[LU-18147] client page cache - page still in cache

• Type: Bug
• Resolution: Unresolved
• Priority: Blocker
• Affects Version/s: Lustre 2.16.0
• Environment: 018c4e8f25 (origin/master, origin/HEAD) LU-18110 doc: lctl multiple NIDs specification not clear
• Severity: 3
• Assignee: Patrick Farrell (Inactive)
• Reporter: Alexey Lyashkov

Description

While creating a test case for RA bug I started to write a test script and found anomaly in the client side.
test scripts is

test_117() {
        local stripe_size
        (( $OSTCOUNT >= 2 )) || skip "needs >= 2 OSTs"
        $LCTL set_param llite.*.hybrid_io=0
        rm -rf $DIR/$tdir
        mkdir -p $DIR/$tdir
        $LFS setstripe -c 2 -S 1M $DIR/$tdir/$tfile || error "can't set striping"
        stripe_size=$($LFS getstripe -S $DIR/$tdir/$tfile)
        $LCTL mark "==== write"
        dd if=/dev/zero of=$DIR/$tdir/$tfile bs=$stripe_size count=10 oflag=sync
        sync
        $LCTL mark "=== read"
        for i in /sys/devices/virtual/bdi/lustre-*; do
        echo 2048 > $i/read_ahead_kb
        done
dir=/sys/kernel/debug/tracing
set -x
pushd $dir
sysctl kernel.ftrace_enabled=1
echo 0 > tracing_on
echo 10000 > buffer_size_kb
#echo 'nop' > current_tracer
#echo '' >set_graph_function
echo function_graph > current_tracer
echo vfs_fadvise > set_graph_function
echo > kprobe_events
echo 'p:kp1 __do_page_cache_readahead %di +80(+0(%di)):u64 %dx %cx' > kprobe_events
echo 'r:kp2 __do_page_cache_readahead $retval' >> kprobe_events
echo 'p:kp3 __do_page_cache_readahead+100 %ax %cx %dx %di' >> kprobe_events
# ax - page
# r13 - nr_read
echo 'p:kp4 __do_page_cache_readahead+309 %ax %r13' >> kprobe_events
echo 1 > events/kprobes/kp1/enable
echo 1 > events/kprobes/kp2/enable
echo 1 > events/kprobes/kp3/enable
echo 1 > events/kprobes/kp4/enable
echo > trace
echo 1 > tracing_on
popd
        fadvise_dontneed_helper $DIR/$tdir/$tfile
        fadvise_willneed_helper $DIR/$tdir/$tfile 0 $((stripe_size * 4 ))
pushd $dir
echo 0 > events/kprobes/kp1/enable
echo 0 > events/kprobes/kp2/enable
echo 0 > events/kprobes/kp3/enable
echo 0 > events/kprobes/kp4/enable
echo 0 > tracing_on
cat trace > /tmp/trace
echo > trace
echo > kprobe_events
popd
set +x
}
run_test 117 "RA should don't panic for multistripe"

fadvise_willneed_helper - just issue an advice(WILLNEED) or same readahead(2) may used.
and it don't work. While inspecting a source this bug I started to trace client side and found
fadvice found a page in the page cache, while dontneed_helper invalidate a pages in cache.

ftrace log don't have a readpage calls which expected as pages removed from page cache.
I tries with sysctl -w vm.drop_caches=1 and it have same result - page live in page cache and have uptodate flags.

Switching to the cray 2.15 code I don't see this bug and ftrace log have a records about readpage calls.