Re: Applying nice/ionice to nilfs-cleanerd

[dexen deVries <dexen.devries-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

On Monday 08 of August 2011 01:23:19 you wrote:
> At present, you have to manually invoke the cleanerd through the
> nice/ionice commands or to run renice/ionice later specifying the
> process ID of the cleanerd.
> 
> One way to make this convenient is introducing new directives in
> /etc/nilfs_cleanerd.conf as follows:
> 
>  # Scheduling priority.
>  nice 19    # niceness -20~19
> 
>  # IO scheduling class.
>  # Supported classes are default, idle, best-effort, and realtime.
>  ionice_class  idle
> 
>  # IO scheduling priority.
>  # 0-7 is valid for best-effort and realtime classes.
>  ionice_data   5
> 
> Do you think these extensions make sense ?


it would be nice (hehe) to be able to temporarily lower cleanerd priority when 
watching a movie or building software. 

However, may be a downside to /always/ running cleanerd niced and ioniced.  I 
believe that currently cleanerd's activity slows other processes down a lot 
when filesystem is almost full -- which means that it oftet won't become truly 
full, because clearned will free enough space for other processes to be able 
to complete their work. If, on the other hand, cleanerd was highly niced and 
ioniced, it could end up being starved of CPU and disk bandwidth and not 
freeing enough free space, which could cause other processes to exhaust free 
space on filesystem and abord when not able to write to filesystem.

Perhaps it would be enough to have cleanerd automatically switch priority 
based on available free space. For example, if I had
min_clean_segments      10%
max_clean_segments      12%

then also have
min_clean_segments_low_prio	8%

low_prio_nice 19
normal_prio_nice 0

low_prio_ionice_class idle
normal_prio_ionice_class realtime

which woud mean, `use low priority (nice & ionice) when there's at least 8% of 
free segments; if there's less use higher priority' -- so cleanerd would 
reclaim free space more aggressively when there's little free space left.


Cheers,
-- 
dexen deVries

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