mjhjmtu

I have reserved hugepages for my process using below commands:

#echo 64 > /sys/kernel/mm/hugepages/hugepages-2048kB/nr_hugepages
#mkdir -p /mnt/huge && mount -t hugetlbfs nodev /mnt/huge .

And I have placed it in rc.local file.

After machine reboot, huge pages reserved successfully and /mnt/huge created.

But before my process startups, I could see 21 hugepages are not available for reservation.
Below command output:

# cat /proc/meminfo | grep Huge 
HugePages_Total: 64 
HugePages_Free: 43 
HugePages_Rsvd: 43 
HugePages_Surp: 0 
Hugepagesize: 2048 kB 

And no results for the below commands:

# lsof |grep /mnt/huge 
[root@CLA-0(11) /root] 

Then I tried to free hugepages ...

# echo 0 > /sys/kernel/mm/hugepages/hugepages-2048kB/nr_hugepages 

No error message displayed. But below command output tells no change ..

# cat /sys/kernel/mm/hugepages/hugepages-2048kB/nr_hugepages 
 0 

But I could see if we echo > 64 it updates nr_hugepages. Also tested with other numbers, it only updates if value is greater then current value in nr_hugepages.

I am looking for below clarification in this site:

1. 43 hugepages are free , who requested 21 hugepages allocation out of 64.


2. Why echo 0 > /sys/kernel/mm/hugepages/hugepages-2048kB/nr_hugepage is not updating nr_hugepages

Linux Kernel

# cat /proc/version 
Linux version 2.6.34.13-WR4.3.x86_64_fbsa_standard-00038-gc4b8cb8 (gcc version 4.4.1 (Wind River Linux Sourcery G++ 4.4a-431) ) #1 SMP Wed Jan 8 20:40:41 EET 2014

I haven't found a perfect answer to this problem but you can obtain usable space using the following

#!/bin/sh
# 
echo "Re-establishing and defragmenting hugepages "
sysctl -p
hugeadm --pool-pages-min=DEFAULT:+[page-count] –add-temp-swap=400
echo “ “
echo “Updated hugepages “
cat /proc/meminfo |grep HugePage

This will consolidate the reserved pages into one place using a swap file of 400 pages (in this case) and attempt to ensure / append the required number available pages specified in [page-count]. The script assumes you have defined the desired number of initial pages in /etc/sysctl.conf
More information in the manual entry for hugeadm