fio memory allocation problems

[Jiri Horky <jiri.horky@cesnet.cz>]

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Hi,

I think I found a bug. If the device (file) used in fio has "wrong" 
size, and is used with "wrong" block size, the fio fails to allocate 
memory for randommap.
Following conditions must be true, considering just one thread for 
simplicity:

  1) number of blocks on the device are too big to fill in the default's 
pool
  2) number of blocks on the device must be "right", so the size of 
newly allocated pool by smalloc.c:add_pool is exactly as big as 
requested size (there are some roundings in place, so not every size 
triggers this error)

When this is true, function smalloc.c:__smalloc_pool fails to use the 
newly created (exactly big enough) pool, because of this line:

                 idx = find_next_zero(pool->bitmap[i], last_idx);

which always returns non-zero value (the minimum returned value is 
last_idx +1), and so in our case the idx is 1 even though, the block 
number 0 is free. As the direct consequence, the function doesn't find 
enough free space in the given pool and returns NULL pointer. This leads 
to another try to allocate enough memory in smalloc.c:smalloc_real 
function, and so on...

The behavior could be reprocuded using both stable 1.57 and git version 
of the tool. The values that triggers the error are:
init_random_map - real_file_size: 21999995584512, o.rw_min_bs: 4096, 
blocks: 5371092672, num_maps: 83923323, alloc size: 671386584

whereas this block device is fine:
init_random_map - real_file_size: 19999995985920, o.rw_min_bs: 4096, 
blocks: 4882811520, num_maps: 76293930, alloc size: 610351440

the configuration file used:

[global]
description=CESNET_test
[cesnet]
filename=/dev/sdd
rw=randread
size=10000g
ioengine=libaio
iodepth=4
bs=4k
runtime=10m
time_based
numjobs=1
#norandommap
group_reporting


I am not sure I fully understand all the logic in smalloc.c so I am 
afraid I would break something with a trivial patch.

Let me know, if you need more information

Best Regards
Jiri Horky






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