On Tue 10-07-18 12:09:17, Waiman Long wrote:

On 07/10/2018 10:27 AM, Michal Hocko wrote:

quoted

On Mon 09-07-18 12:01:04, Waiman Long wrote:

quoted

On 07/09/2018 04:19 AM, Michal Hocko wrote:

[...]

quoted

quoted

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percentage has turned out to be a really wrong unit for many tunables
over time. Even 1% can be just too much on really large machines.

Yes, that is true. Do you have any suggestion of what kind of unit
should be used? I can scale down the unit to 0.1% of the system memory.
Alternatively, one unit can be 10k/cpu thread, so a 20-thread system
corresponds to 200k, etc.

I simply think this is a strange user interface. How much is a
reasonable number? How can any admin figure that out?

Without the optional enforcement, the limit is essentially just a
notification mechanism where the system signals that there is something
wrong going on and the system administrator need to take a look. So it
is perfectly OK if the limit is sufficiently high that normally we won't
need to use that many negative dentries. The goal is to prevent negative
dentries from consuming a significant portion of the system memory.

So again. How do you tell the right number?

I am going to reduce the granularity of each unit to 1/1000 of the total
system memory so that for large system with TB of memory, a smaller
amount of memory can be specified.

It is just a matter of time for this to be too coarse as well.
-- 
Michal Hocko
SUSE Labs
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