On Wed, Oct 17, 2018 at 11:20:58AM +0300, Vladimir Davydov wrote:
Anyway, you seem to be unaware of the fact that one of fallocate use
cases is speeding writes by reducing the number of file size updates
(which require a write to the inode table). I wrote a simple test that
demonstrates that, see below.
vlad@esperanza test$ gcc -O2 fallocate_test.c -o fallocate_test
vlad@esperanza test$ ./fallocate_test
Usage: ./fallocate_test <filename> <write_count> <write_size> <alloc_size>
filename - test file
write_count - number of writes (append)
write_size - write(2) size
alloc_size - fallocate(2) size
returns time in seconds
vlad@esperanza test$ ./fallocate_test dummy 1000000 100 0
1.548161
vlad@esperanza test$ ./fallocate_test dummy 1000000 100 0
1.505698
vlad@esperanza test$ ./fallocate_test dummy 1000000 100 100000
1.195223
vlad@esperanza test$ ./fallocate_test dummy 1000000 100 100000
1.137996
I have stock ext4 over hdd on my laptop, configured by Debian, no
tuning. The code is right below. That is for an append-only workload
similar to WAL fallocate yields ~25% gain.
