Page fault once the GC is triggered

[praths21]

Issue description: After running db_bench with fillrandom workload, after garbage collecting a few zones, the system always hit the page fault.

Environment Terarkdb: 1.4 ZenFS Version: latest version Operating System: Linux debian 5.10 Hardware Configuration: 3.2TB ZNS SSD and 16GB DRAM

Script to reproduce:

1. zenfs mkfs --zbd=$DEVICE --auxpath=/tmp/zbd$DEVICE --force=true --enable_gc=true
2. db_bench \ --zbd_path=$DEVICE \ --benchmarks=fillrandom\ --readwritepercent=99 \ --histogram=1 \ --statistics=1 \ --enable_lazy_compaction=0 \ --level0_file_num_compaction_trigger=4 \ --sync=1 \ --wal_bytes_per_sync=32768 \ --threads=16 \ --num_levels=7 \ --key_size=36 \ --value_size=20000 \ --level_compaction_dynamic_level_bytes=true \ --mmap_read=false \ --use_terark_table=false \ --blob_size=1024 \ --blob_gc_ratio=0.0625 \ --num=548768010 \ --max_write_buffer_number=20 \ --benchmark_write_rate_limit=300000000 \ --batch_size=100 \ --disable_auto_compactions \ --db=test_fill \ --disable_auto_compactions \ --write_buffer_size=536870912 \ --zenfs_low_gc_ratio=0.3 \ --zenfs_high_gc_ratio=0.6 \ --zenfs_force_gc_ratio=0.9

Here is the following call trace.

debian kernel: [26158.433496][T19093] Call Trace: debian kernel: [26158.433502][T19093] dump_stack+0x6d/0x88 debian kernel: [26158.433503][T19093] dump_header+0x4a/0x1e4 debian kernel: [26158.433504][T19093] oom_kill_process.cold.37+0xb/0x10 debian kernel: [26158.433505][T19093] out_of_memory+0x1a8/0x4e0 debian kernel: [26158.433507][T19093] alloc_pages_slowpath.constprop.106+0xb29/0xc10 debian kernel: [26158.433508][T19093] alloc_pages_nodemask+0x2cc/0x300 debian kernel: [26158.433509][T19093] pagecache_get_page.part.62+0xe2/0x440 debian kernel: [26158.433510][T19093] filemap_fault+0x6a7/0xa10 debian kernel: [26158.433512][T19093] ? xas_load+0x8/0x80 debian kernel: [26158.433524][T19093] ext4_filemap_fault+0x2c/0x40 [ext4] debian kernel: [26158.433526][T19093] __do_fault+0x30/0x100 debian kernel: [26158.433527][T19093] handle_mm_fault+0x1201/0x1600 debian kernel: [26158.433529][T19093] do_user_addr_fault+0x1b0/0x5c0 debian kernel: [26158.433530][T19093] exc_page_fault+0x7f/0x170 debian kernel: [26158.433532][T19093] ? asm_exc_page_fault+0x8/0x30 debian kernel: [26158.433532][T19093] asm_exc_page_fault+0x1e/0x30