[LTP] [PATCH] zram: skip exfat on systems with large page size

[LTP] [PATCH] zram: skip exfat on systems with large page size

[Soma Das]

exfat requires cluster size >= sector size, but defaults to 4KB.
On systems with large page sizes (e.g., 64KB on POWER),
zram uses page size as sector size, causing mkfs.exfat to fail.

Skip exfat filesystem creation when page size > 4096 to avoid test failure.

Signed-off-by: Soma Das <somadas1@linux.ibm.com>
---
 .../kernel/device-drivers/zram/zram01.sh      | 91 +++++++++++++++++++
 1 file changed, 91 insertions(+)

diff --git a/testcases/kernel/device-drivers/zram/zram01.sh b/testcases/kernel/device-drivers/zram/zram01.sh
index 793f6603c..6afba21f0 100755
--- a/testcases/kernel/device-drivers/zram/zram01.sh
+++ b/testcases/kernel/device-drivers/zram/zram01.sh
@@ -11,6 +11,10 @@ TST_TESTFUNC="do_test"
 TST_NEEDS_CMDS="awk bc dd"
 TST_SETUP="setup"
 
+# Track devices that were skipped due to sector size incompatibility
+# Format: space-separated list of device numbers (e.g., "2 5" if zram2 and zram5 were skipped)
+skipped_devices=""
+
 check_space_for_fs()
 {
 	local fs="$1"
@@ -72,15 +76,59 @@ setup()
 	zram_load
 }
 
+check_fs_sector_support()
+{
+	local fs="$1"
+	local dev="$2"
+	local page_size
+	local sector_size
+
+	# Get the system page size - zram uses this as sector size
+	page_size=$(getconf PAGE_SIZE 2>/dev/null)
+	
+	if [ -z "$page_size" ] || [ "$page_size" -lt 4096 ]; then
+		# Default to 4KB if we can't determine page size
+		page_size=4096
+	fi
+
+	tst_res TINFO "check_fs_sector_support: $fs on zram$dev system_page_size=$page_size"
+
+	# CHECK: exfat requires cluster size >= sector size, but defaults to 4KB
+	# On systems with large page sizes (e.g., 64KB on POWER), sector size > 4KB
+	# This causes exfat filesystem creation to fail, so we skip it with TCONF
+	if [ "$fs" = "exfat" ] && [ "$page_size" -gt 4096 ]; then
+		tst_res TINFO "check_fs_sector_support: $fs on zram$dev has page_size=$page_size (> 4096), skipping"
+		return 1  # Return failure (skip this filesystem)
+	fi
+
+	return 0  # All other filesystems pass this check
+}
+
 zram_makefs()
 {
 	local i=$dev_start
 	local fs
+	local sector_size
 
+	# Loop through each filesystem assigned to each zram device
 	for fs in $zram_filesystems; do
+		tst_res TINFO "zram_makefs: checking device zram$i for filesystem $fs"
+		
+		# Check if this filesystem is compatible with the device's sector size
+		if ! check_fs_sector_support "$fs" "$i"; then
+			# Filesystem not supported on this device - mark device as skipped
+			sector_size=$(cat /sys/block/zram${i}/queue/logical_block_size)
+			tst_res TCONF "mkfs.$fs does not support sector size $sector_size"
+			skipped_devices="$skipped_devices $i"  # Add to skipped list
+			i=$(($i + 1))
+			continue  # Skip to next filesystem
+		fi
+
+		# Filesystem is supported - attempt to create it
 		tst_res TINFO "make $fs filesystem on /dev/zram$i"
 		mkfs.$fs /dev/zram$i > err.log 2>&1
 		if [ $? -ne 0 ]; then
+			# Filesystem creation failed
 			cat err.log
 			tst_res TFAIL "Failed to make $fs on /dev/zram$i"
 			tst_brk TBROK "Can't continue with mounting the FS"
@@ -95,8 +143,27 @@ zram_makefs()
 zram_mount()
 {
 	local i
+	local skip
 
+	# Attempt to mount all zram devices
 	for i in $(seq $dev_start $dev_end); do
+		skip=0
+		
+		# Check if this device was marked as skipped during filesystem creation
+		for dev in $skipped_devices; do
+			if [ "$dev" = "$i" ]; then
+				skip=1
+				break
+			fi
+		done
+
+		# Skip mounting devices that don't have filesystems
+		if [ $skip -eq 1 ]; then
+			tst_res TINFO "skipping mount of /dev/zram$i (filesystem not created)"
+			continue
+		fi
+
+		# Mount the filesystem that was created in zram_makefs
 		tst_res TINFO "mount /dev/zram$i"
 		mkdir zram$i
 		ROD mount /dev/zram$i zram$i
@@ -130,8 +197,27 @@ zram_fill_fs()
 {
 	local mem_used_total
 	local b i r v
+	local skip
 
+	# Fill each mounted filesystem with data to test compression
 	for i in $(seq $dev_start $dev_end); do
+		skip=0
+		
+		# Check if this device was marked as skipped (has no filesystem)
+		for dev in $skipped_devices; do
+			if [ "$dev" = "$i" ]; then
+				skip=1
+				break
+			fi
+		done
+
+		# Skip filling devices that don't have filesystems
+		if [ $skip -eq 1 ]; then
+			tst_res TINFO "skipping fill of zram$i (filesystem not created)"
+			continue
+		fi
+
+		# Fill this zram device with zeros to test compression ratio
 		tst_res TINFO "filling zram$i (it can take long time)"
 		b=0
 		while true; do
@@ -140,12 +226,15 @@ zram_fill_fs()
 				>/dev/null 2>err.txt || break
 			b=$(($b + 1))
 		done
+		
+		# Verify that at least some data was written
 		if [ $b -eq 0 ]; then
 			[ -s err.txt ] && tst_res TWARN "dd error: $(cat err.txt)"
 			tst_brk TBROK "cannot fill zram $i"
 		fi
 		tst_res TPASS "zram$i was filled with '$b' KB"
 
+		# Check if compression statistics are available (requires mm_stat)
 		if [ ! -f "/sys/block/zram$i/mm_stat" ]; then
 			if [ $i -eq 0 ]; then
 				tst_res TCONF "zram compression ratio test requires zram mm_stat sysfs file"
@@ -154,6 +243,7 @@ zram_fill_fs()
 			continue
 		fi
 
+		# Read and verify the compression ratio
 		TST_RETRY_FN_EXP_BACKOFF "check_read_mem_used_total /sys/block/zram$i/mm_stat" 0 10
 		mem_used_total=$(read_mem_used_total /sys/block/zram$i/mm_stat)
 		tst_res TINFO "mem_used_total: $mem_used_total"
@@ -161,6 +251,7 @@ zram_fill_fs()
 		v=$((100 * 1024 * $b / $mem_used_total))
 		r=$(echo "scale=2; $v / 100 " | bc)
 
+		# Fail if compression ratio is less than 1:1 (data grew instead of compressed)
 		if [ "$v" -lt 100 ]; then
 			tst_res TFAIL "compression ratio: $r:1"
 			break
-- 
2.39.1


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Re: [LTP] [PATCH] zram: skip exfat on systems with large page size

[Li Wang via ltp]

> exfat requires cluster size >= sector size, but defaults to 4KB.
> On systems with large page sizes (e.g., 64KB on POWER),
> zram uses page size as sector size, causing mkfs.exfat to fail.
> 
> Skip exfat filesystem creation when page size > 4096 to avoid test failure.

Or, can we specify the sector size with 'mkfs.$fs -c $page_size'
when detecting a large pagesize system?

-- 
Regards,
Li Wang


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Re: [LTP] [PATCH] zram: skip exfat on systems with large page size

[Soma Das]

On Fri, Apr 03, 2026 at 09:47:33AM +0800, Li Wang wrote:
> Or, can we specify the sector size with 'mkfs.$fs -c $page_size'
> when detecting a large pagesize system?

Thanks for the review.

Using mkfs.exfat -c $page_size would technically work, but I avoided
it because:

1. zram01 tests zram behaviour, not filesystem configuration -- using
   a non-default cluster size feels out of scope.
2. The cluster size must be valid for the disk size (only 25MB here),
   so large cluster sizes could hit additional constraints.

Skipping with TCONF honestly reflects that default exfat tooling does
not support this hardware configuration, which is useful signal.

Happy to send a v2 with the -c approach if you prefer.

Thanks,
Soma

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Re: [LTP] [PATCH] zram: skip exfat on systems with large page size

[Li Wang via ltp]

Thanks for the explanation.

I still think we should go with the -c approach rather than skipping.
A couple of points:

On 1, I don't think this changes the scope of the test. zram01 already
invokes mkfs.$fs as a means to exercise zram, adjusting a parameter so
that mkfs actually succeeds is just making the test work, not turning
it into a filesystem configuration test.

On 2, 25MB with a 64KB cluster size gives roughly 390 clusters, which
is well within exfat's limits. Could you point out a concrete constraint
that would actually fail here? If there isn't one, I'd prefer not to
use a hypothetical concern as justification for skipping.

On the TCONF, reporting TCONF here would make it look like exfat on
zram is fundamentally broken on 64K-page systems, when in reality it
works with a one-line change. That is a false negative we should
avoid in a test suite.

Please send a v2 with the -c approach.

On Fri, Apr 03, 2026 at 04:59:47PM +0000, Soma Das wrote:
> On Fri, Apr 03, 2026 at 09:47:33AM +0800, Li Wang wrote:
> > Or, can we specify the sector size with 'mkfs.$fs -c $page_size'
> > when detecting a large pagesize system?
> 
> Thanks for the review.
> 
> Using mkfs.exfat -c $page_size would technically work, but I avoided
> it because:
> 
> 1. zram01 tests zram behaviour, not filesystem configuration -- using
>    a non-default cluster size feels out of scope.
> 2. The cluster size must be valid for the disk size (only 25MB here),
>    so large cluster sizes could hit additional constraints.
> 
> Skipping with TCONF honestly reflects that default exfat tooling does
> not support this hardware configuration, which is useful signal.
> 
> Happy to send a v2 with the -c approach if you prefer.
> 
> Thanks,
> Soma
> 

-- 
Regards,
Li Wang


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Re: [LTP] [PATCH] zram: skip exfat on systems with large page size

[Soma Das]

On Sat, Apr 04, 2026 at 09:14:32AM +0800, Li Wang wrote:
> I still think we should go with the -c approach rather than skipping.

Thanks for the detailed explanation.

Understood — I will send a v2 with the -c $page_size approach.

Thanks,
Soma

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