[BUG]
When running the test case btrfs/002, with 64K page size and 64K sector
size, and the VM doesn't have much memory (in my case 4G Vram), the test
case will trigger OOM and fail:
btrfs/002 4s ... [failed, exit status 1]- output mismatch (see /home/adam/xfstests-dev/results//btrfs/002.out.bad)
--- tests/btrfs/002.out 2024-04-25 18:13:45.035555469 +0930
+++ /home/adam/xfstests-dev/results//btrfs/002.out.bad 2024-10-12 17:19:48.785156223 +1030
@@ -1,2 +1 @@
QA output created by 002
-Silence is golden
...
The OOM is triggered by the dd process, and a lot of dd processes are
using too much memory:
dd invoked oom-killer: gfp_mask=0x140dca(GFP_HIGHUSER_MOVABLE|__GFP_COMP|__GFP_ZERO), order=0, oom_score_adj=250
CPU: 0 UID: 0 PID: 185764 Comm: dd Not tainted 6.12.0-rc2-custom+ #76
Hardware name: QEMU KVM Virtual Machine, BIOS unknown 2/2/2022
Tasks state (memory values in pages):
[ pid ] uid tgid total_vm rss rss_anon rss_file rss_shmem pgtables_bytes swapents oom_score_adj name
[ 185665] 0 185665 8688 3840 3840 0 0 458752 4832 250 dd
[ 185672] 0 185672 8688 2432 2432 0 0 393216 5312 250 dd
[ 185680] 0 185680 8688 2016 2016 0 0 458752 4960 250 dd
[ 185686] 0 185686 8688 2080 2080 0 0 458752 3584 250 dd
[ 185693] 0 185693 8688 2144 2144 0 0 458752 4384 250 dd
[ 185700] 0 185700 8688 2176 2176 0 0 458752 3584 250 dd
[ 185707] 0 185707 8688 1792 1792 0 0 524288 3616 250 dd
[ 185714] 0 185714 8688 2304 2304 0 0 458752 3488 250 dd
[ 185721] 0 185721 8688 1920 1920 0 0 458752 2624 250 dd
[ 185728] 0 185728 8688 2272 2272 0 0 393216 2528 250 dd
[ 185735] 0 185735 8688 2048 2048 0 0 393216 3552 250 dd
[ 185742] 0 185742 8688 1984 1984 0 0 458752 2816 250 dd
[ 185751] 0 185751 8688 1600 1600 0 0 458752 2784 250 dd
[ 185756] 0 185756 8688 1120 1120 0 0 458752 2400 250 dd
[ 185764] 0 185764 8688 1504 1504 0 0 393216 2240 250 dd
[ 185772] 0 185772 8688 1504 1504 0 0 458752 1984 250 dd
[ 185777] 0 185777 8688 1280 1280 0 0 393216 2336 250 dd
[ 185784] 0 185784 8688 2144 2144 0 0 393216 2272 250 dd
[ 185791] 0 185791 8688 2176 2176 0 0 458752 576 250 dd
[ 185798] 0 185798 8688 1696 1696 0 0 458752 1536 250 dd
[ 185806] 0 185806 8688 1728 1728 0 0 393216 544 250 dd
[ 185815] 0 185815 8688 2240 2240 0 0 458752 0 250 dd
[ 185819] 0 185819 8688 1504 1504 0 0 458752 384 250 dd
[ 185826] 0 185826 8688 1536 1536 0 0 458752 160 250 dd
[ 185833] 0 185833 8688 2944 2944 0 0 458752 64 250 dd
[ 185838] 0 185838 8688 2400 2400 0 0 458752 0 250 dd
[ 185847] 0 185847 8688 864 864 0 0 458752 0 250 dd
[ 185853] 0 185853 8688 1088 1088 0 0 393216 0 250 dd
[ 185860] 0 185860 8688 416 416 0 0 393216 0 250 dd
[ 185867] 0 185867 8688 352 352 0 0 458752 0 250 dd
[CAUSE]
The test case workload _fill_blk() is going to fill the file to its block
boundary.
But the implementation is not taking larger blocks into consideration.
FSIZE=`stat -t $i | cut -d" " -f2`
BLKS=`stat -c "%B" $i`
NBLK=`stat -c "%b" $i`
FALLOC=$(($BLKS * $NBLK))
WS=$(($FALLOC - $FSIZE))
$FSIZE is the file size, $BLKS is the size of each reported block,
$NBLK is the number of blocks the file takes, thus $FALLOC is the
rounded up block size.
For 64K sector size, the BLKS is 512, and BLKS is 128 (one 64K sector).
$FALLOC is the correct value of 64K (10K rounded up to 64K).
Then the problem comes to how the write is done:
_ddt of=$i oseek=$FSIZE obs=$WS count=1 status=noxfer 2>/dev/null &
Unfrotunately the above command is using output block size of 54K, and
need to skip 10K * 54K bytes, resulting a file size of 540M.
So far although it's not the correct intention, it's not yet causing
problem.
But during _append_file(), we further enlarge the file by:
FSIZE=`stat -t $i | cut -d" " -f2`
dd if=$X of=$i seek=1 bs=$FSIZE obs=$FSIZE count=1 status=noxfer 2>/dev/null &
In above case, since the previous file is 540M size, the output block
size will also be 540M, taking a lot of memory.
Furthermore since the workload is run in background, we can have many dd
processes taking up at least 540M, causing huge memory usage and trigger
OOM.
[FIX]
The original code is already not doing what it should do, just get rid of
the cursed dd command usage inside _fill_blk(), and use pwrite from
xfs_io instead.
Signed-off-by: Qu Wenruo <wqu@xxxxxxxx>
---
tests/btrfs/002 | 14 +++++---------
1 file changed, 5 insertions(+), 9 deletions(-)
diff --git a/tests/btrfs/002 b/tests/btrfs/002
index f223cc60..0c231b89 100755
--- a/tests/btrfs/002
+++ b/tests/btrfs/002
@@ -70,19 +70,14 @@ _read_modify_write()
_fill_blk()
{
local FSIZE
- local BLKS
- local NBLK
- local FALLOC
- local WS
+ local NEWSIZE
for i in `find /$1 -type f`
do
FSIZE=`stat -t $i | cut -d" " -f2`
- BLKS=`stat -c "%B" $i`
- NBLK=`stat -c "%b" $i`
- FALLOC=$(($BLKS * $NBLK))
- WS=$(($FALLOC - $FSIZE))
- _ddt of=$i oseek=$FSIZE obs=$WS count=1 status=noxfer 2>/dev/null &
+ NEWSIZE=$(( ($FSIZE + $blksize -1 ) / $blksize * $blksize ))
+
+ $XFS_IO_PROG -c "pwrite -i /dev/urandom $FSIZE $(( $NEWSIZE - $FSIZE ))" $i > /dev/null &
done
wait $!
}
@@ -118,6 +113,7 @@ $BTRFS_UTIL_PROG subvolume create $firstvol > /dev/null || _fail "btrfs subvolum
dirp=`mktemp -duq $firstvol/dir.XXXXXX`
_populate_fs -n 1 -f 20 -d 10 -r $dirp -s 10 -c
SNAPNAME=0
+blksize=$(_get_block_size $SCRATCH_MNT)
_create_snap $firstvol
_save_checksum $firstvol $tmp.sv1.sum
_verify_checksum $SNAPNAME $tmp.sv1.sum
--
2.47.0
