The age extent cache uses last_blocks (derived from allocated_data_blocks) to determine data age. However, there's a conflict between the deletion marker (last_blocks=0) and legitimate last_blocks=0 cases when allocated_data_blocks overflows to 0 after reaching ULLONG_MAX. In this case, valid extents are incorrectly skipped due to the "if (!tei->last_blocks)" check in __update_extent_tree_range(). This patch fixes the issue by: 1. Reserving ULLONG_MAX as an invalid/deletion marker 2. Limiting allocated_data_blocks to range [0, ULLONG_MAX-1] 3. Using F2FS_EXTENT_AGE_INVALID for deletion scenarios 4. Adjusting overflow age calculation from ULLONG_MAX to (ULLONG_MAX-1) Reproducer (using a patched kernel with allocated_data_blocks initialized to ULLONG_MAX - 3 for quick testing): Step 1: Mount and check initial state # dd if=/dev/zero of=/tmp/test.img bs=1M count=100 # mkfs.f2fs -f /tmp/test.img # mkdir -p /mnt/f2fs_test # mount -t f2fs -o loop,age_extent_cache /tmp/test.img /mnt/f2fs_test # cat /sys/kernel/debug/f2fs/status | grep -A 4 "Block Age" Allocated Data Blocks: 18446744073709551612 # ULLONG_MAX - 3 Inner Struct Count: tree: 1(0), node: 0 Step 2: Create files and write data to trigger overflow # touch /mnt/f2fs_test/{1,2,3,4}.txt; sync # cat /sys/kernel/debug/f2fs/status | grep -A 4 "Block Age" Allocated Data Blocks: 18446744073709551613 # ULLONG_MAX - 2 Inner Struct Count: tree: 5(0), node: 1 # dd if=/dev/urandom of=/mnt/f2fs_test/1.txt bs=4K count=1; sync # cat /sys/kernel/debug/f2fs/status | grep -A 4 "Block Age" Allocated Data Blocks: 18446744073709551614 # ULLONG_MAX - 1 Inner Struct Count: tree: 5(0), node: 2 # dd if=/dev/urandom of=/mnt/f2fs_test/2.txt bs=4K count=1; sync # cat /sys/kernel/debug/f2fs/status | grep -A 4 "Block Age" Allocated Data Blocks: 18446744073709551615 # ULLONG_MAX Inner Struct Count: tree: 5(0), node: 3 # dd if=/dev/urandom of=/mnt/f2fs_test/3.txt bs=4K count=1; sync # cat /sys/kernel/debug/f2fs/status | grep -A 4 "Block Age" Allocated Data Blocks: 0 # Counter overflowed! Inner Struct Count: tree: 5(0), node: 4 Step 3: Trigger the bug - next write should create node but gets skipped # dd if=/dev/urandom of=/mnt/f2fs_test/4.txt bs=4K count=1; sync # cat /sys/kernel/debug/f2fs/status | grep -A 4 "Block Age" Allocated Data Blocks: 1 Inner Struct Count: tree: 5(0), node: 4 Expected: node: 5 (new extent node for 4.txt) Actual: node: 4 (extent insertion was incorrectly skipped due to last_blocks = allocated_data_blocks = 0 in __get_new_block_age) After this fix, the extent node is correctly inserted and node count becomes 5 as expected. Fixes: 71644dff4811 ("f2fs: add block_age-based extent cache") Cc: stable@kernel.org Signed-off-by: Xiaole He <hexiaole1994@126.com> Reviewed-by: Chao Yu <chao@kernel.org> Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>