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swap: speed up preferring a 1MiB blocksize

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If the swap disk is larger than 1MiB, then use a 1MiB blocksize in `dd`

On my machine using a large block size speeds up swap file creation:

```
/ # time dd if=/dev/zero of=output bs=1024 count=1048576
1048576+0 records in
1048576+0 records out
real    0m 4.61s
user    0m 0.79s
sys     0m 3.77s
/ # time dd if=/dev/zero of=output bs=1048576 count=1024
1024+0 records in
1024+0 records out
real    0m 1.06s
user    0m 0.00s
sys     0m 1.04s
```

Signed-off-by: David Scott <dave.scott@docker.com>
This commit is contained in:
David Scott 2019-11-22 20:31:27 +00:00
parent 4092a10063
commit 57dd4029c8
1 changed files with 6 additions and 1 deletions
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7
pkg/swap/swap.sh
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@ -123,7 +123,12 @@ fi
if [ ! -f $path ] || ! [ $(stat -c "%s" $path) == $(disksize_to_count 1 $size) ]; then
## Allocate the file
dd if=/dev/zero of=$path bs=1024 count=$(disksize_to_count 1024 $size)
## If possible use a large blocksize:
bs=1048576 # 1 MiB
if [ "$size" -lt "$bs" ]; then
bs=1024 # fall back to 1KiB
fi
dd if=/dev/zero of=$path bs=$bs count=$(disksize_to_count $bs $size)
chmod 0600 $path
## was it encrypted? use cryptsetup and get the mapped device