Re: Unexpected growth of the LRU inactive list

[Michal Hocko <mhocko@kernel.org>]

[CC ext/jbd experts]

On Wed 13-07-16 01:48:57, Houssem Daoud wrote:
> 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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-- 
Michal Hocko
SUSE Labs

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