Eric Sandeen wrote:
Lachlan McIlroy wrote:
Eric Sandeen wrote:
Eric Sandeen wrote:
Gah; or not. what is going on here... Doing just steps 1, 2, 3, 4
(ending on the extending truncate):
# xfs_io -c "pwrite -S 0x11 -b 4096 0 4096" -c "mmap -r 0 512" -c "mread
0 512" -c "munmap" -c "truncate 256" -c "truncate 514" -t -d -f
/mnt/scratch/testfile
# xfs_bmap -v /mnt/scratch/testfile
/mnt/scratch/testfile:
EXT: FILE-OFFSET BLOCK-RANGE AG AG-OFFSET TOTAL
0: [0..0]: 63..63 0 (63..63) 1
1: [1..1]: hole 1
It looks like what I expect, at this point. But then:
# sync
# xfs_bmap -v /mnt/scratch/testfile
/mnt/scratch/testfile:
EXT: FILE-OFFSET BLOCK-RANGE AG AG-OFFSET TOTAL
0: [0..1]: 63..64 0 (63..64) 2
Um, why'd that last block get mapped in? mmap vs. direct IO I'm
guessing... w/o the mmap read this does not happen.
Replying to myself twice? I really need to go to bed.
So this all does seem to come back to page_state_convert.
Both the extending write in the original case and the sync above find
their way there; but esp. in the sync test above, why do we have *any*
work to do?
Eric, did you find out why sync was allocating that second block?
I'm afraid this has been on the back burner (or maybe further back) for
a while... so... either "no" or "I don't remember" :)
Just trying your test case. It's not related to direct I/O or mmap I/O
since I can reproduce it without those.
# xfs_io -f -c "pwrite -S 0x11 -b 513 0 513" -c "truncate 1" -c "truncate 513"
file
wrote 513/513 bytes at offset 0
513.000000 bytes, 1 ops; 0.0000 sec (8.895 MiB/sec and 18181.8182 ops/sec)
# xfs_bmap -vvp file; sync; xfs_bmap -vvp file
file:
EXT: FILE-OFFSET BLOCK-RANGE AG AG-OFFSET TOTAL FLAGS
0: [0..0]: 48..48 0 (48..48) 1 00000
1: [1..1]: hole 1
FLAG Values:
010000 Unwritten preallocated extent
001000 Doesn't begin on stripe unit
000100 Doesn't end on stripe unit
000010 Doesn't begin on stripe width
000001 Doesn't end on stripe width
file:
EXT: FILE-OFFSET BLOCK-RANGE AG AG-OFFSET TOTAL FLAGS
0: [0..1]: 48..49 0 (48..49) 2 00000
FLAG Values:
010000 Unwritten preallocated extent
001000 Doesn't begin on stripe unit
000100 Doesn't end on stripe unit
000010 Doesn't begin on stripe width
000001 Doesn't end on stripe width
xfs_bmap will cause the file to be flushed so there should be no dirty
data to be flushed during the sync. Strange.
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