Re: [PATCH] mm/damon/core: accumulate applied size to quota->charged_sz

[SeongJae Park <sj@kernel.org>]

On Fri, 29 Nov 2024 17:31:01 +0900 Honggyu Kim <honggyu.kim@sk.com> wrote:

> While testing DAMOS_MIGRATE_COLD action, Yunjeong found that the
> quota->charged_sz is way less than actually migrated size.

You mean "more", not "less", right?

And, is it a problem for your use case?  Could you please share more details?

> 
> In damos_apply_scheme(), quota->charged_sz is used when checking whether
> the quota exceeds the effective size.  The current implementation
> accumulates the charged_sz with sz(region size), but many pages in the
> region might be discarded by DAMOS filters.
> 
> In order to make the quota calculation more accurate, charged_sz is
> better to be accumulated by the actually applied size, which is
> sz_applied in the code.

This is an intended behavior.  Quota is for making a limit of resource
consumption from DAMOS.  Trying a DAMOS action consumes some of the system
resource even if it was eventually filtered out or failed, so we charge those.

We can consider changes of the behaior depending on problems and use cases, but
it is unclear to me.  Could you please elaborate, as I requested above?


Thanks,
SJ

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