<div dir="ltr">I'm also interested in this. Running your 3 commands only gave me 3650 hugepages on a 32 GB system. I wonder if there is a way to have qemu use available hugepages first and then fall back on normal memory once depleted. </div><div class="gmail_extra"> <div class="gmail_quote">On Wed, Jul 6, 2016 at 2:48 PM, Thomas Lindroth <<a href="mailto:thomas.lindroth@gmail.com" target="_blank">thomas.lindroth@gmail.com</a>> wrote: <blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Hugetlbfs requires reservation of huge pages before files can be put on it. The easiest way of doing that is adding a hugepages argument to the kernel but that permanently reserves the pages and I don't want to waste 8G of ram all the time. Another way is to dynamically allocate them by echoing 4096 into /proc/sys/vm/nr_hugepages but if the computer has been running for more than an hour I'll be lucky to get 20 pages like that. The physical ram is too fragmented for dynamic allocation of huge pages but there is a workaround. The quickest way to defragment a hard drive is to delete all files and the fastest way to defragment ram is do drop caches. By running echo 3 > /proc/sys/vm/drop_caches before echo 4096 > /proc/sys/vm/nr_hugepages the allocation is much more likely to succeed but not guaranteed. Application memory could still be too fragmented. For that I would echo 1 > /proc/sys/vm/compact_memory which should compact all free space into continuous areas. I've never tried to compact memory because cache dropping is usually enough when using 2M huge pages. Is there no better way of doing this? The kernel could selectively drop cache pages to make huge pages without dropping all caches and if that is not enough it could compact only the memory needed. I've looked for an option like that but I've haven't found anything. The closest thing I've seen is echo "always" >/sys/kernel/mm/transparent_hugepage/defrag but that is only for transparent huge pages. _______________________________________________ vfio-users mailing list <a href="mailto:vfio-users@redhat.com">vfio-users@redhat.com</a> <a href="https://www.redhat.com/mailman/listinfo/vfio-users" rel="noreferrer" target="_blank">https://www.redhat.com/mailman/listinfo/vfio-users</a> </blockquote></div> </div>