Re: [RFC PATCH] mm: memcg: Do not count memory.low reclaim if it does not happen

[Roman Gushchin <roman.gushchin@linux.dev>]

> On Mar 24, 2022, at 2:52 AM, Michal Koutný <mkoutny@suse.com> wrote:
> 
> On Wed, Mar 23, 2022 at 02:44:24PM -0700, Roman Gushchin <roman.gushchin@linux.dev> wrote:
>> Does it mean that in the following configuration:
>>    `parent .low=50M
>>      ` s1    .low=0M   .current=50M
>>      ` s2  .low=0M   .current=50M
>> there will be no memory.events::low at all? (assuming the recursive thing is on)
> 
> True, no memory.events:low among siblings.
> Number of memory.events:low in the parent depends on how much has to be
> reclaimed (>50M means carving into parent's protection, hence it'll be
> counted).

Ok, so it’s not really about the implementation details of the reclaim mechanism (I mean rounding up to the batch size etc), it’s a more generic change: do not generate low events for cgroups not explicitly protected by a non-zero memory.low value.

Idk, I don’t have a strong argument against this change (except that it changes the existing behavior), but I also don’t see why such events are harmful. Do you mind elaborating a bit more?

Thank you!