Hi,
I was testing the filesystem performance of my system using the
following script:
#!/bin/bash
while true;
do
dd if=/dev/zero of=output.dat bs=100M count=1
done
I noticed that after some time, all the physical memory is consumed by
the LRU inactive list and only 120 MB are left to the system.
/proc/meminfo shows the following information:
MemTotal: 4021820 Kb
MemFree: 121912 Kb
Active: 1304396 Kb
Inactive: 2377124 Kb
The evolution of memory utilization over time is available in this link:
http://secretaire.dorsal.polymtl.ca/~hdaoud/ext4_journal_meminfo.png
With the help of a kernel tracer, I found that most of the pages in the
inactive list are created by the ext4 journal during a truncate operation.
The call stack of the allocation is:
[
__alloc_pages_nodemask
alloc_pages_current
__page_cache_alloc
find_or_create_page
__getblk
jbd2_journal_get_descriptor_buffer
jbd2_journal_commit_transaction
kjournald2
kthread
]
I can't find an explanation why the LRU is growing while we are just
writing to the same file again and again. I know that the philosophy of
memory management in Linux is to use the available memory as much as
possible, but what is the need of keeping truncated pages in the LRU if
we know that they are not even accessible ?
Thanks !
ps: My system is running kernel 4.3 with ext4 filesystem (journal mode)
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