On 2019/6/22 下午11:11, Andrei Borzenkov wrote: [snip] > > 10:/mnt # dd if=/dev/urandom of=test/file bs=1M count=100 seek=0 > conv=notrunc > 100+0 records in > 100+0 records out > 104857600 bytes (105 MB, 100 MiB) copied, 0.685532 s, 153 MB/s > 10:/mnt # sync > 10:/mnt # btrfs qgroup show . > qgroupid rfer excl > -------- ---- ---- > 0/5 16.00KiB 16.00KiB > 0/258 1.01GiB 100.02MiB > 0/263 1.00GiB 85.02MiB
Sorry, I can't really reproduce it. 5.1.12 kernel, using the following script: --- #!/bin/bash dev="/dev/data/btrfs" mnt="/mnt/btrfs" umount $dev &> /dev/null mkfs.btrfs -f $dev > /dev/null mount $dev $mnt btrfs sub create $mnt/subv1 btrfs quota enable $mnt btrfs quota rescan -w $mnt xfs_io -f -c "pwrite 0 1G" $mnt/subv1/file1 sync btrfs sub snapshot $mnt/subv1 $mnt/subv2 sync btrfs qgroup show -prce $mnt xfs_io -c "pwrite 0 100m" $mnt/subv1/file1 sync btrfs qgroup show -prce $mnt --- The result is: --- Create subvolume '/mnt/btrfs/subv1' wrote 1073741824/1073741824 bytes at offset 0 1 GiB, 262144 ops; 0.5902 sec (1.694 GiB/sec and 444134.2107 ops/sec) Create a snapshot of '/mnt/btrfs/subv1' in '/mnt/btrfs/subv2' qgroupid rfer excl max_rfer max_excl parent child -------- ---- ---- -------- -------- ------ ----- 0/5 16.00KiB 16.00KiB none none --- --- 0/256 1.00GiB 16.00KiB none none --- --- 0/259 1.00GiB 16.00KiB none none --- --- wrote 104857600/104857600 bytes at offset 0 100 MiB, 25600 ops; 0.0694 sec (1.406 GiB/sec and 368652.9766 ops/sec) qgroupid rfer excl max_rfer max_excl parent child -------- ---- ---- -------- -------- ------ ----- 0/5 16.00KiB 16.00KiB none none --- --- 0/256 1.10GiB 100.02MiB none none --- --- 0/259 1.00GiB 16.00KiB none none --- --- --- > 10:/mnt # filefrag -v test/file > Filesystem type is: 9123683e > File size of test/file is 1073741824 (262144 blocks of 4096 bytes) > ext: logical_offset: physical_offset: length: expected: flags: > 0: 0.. 22463: 315424.. 337887: 22464: There is a initial 10.9MiB extent, I'm not sure how it's created. > 1: 22464.. 25599: 76896.. 80031: 3136: 337888: Also here comes another 1.5MiB extent. From the result of the fiemap, it's definitely not 100MiB written. Only 12.5M written. The fiemap result doesn't match with your dd command. Any clue how this happened? Thanks, Qu > 2: 25600.. 43135: 59264.. 76799: 17536: 80032: shared > 3: 43136.. 97279: 86048.. 140191: 54144: 76800: shared > 4: 97280.. 151551: 143392.. 197663: 54272: 140192: shared > 5: 151552.. 207359: 200736.. 256543: 55808: 197664: shared > 6: 207360.. 262143: 258080.. 312863: 54784: 256544: > last,shared,eof > test/file: 7 extents found > 10:/mnt # filefrag -v snap1/file > Filesystem type is: 9123683e > File size of snap1/file is 1073741824 (262144 blocks of 4096 bytes) > ext: logical_offset: physical_offset: length: expected: flags: > 0: 0.. 43135: 33664.. 76799: 43136: > 1: 43136.. 97279: 86048.. 140191: 54144: 76800: shared > 2: 97280.. 151551: 143392.. 197663: 54272: 140192: shared > 3: 151552.. 207359: 200736.. 256543: 55808: 197664: shared > 4: 207360.. 262143: 258080.. 312863: 54784: 256544: > last,shared,eof > snap1/file: 5 extents found > > > Oops. Where 85MiB exclusive usage in snapshot comes from? I would expect > one of > > - 0 exclusive, because original first extent is still referenced by test > (even though partially), so if qgroup counts physical space usage, snap1 > effectively refers to the same physical extents as test. > > - 100MiB exclusive if qgroup counts logical space consumption, because > snapshot now has 100MiB different data. > > But 85MiB? It does not match any observed value. Judging by 1.01GiB of > referenced space for subvolume test, qrgoup counts physical usage, at > which point snapshot exclusive space consumption remains 0. >
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