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Re: [Xen-devel] [PATCH] xen: actually release memory when shrinking doma

To: Ian Campbell <Ian.Campbell@xxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH] xen: actually release memory when shrinking domain
From: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Date: Fri, 23 Jan 2009 08:16:26 -0800
Cc: Stable Kernel <stable@xxxxxxxxxx>, Ingo Molnar <mingo@xxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, "dan.magenheimer@xxxxxxxxxx" <dan.magenheimer@xxxxxxxxxx>, Linux Kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>
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Ian Campbell wrote:
On Thu, 2009-01-22 at 14:36 -0800, Jeremy Fitzhardinge wrote:
From: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>

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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