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 <b...@decadent.org.uk> > --- > 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?
