Last modified: Sun Mar 29 12:53:57 EDT 2020
In the Linux kernel source tree, see Documentation/admin-guide/mm/hugetlbpage.rst and transhuge.rst.
If the flags in /proc/cpuinfo include pdpe1gb, your CPU supports 1 GiB pages. Compared with the 4 KiB and 2 MiB pages that the kernel normally doles out to applications, 1 GiB pages might offer a marginal performance boost. I find that they somehow make QEMU less crashy.
Since the kernel has no interest in using 1 GiB pages automatically, they must be allocated at boot time. This memory is subtracted from the common pool and unfortunately becomes unavailable for other uses.
To set aside 4 × 1 GiB hugepages, boot with kernel parameters
hugepagesz=1GB hugepages=4.
QEMU still cannot use these pages without a further step of mounting a pseudo-filesystem though which it can mmap them:
if [ -e /sys/kernel/mm/hugepages/hugepages-1048576kB/free_hugepages ]; then
NRP=`cat /sys/kernel/mm/hugepages/hugepages-1048576kB/free_hugepages`
if [ ${NRP} -gt 0 ]; then
echo "Mounting hugetlbfs with pagesize=1G,size=${NRP}G,min_size=${NRP}G."
if [ ! -d /hugepages ]; then
mkdir /hugepages
fi
mount -t hugetlbfs \
-o uid=1000,gid=100,pagesize=1G,size=${NRP}G,min_size=${NRP}G \
hugetlbfs /hugepages
else
echo "No free 1 GiB hugepages; not mounting hugetlbfs."
fi
else
echo "No 1 GiB hugepages; not mounting hugetlbfs."
fi
(Beware of the access granted to unprivileged users by
uid=1000,gid=100 and adjust as appropriate.)
QEMU can then be told to use those hugepages for guest memory with the
options -m 4G -mem-prealloc -mem-path /hugepages/qemu.