Tuesday, May 19, 2015

How to increase vmalloc size [vmalloc: allocation failure]


So this is what happened, I was working on the graphics driver and testing some GLBenchmark applications to see if everything is smooth and healthy. But one of the test was always failing for unknown reason (at that time). I have put more than couple of hours to debug that. I was ignoring some errors in dmesg (kernel log) that I was getting,

May 18 14:53:38 pc-vbox kernel: [412318.373157] vmap allocation for size 37752832 failed: use vmalloc=<size> to increase size.
May 18 14:53:38 pc-vbox kernel: [412318.373161] vmalloc: allocation failure: 37748736 bytes
May 18 14:53:38 pc-vbox kernel: [412318.373163] GLBenchmark27_X: page allocation failure: order:0, mode:0xd2

Latter I found that application was quite a heavy and vmalloc is failing due to insufficient space. On x86_32 systems default vmalloc size is 128MB and can be override by vmalloc kernel boot option. vmalloc() allocates block of memory with continuous virtual addresses or pages  (no guarantee that pages are actually contiguous in physical RAM) . You can find current vmalloc size of your system as bellow,

$cat /proc/meminfo | grep -i vmalloc

VmallocTotal: 122880 kB
VmallocUsed: 28216 kB
VmallocChunk: 94156 kB

How to increase vmalloc space?
We have to modify the kernel boot options in grub in order to do that.
open /etc/default/grub and make following change,
This will increase total vmalloc space to 512MB, next you need to update the grub as follows,

$sudo update-grub

After this corresponding  change will be reflected in /boot/grub/grub.cfg file as bellow,

Then just reboot the system and that solved my problem. Its not the thumb rule to set vmalloc to 512M but just set to what solves your problem!

After reboot you can see vmalloc size increased,

$cat /proc/meminfo | grep -i vmalloc
VmallocTotal:     524288 kB
VmallocUsed:       64768 kB
VmallocChunk:     366544 kB



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