> Hi Minchan, > > On Mon, Nov 07, 2022 at 08:11:35PM +0100, Petr Vorel wrote: > > > Hi all, > > > following bug is trying to workaround an error on ppc64le, where > > > zram01.sh LTP test (there is also kernel selftest > > > tools/testing/selftests/zram/zram01.sh, but LTP test got further > > > updates) has often mem_used_total 0 although zram is already filled. > > Hi, Petr, > > Is it happening on only ppc64le? > I haven't seen it on other archs (x86_64, aarch64). > > Is it a new regression? What kernel version did you use? > Found on openSUSE kernel, which uses stable kernel releases 6.0.x. > It's probably much older, first I've seen it some years ago (I'm not able to find kernel version), but it was random. Now it's much more common. I tested it on bare metal machine with some older SLES kernel (based on 4.12.14, with thousands of patches) and it fails: # PATH="/opt/ltp/testcases/bin:$PATH" LTP_SINGLE_FS_TYPE=vfat zram01.sh ... zram01 5 TINFO: make vfat filesystem on /dev/zram0 zram01 5 TPASS: zram_makefs succeeded zram01 6 TINFO: mount /dev/zram0 zram01 6 TPASS: mount of zram device(s) succeeded zram01 7 TINFO: filling zram0 (it can take long time) zram01 7 TPASS: zram0 was filled with '25568' KB /opt/ltp/testcases/bin/zram01.sh: line 137: 100 * 1024 * 25568 / 0: division by 0 (error token is "0") ... My patch does not help, obviously the value does not change. zram01 5 TINFO: make vfat filesystem on /dev/zram1 zram01 5 TPASS: zram_makefs succeeded zram01 6 TINFO: mount /dev/zram1 zram01 6 TPASS: mount of zram device(s) succeeded zram01 7 TINFO: filling zram1 (it can take long time) zram01 7 TPASS: zram1 was filled with '25568' KB zram01 7 TINFO: /sys/block/zram1/mm_stat 15859712 0 0 26214400 196608 242 0 zram01 7 TINFO: /sys/block/zram1/mm_stat 15859712 0 0 26214400 196608 242 0 zram01 7 TINFO: /sys/block/zram1/mm_stat 15859712 0 0 26214400 196608 242 0 zram01 7 TINFO: /sys/block/zram1/mm_stat 15859712 0 0 26214400 196608 242 0 zram01 7 TINFO: /sys/block/zram1/mm_stat 15859712 0 0 26214400 196608 242 0 zram01 7 TINFO: /sys/block/zram1/mm_stat 15859712 0 0 26214400 196608 242 0 zram01 7 TINFO: /sys/block/zram1/mm_stat 15859712 0 0 26214400 196608 242 0 zram01 7 TINFO: /sys/block/zram1/mm_stat 15859712 0 0 26214400 196608 242 0 zram01 7 TINFO: /sys/block/zram1/mm_stat 15859712 0 0 26214400 196608 242 0 zram01 7 TINFO: /sys/block/zram1/mm_stat 15859712 0 0 26214400 196608 242 0 zram01 7 TINFO: /sys/block/zram1/mm_stat 15859712 0 0 26214400 196608 242 0 zram01 7 TINFO: /sys/block/zram1/mm_stat 15859712 0 0 26214400 196608 242 0 zram01 7 TINFO: /sys/block/zram1/mm_stat 15859712 0 0 26214400 196608 242 0 zram01 7 TINFO: /sys/block/zram1/mm_stat 15859712 0 0 26214400 196608 242 0 zram01 7 TINFO: /sys/block/zram1/mm_stat 15859712 0 0 26214400 196608 242 0 zram01 7 TINFO: /sys/block/zram1/mm_stat 15859712 0 0 26214400 196608 242 0 zram01 7 TINFO: /sys/block/zram1/mm_stat 15859712 0 0 26214400 196608 242 0 zram01 7 TINFO: /sys/block/zram1/mm_stat 15859712 0 0 26214400 196608 242 0 zram01 7 TINFO: /sys/block/zram1/mm_stat 15859712 0 0 26214400 196608 242 0 zram01 7 TINFO: /sys/block/zram1/mm_stat 15859712 0 0 26214400 196608 242 0 zram01 7 TINFO: /sys/block/zram1/mm_stat 15859712 0 0 26214400 196608 242 0 zram01 7 TBROK: "loop_read_mem_used_total /sys/block/zram1/mm_stat" timed out This is just to demonstrate, that the problem has been here long time, and it's not QEMU related (although it could be theoretically related to openSUSE/SLES user space, but it's very unlikely). I'll debug if page_same_filled() is being called on mainline kernel. Kind regards, Petr > Test runs on VM (I can give qemu command or whatever you need to know about it) > I'll try to verify it on some bare metal ppc64le. > > Actually, mem_used_total indicates how many *physical memory* were > > currently used to keep original data size. > > However, if the test data is repeated pattern of unsigned long > > (https://github.com/torvalds/linux/blob/master/drivers/block/zram/zram_drv.c#L210) > > zram doesn't allocate the physical memory but just mark the unsigned long's value > > in meta area for decompression later. > > Not sure you hit the this case. > Thanks for a hint, I'll try to debug it. > Kind regards, > Petr > > > Patch tries to repeatedly read /sys/block/zram*/mm_stat for 1 sec, > > > waiting for mem_used_total > 0. The question if this is expected and > > > should be workarounded or a bug which should be fixed. > > > REPRODUCE THE ISSUE > > > Quickest way to install only zram tests and their dependencies: > > > make autotools && ./configure && for i in testcases/lib/ testcases/kernel/device-drivers/zram/; do cd $i && make -j$(getconf _NPROCESSORS_ONLN) && make install && cd -; done > > > Run the test (only on vfat) > > > PATH="/opt/ltp/testcases/bin:$PATH" LTP_SINGLE_FS_TYPE=vfat zram01.sh > > > Petr Vorel (1): > > > zram01.sh: Workaround division by 0 on vfat on ppc64le > > > .../kernel/device-drivers/zram/zram01.sh | 27 +++++++++++++++++-- > > > 1 file changed, 25 insertions(+), 2 deletions(-) > > > -- > > > 2.38.0
