On Tue, 2015-11-10 at 12:01 -0800, David Rientjes wrote: > On Sat, 31 Oct 2015, Ben Hutchings wrote: > > > If we need to increase the number of huge pages, drop caches first > > to reduce fragmentation and then check that we actually allocated > > as many as we wanted. Retry once if that doesn't work. > > > > Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx> > > --- > > The test always fails for me in a 1 GB VM without this. > > > > Ben. > > > > tools/testing/selftests/vm/run_vmtests | 15 ++++++++++++++- > > 1 file changed, 14 insertions(+), 1 deletion(-) > > > > diff --git a/tools/testing/selftests/vm/run_vmtests b/tools/testing/selftests/vm/run_vmtests > > index 9179ce8..97ed1b2 100755 > > --- a/tools/testing/selftests/vm/run_vmtests > > +++ b/tools/testing/selftests/vm/run_vmtests > > @@ -20,13 +20,26 @@ done < /proc/meminfo > > if [ -n "$freepgs" ] && [ -n "$pgsize" ]; then > > nr_hugepgs=`cat /proc/sys/vm/nr_hugepages` > > needpgs=`expr $needmem / $pgsize` > > - if [ $freepgs -lt $needpgs ]; then > > + tries=2 > > + while [ $tries -gt 0 ] && [ $freepgs -lt $needpgs ]; do > > lackpgs=$(( $needpgs - $freepgs )) > > + echo 3 > /proc/sys/vm/drop_caches > > echo $(( $lackpgs + $nr_hugepgs )) > /proc/sys/vm/nr_hugepages > > if [ $? -ne 0 ]; then > > echo "Please run this test as root" > > exit 1 > > fi > > + while read name size unit; do > > + if [ "$name" = "HugePages_Free:" ]; then > > + freepgs=$size > > + fi > > + done < /proc/meminfo > > + tries=$((tries - 1)) > > + done > > + if [ $freepgs -lt $needpgs ]; then > > + printf "Not enough huge pages available (%d < %d)\n" \ > > + $freepgs $needpgs > > + exit 1 > > fi > > else > > echo "no hugetlbfs support in kernel?" > > > > I know this patch is in -mm and hasn't been merged by Linus yet, but I'm > wondering why the multiple /proc/sys/vm/drop_caches is helping? Would it > simply suffice to put a sleep in there instead or is drop_caches actually > doing something useful a second time around? Initially I just retried setting nr_hugepages up to 10 times, which wasn't sufficient. Then I added the drop_caches, and after that setting nr_hugepages tended to worked first time so I reduced the retry count. It might not be necessary to retry at all. Ben. -- Ben Hutchings All the simple programs have been written, and all the good names taken.
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