re: [Xen-devel] [PATCH] xen: actually release memory when	shrinking
 domain

Ian Campbell wrote:
> On Thu, 2009-01-22 at 14:36 -0800, Jeremy Fitzhardinge wrote:
>   
>> From: Dan Magenheimer <dan.magenheimer@...cle.com>
>>
>> Fix this:
>>
>>     
>>> It appears that in the upstream balloon driver,
>>>       
>>>> the call to HYPERVISOR_update_va_mapping is missing
>>>> from decrease_reservation.  I think as a result,
>>>> the balloon driver is eating memory but not
>>>> releasing it to Xen, thus rendering the balloon
>>>> driver essentially useless.  (Can be observed via xentop.)
>>>>         
>
> Fails on 32 bit with HighMem pages:
>         
>         kernel BUG at /local/scratch/ianc/devel/kernels/paravirt/drivers/xen/balloon.c:298!
>   

Ah, good point.  Could you package this up into a proper patch for Ingo?

Thanks,
    J
>         invalid opcode: 0000 [#1] SMP 
>         last sysfs file: /sys/devices/system/xen_memory/xen_memory0/info/current_kb
>         Modules linked in:
>         
>         Pid: 9, comm: events/0 Tainted: G        W  (2.6.29-rc1-x86_32p-xen0-tip #726)         
>         EIP: 0061:[<c0266c57>] EFLAGS: 00010282 CPU: 0
>         EIP is at balloon_process+0x527/0x530
>         EAX: ffffffea EBX: deadbeef ECX: deadbeef EDX: deadbeef
>         ESI: deadbeef EDI: c1000000 EBP: 00000000 ESP: f64b5f44
>          DS: 007b ES: 007b FS: 00d8 GS: 0000 SS: 0069
>         Process events/0 (pid: 9, ti=f64b4000 task=f642d830 task.ti=f64b4000)
>         Stack:
>          00000000 ffffa0c0 0000002e 00000192 0000019d 00000000 00000400 f6427a00
>          00000000 00000000 00000000 00000000 00007ff0 c04afcb0 f6427a00 c04afcac
>          c0266730 c0143cf1 c0106bc2 f6427a0c c0107810 f642020c f6427a04 f6427a0c
>         Call Trace:
>          [<c0266730>] balloon_process+0x0/0x530
>          [<c0143cf1>] run_workqueue+0x91/0x140
>          [<c0106bc2>] check_events+0x8/0x16
>          [<c0107810>] xen_spin_unlock+0x0/0x50
>          [<c01473e0>] autoremove_wake_function+0x0/0x50
>          [<c0144718>] worker_thread+0x98/0xf0
>          [<c01473e0>] autoremove_wake_function+0x0/0x50
>          [<c0144680>] worker_thread+0x0/0xf0
>          [<c01470c2>] kthread+0x42/0x70
>          [<c0147080>] kthread+0x0/0x70
>          [<c010a5f3>] kernel_thread_helper+0x7/0x10
>         Code: 00 00 00 00 e8 9b a1 f0 ff 31 f6 e8 e4 2f eb ff b8 e0 7b 54 c0 e8 1a 90 16 00 8b 6c 24 18 89 44 24 14 89 74 24 10 e9 eb fe ff ff <0f> 0b eb fe 90 8d 74 26 00 83 ec 04 b8 20 fc 4a c0 e8 13 dc ff 
>         EIP: [<c0266c57>] balloon_process+0x527/0x530 SS:ESP 0069:f64b5f44
>         ---[ end trace 4eaa2a86a8e2da28 ]---
>
> diff -r b64a63f076cd drivers/xen/balloon.c
> --- a/drivers/xen/balloon.c	Fri Jan 23 13:29:48 2009 +0000
> +++ b/drivers/xen/balloon.c	Fri Jan 23 14:09:08 2009 +0000
> @@ -292,10 +292,13 @@
>  
>  		scrub_page(page);
>  
> -		ret = HYPERVISOR_update_va_mapping(
> -			(unsigned long)__va(pfn << PAGE_SHIFT),
> -			__pte_ma(0), 0);
> -		BUG_ON(ret);
> +		if (!PageHighMem(page)) {
> +			ret = HYPERVISOR_update_va_mapping(
> +				(unsigned long)__va(pfn << PAGE_SHIFT),
> +				__pte_ma(0), 0);
> +			BUG_ON(ret);
> +                }
> +
>  	}
>  
>  	/* Ensure that ballooned highmem pages don't have kmaps. */
>
>
>   

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