How to use, monitor, and disable transparent hugepages in Red Hat Enterprise Linux ?

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Solution Verified - Updated July 8 2025 at 12:52 AM - English Environment Red Hat Enterprise Linux 10 Red Hat Enterprise Linux 9 Red Hat Enterprise Linux 8 Red Hat Enterprise Linux 7 Red Hat Enterprise Linux 6 transparent hugepages (THP) Issue How do transparent hugepages work in RHEL 6? How are transparent hugepages activated by a process? Do we still need to preallocate some amount of memory for use as (transparent) hugepages? How can I see the number of transparent hugepages that are actually in use on the system (either globally or by individual processes)? How do I enable HugePages on Red Hat Enterprise Linux? How do I disable HugePages on Red Hat Enterprise Linux? Freezing issue while streaming out from RHEL 6.2 server, We are providing a streaming platform (RTSP, HLS) to our customers, based on RHEL 6.2 x86_64 While streaming out, we experiencing delays (more than one to ten seconds) because of a process freeze and at the same point in time a bunch of memory is being freed Need assistance to Disable Transparent Huge Pages (THP) in RHEL 7.4 Resolution Note: Transparent Huge Pages are not available on the 32-bit version of RHEL 6. For RHEL 7 and above see How to disable transparent hugepages (THP) on Red Hat Enterprise Linux ?

Transparent Huge Pages (THP) are enabled by default in RHEL 6 for all applications. The kernel attempts to allocate hugepages whenever possible and any Linux process will receive 2MB pages if the mmap region is 2MB naturally aligned. The main kernel address space itself is mapped with hugepages, reducing TLB pressure from kernel code. For general information on Hugepages, see: What are Huge Pages and what are the advantages of using them?

The kernel will always attempt to satisfy a memory allocation using hugepages. If no hugepages are available (due to non availability of physically continuous memory for example) the kernel will fall back to the regular 4KB pages. THP are also swappable (unlike hugetlbfs). This is achieved by breaking the huge page to smaller 4KB pages, which are then swapped out normally.

But to use hugepages effectively, the kernel must find physically continuous areas of memory big enough to satisfy the request, and also properly aligned. For this, a khugepaged kernel thread has been added. This thread will occasionally attempt to substitute smaller pages being used currently with a hugepage allocation, thus maximising THP usage.

In userland, no modifications to the applications are necessary (hence transparent). But there are ways to optimise its use. For applications that want to use hugepages, use of posix_memalign() can also help ensure that large allocations are aligned to huge page (2MB) boundaries.

Also, THP is only enabled for anonymous memory regions. There are plans to add support for tmpfs and page cache. THP tunables are found in the /sys tree under /sys/kernel/mm/transparent_hugepage in RHEL 7 and later RHEL 6 releases. The directory for earlier RHEL 6 releases is /sys/kernel/mm/redhat_transparent_hugepage. The first location will be used further in this document.

The values for /sys/kernel/mm/transparent_hugepage/enabled can be one of the following:

Raw always - always use THP never - disable THP khugepaged will be automatically started when transparent_hugepage/enabled is set to “always” or “madvise”, and it’ll be automatically shutdown if it’s set to “never”. The transparent_hugepage/defrag parameter takes the same values and it controls whether the kernel should make aggressive use of memory compaction to make more hugepages available.

Check system-wide THP usage Run the following command to check system-wide THP usage:

Raw

grep AnonHugePages /proc/meminfo

AnonHugePages: 632832 kB Note: Red Hat Enterprise Linux 6.2 or later publishes additional THP monitoring via /proc/vmstat:

Raw

egrep ‘trans|thp’ /proc/vmstat

nr_anon_transparent_hugepages 2018 thp_fault_alloc 7302 thp_fault_fallback 0 thp_collapse_alloc 401 thp_collapse_alloc_failed 0 thp_split 21 Raw thp_fault_alloc: is incremented every time a huge page is successfully allocated to handle a page fault.

thp_collapse_alloc: is incremented by khugepaged when it has found a range of pages to collapse into one huge page and has successfully allocated a new huge page to store the data.

thp_fault_fallback: is incremented if a page fault fails to allocate a huge page and instead falls back to using small pages.

thp_collapse_alloc_failed: is incremented if khugepaged found a range of pages that should be collapsed into one huge page but failed the allocation.

thp_split_page: is incremented every time a huge page is split into base pages. This can happen for a variety of reasons but a common reason is that a huge page is old and is being reclaimed.

thp_zero_page_alloc: is incremented every time a huge zero page is successfully allocated. It includes allocations which where dropped due race with other allocation. Note, it doesn’t count every map of the huge zero page, only its allocation.

thp_zero_page_alloc_failed: is incremented if kernel fails to allocate huge zero page and falls back to using small pages.

Check THP usage per process Run the following command to check which processes are using THP:

Raw # awk ‘/AnonHugePages/ { if($2>4){print FILENAME “ “ $0; system(“ps -fp “ gensub(/.\/([0-9]+)./, “\1”, “g”, FILENAME))}}’ /proc/*/smaps /proc/7519/smaps:AnonHugePages: 305152 kB UID PID PPID C STIME TTY TIME CMD qemu 7519 1 1 08:53 ? 00:00:48 /usr/bin/qemu-system-x86_64 -machine accel=kvm -name rhel7 -S -machine pc-i440fx-1.6,accel=kvm,usb=of /proc/7610/smaps:AnonHugePages: 491520 kB UID PID PPID C STIME TTY TIME CMD qemu 7610 1 2 08:53 ? 00:01:30 /usr/bin/qemu-system-x86_64 -machine accel=kvm -name util6vm -S -machine pc-i440fx-1.6,accel=kvm,usb= /proc/7788/smaps:AnonHugePages: 389120 kB UID PID PPID C STIME TTY TIME CMD qemu 7788 1 1 08:54 ? 00:00:55 /usr/bin/qemu-system-x86_64 -machine accel=kvm -name rhel64eus -S -machine pc-i440fx-1.6,accel=kvm,us

To disable THP at boot time Append the following to the kernel command line in grub.conf:

Raw transparent_hugepage=never Note: Certain ktune and/or tuned profiles specify to enable THP when they are applied. If the transparent_hugepage=never parameter is set at boot time, but THP does not appear to be disabled after the system is fully booted. Refer to the following article:

Disabling transparent hugepages (THP) on Red Hat Enterprise Linux 6 is not taking effect

Disable Transparent Huge Pages(THP) persistently not working on RHEL7

To disable THP at run time Run the following commands to disable THP on-the-fly:

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echo never > /sys/kernel/mm/transparent_hugepage/enabled

echo never > /sys/kernel/mm/transparent_hugepage/defrag

NOTE: Running the above commands will stop only creation and usage of the new THP. The THP which were created and used at the moment the above commands were run would not be disassembled into the regular memory pages. To get rid of THP completely the system should be rebooted with THP disabled at boot time. NOTE: Some third party application install scripts check value of above files and complain even if THP is disabled at boot time using transparent_hugepage=never, this is due to the fact when THP is disabled at boot time, the value of /sys/kernel/mm/transparent_hugepage/defrag will not be changed, however this is expected and system will never go in THP defragmentation code path when it is disabled at boot and THP defrag need not to be disabled separately.

How to tell if Explicit HugePages is enabled or disabled There can be two types of HugePages in the system: Explicit Huge Pages which are allocated explicitly by vm.nr_hugepages sysctl parameter and Transparent Huge Pages which are allocated automatically by the kernel. See below on how to tell if Explicit HugePages is enabled or disabled.

Explicit HugePages DISABLED:

If the value of HugePages_Total is “0” it means HugePages is disabled on the system.

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grep -i HugePages_Total /proc/meminfo

HugePages_Total: 0 Similarly, if the value in /proc/sys/vm/nr_hugepages file or vm.nr_hugepages sysctl parameter is “0” it means HugePages is disabled on the system:

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cat /proc/sys/vm/nr_hugepages

sysctl vm.nr_hugepages

vm.nr_hugepages = 0 Explicit HugePages ENABLED:

If the value of HugePages_Total is greater than “0”, it means HugePages is enabled on the system:

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grep -i HugePages_Total /proc/meminfo

HugePages_Total: 1024 Similarly if the value in /proc/sys/vm/nr_hugepages file or vm.nr_hugepages sysctl parameter is greater than “0”, it means HugePages is enabled on the system:

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cat /proc/sys/vm/nr_hugepages

1024

sysctl vm.nr_hugepages

vm.nr_hugepages = 1024

Comments RHEL 6 disables THP on systems with < 1G of ram. Refer to Red Hat Bug 618444 - disable transparent hugepages by default on small systems for more information. Disadvantages of using the explicit hugepages (libhugetlbfs): Using hugetlbfs requires significant work from both application developers and system administrators; explicit hugepages must be set aside at boot time, and applications must map them explicitly. The process is fiddly enough that use of hugetlbfs is restricted to those who really care and who have the time to mess with it. Hugetlbfs is often seen as a feature for large, proprietary database management systems and little else. Diagnostic Steps Links contained herein to external website(s) are provided for convenience only. Red Hat has not reviewed the links and is not responsible for the content or its availability. The inclusion of any link to an external website does not imply endorsement by Red Hat of the website or their entities, products or services. You agree that Red Hat is not responsible or liable for any loss or expenses that may result due to your use of (or reliance on) the external site or content.

References:

Transparent huge pages in 2.6.38 Documentation/vm/transhuge.txt Andrea Arcangeli’s presentation “Transparent Hugepage Support” : KVM Forum 2010 - Presentations How to disable transparent hugepages (THP) on Red Hat Enterprise Linux ? Product(s) Red Hat Enterprise LinuxComponent kernel kvmCategory Learn moreTags memory performance rhel_10 rhel_6 rhel_7 rhel_8 rhel_9 This solution is part of Red Hat’s fast-track publication program, providing a huge library of solutions that Red Hat engineers have created while supporting our customers. To give you the knowledge you need the instant it becomes available, these articles may be presented in a raw and unedited form.

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Community Member 37 points May 13, 2015 4:50 AM Not provided says: For RHEL 7

Add the following to the GRUB_CMDLINE_LINUX= line in /etc/sysconfig/grub:

transparent_hugepage=never Then rebuild grub:

grub2-mkconfig -o /boot/grub2/grub.cfg

Finally, disable tuned or it will turn THP back on:

systemctl disable tuned

Red Hat Pro 673 points May 13, 2015 5:05 AM Jeremy Eder says: Hi Kevin, we have a fix for tuned overridding kernel cmdline options queued up for RHEL7.2. The BZ number is https://bugzilla.redhat.com/show_bug.cgi?id=1189868

Reply Red Hat Newbie 10 points Jan 16, 2016 3:23 AM Martes says: Greetings Kevin, and Jeremy.

I have seen this topic referenced online, however, I believe the simplest method is to use “grubby” which updates grub.cfg.

I have been using the following, to update all kernel options at one time.

grubby –update-kernel=ALL –args=”transparent_hugepage=never”

However, I am still testing to see if it will persist across a kernel update, as would be the case when updating the GRB_CMDLINE_LINUX within /etc/default/grub file.

Reply Red Hat Guru 2828 points Oct 30, 2017 8:06 PM Oscar Arribas Arribas says: Take a look to How to disable transparent hugepages (THP) on Red Hat Enterprise Linux 7

Reply Active Contrib… 176 points Aug 5, 2020 9:23 AM Hamid Khan says: or you can create a file in /etc/tuned and place it there and restart tuned

Reply Community Member 68 points Oct 2, 2015 11:59 PM ICPSR Admin says: One other possible use of explicit hugepages is with Java. Oracle/openjdk accepts the command line argument -XX:+UseLargePages and will use hugepages for most of its memory pools if it’s enabled.

Guru 1512 points Aug 24, 2021 3:32 PM Sadashiva Murthy M says: RHCOE This should be correct. This is not the right path: “/sys/kernel/mm/redhat_transparent_hugepage/”. It should be “/sys/kernel/mm/transparent_hugepage/”. Please correct this.

Reply Red Hat Active Contrib… 270 points Aug 25, 2021 12:53 AM Vladislav Dronov says: This is a little bit more complicated. The path is without “redhat_” part in RHEL 7 and later RHEL 6 releases, but with “redhat_” part in earlier RHEL 6 releases. I’ve made the adjustment, thank you for noticing this.

Reply Newbie 14 points Sep 20, 2024 5:15 AM Joe Galluzzo says: Are there any differences from this doc for RHEL9?

Reply Pro 417 points Apr 11, 2025 4:57 PM Sophie l says: RHEL9: /sys/kernel/mm/transparent_hugepage/defrag is set to [madvise] by default even when hugepages is disabled in grub.