| Hello.
we have experience this problem many time, and we try many ways to solve this problem, but always failed.
such as sync && echo 3 > /proc/sys/vm/drop_caches to free more memory, however, after a while, the message come again.
the dmesg show: May 30 12:35:51 w-openstack21 kernel: XFS: possible memory allocation deadlock in kmem_alloc (mode:0x250) May 30 12:35:53 w-openstack21 kernel: XFS: possible memory allocation deadlock in kmem_alloc (mode:0x250) May 30 12:35:55 w-openstack21 kernel: XFS: possible memory allocation deadlock in kmem_alloc (mode:0x250) May 30 12:35:57 w-openstack21 kernel: XFS: possible memory allocation deadlock in kmem_alloc (mode:0x250) May 30 12:35:59 w-openstack21 kernel: XFS: possible memory allocation deadlock in kmem_alloc (mode:0x250)
our kernel version is 3.10.0-327.4.5.el7.x86_64
we think this is the kernel memory fragmentation problem, when dmesg show the error message, we check the buddyinfo
[root@w-openstack21 /home/xusiliang]# cat /proc/buddyinfo Node 0, zone DMA 1 0 1 0 2 1 1 0 1 1 3 Node 0, zone DMA32 2190 1898 1367 583 284 81 21 8 5 0 4 Node 0, zone Normal 85195 90572 56688 32379 16793 5568 930 230 184 11 0 Node 1, zone Normal 95799 127034 94363 49321 21555 5239 225 2 2 0 0
and I think the kernel have enough free memory [root@w-openstack21 /home/xusiliang]# free -m total used free shared buff/cache available Mem: 64269 50357 11802 65 2109 11757 Swap: 32255 347 31908
This machine is running for qemu, the file is qemu qcow file type
[root@w-openstack20 /data/nova/instances/7898b630-c4ef-49ab-9ce9-3735e090c282]# file disk disk: QEMU QCOW Image (v3), has backing file (path /data/nova/instances/_base/3f27393376152ac352b2d85703011e38517e), 429496729600 bytes
we also use xfs_db to check the fragmentation
[root@w-openstack20 /home/xusiliang]# xfs_db -r /dev/mapper/VolGroup00-LogVol04 xfs_db> frag
actual 48421430, ideal 20716, fragmentation factor 99.96%
How can I solve this problem, what do you suggest me to do?
thank you
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