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selftests/ublk: add hugetlbfs shmem_zc test for loop target

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Add test_shmem_zc_02.sh which tests the UBLK_IO_F_SHMEM_ZC zero-copy
path on the loop target using a hugetlbfs shared buffer. Both kublk and
fio mmap the same hugetlbfs file with MAP_SHARED, sharing physical
pages. The kernel's PFN matching enables zero-copy — the loop target
reads/writes directly from the shared buffer to the backing file.

Uses standard fio --mem=mmaphuge:<path> (supported since fio 1.10),
no patched fio required.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://patch.msgid.link/20260331153207.3635125-9-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Ming Lei 2026-03-31 23:31:59 +08:00 committed by Jens Axboe
parent 2f1e9468bd
commit d486650332
2 changed files with 69 additions and 0 deletions
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1
tools/testing/selftests/ublk/Makefile
View File

@ -53,6 +53,7 @@ TEST_PROGS += test_part_01.sh
TEST_PROGS += test_part_02.sh
TEST_PROGS += test_shmemzc_01.sh
TEST_PROGS += test_shmemzc_02.sh
TEST_PROGS += test_stress_01.sh
TEST_PROGS += test_stress_02.sh

68
tools/testing/selftests/ublk/test_shmemzc_02.sh Executable file
View File

@ -0,0 +1,68 @@
#!/bin/bash
# SPDX-License-Identifier: GPL-2.0
# Test: shmem_zc with hugetlbfs buffer on loop target
#
# kublk and fio both mmap the same hugetlbfs file (MAP_SHARED),
# so they share physical pages. The kernel PFN match enables
# zero-copy I/O without socket-based fd passing.
. "$(cd "$(dirname "$0")" && pwd)"/test_common.sh
ERR_CODE=0
_prep_test "shmem_zc" "loop target hugetlbfs shmem zero-copy test"
if ! _have_program fio; then
echo "SKIP: fio not available"
exit "$UBLK_SKIP_CODE"
fi
if ! grep -q hugetlbfs /proc/filesystems; then
echo "SKIP: hugetlbfs not supported"
exit "$UBLK_SKIP_CODE"
fi
# Allocate hugepages
OLD_NR_HP=$(cat /proc/sys/vm/nr_hugepages)
echo 10 > /proc/sys/vm/nr_hugepages
NR_HP=$(cat /proc/sys/vm/nr_hugepages)
if [ "$NR_HP" -lt 2 ]; then
echo "SKIP: cannot allocate hugepages"
echo "$OLD_NR_HP" > /proc/sys/vm/nr_hugepages
exit "$UBLK_SKIP_CODE"
fi
# Mount hugetlbfs
HTLB_MNT=$(mktemp -d "${UBLK_TEST_DIR}/htlb_mnt_XXXXXX")
if ! mount -t hugetlbfs none "$HTLB_MNT"; then
echo "SKIP: cannot mount hugetlbfs"
rmdir "$HTLB_MNT"
echo "$OLD_NR_HP" > /proc/sys/vm/nr_hugepages
exit "$UBLK_SKIP_CODE"
fi
HTLB_FILE="$HTLB_MNT/ublk_buf"
fallocate -l 4M "$HTLB_FILE"
_create_backfile 0 128M
BACKFILE="${UBLK_BACKFILES[0]}"
dev_id=$(_add_ublk_dev -t loop --shmem_zc --htlb "$HTLB_FILE" "$BACKFILE")
_check_add_dev $TID $?
_run_fio_verify_io --filename=/dev/ublkb"${dev_id}" \
--size=128M \
--mem=mmaphuge:"$HTLB_FILE"
ERR_CODE=$?
# Delete device first so daemon releases the htlb mmap
_ublk_del_dev "${dev_id}"
rm -f "$HTLB_FILE"
umount "$HTLB_MNT"
rmdir "$HTLB_MNT"
echo "$OLD_NR_HP" > /proc/sys/vm/nr_hugepages
_cleanup_test "shmem_zc"
_show_result $TID $ERR_CODE