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Subject: Re: [memcg] 0f12156dff: will-it-scale.per_process_ops -33.6%
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To:     Tejun Heo <tj@kernel.org>, Roman Gushchin <guro@fb.com>
Cc:     Linus Torvalds <torvalds@linux-foundation.org>,
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From:   Jens Axboe <axboe@kernel.dk>
Message-ID: <22a0156e-f74f-51c8-b7fd-9b5a375d7c81@kernel.dk>
Date:   Tue, 7 Sep 2021 11:18:21 -0600
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On 9/7/21 11:14 AM, Tejun Heo wrote:
> Hello,
> 
> On Tue, Sep 07, 2021 at 10:11:21AM -0700, Roman Gushchin wrote:
>> There are two polar cases:
>> 1) a big number of relatively short-living allocations, which lifetime is well
>>    bounded (e.g. by a lifetime of a task),
>> 2) a relatively small number of long-living allocations, which lifetime
>>    is potentially indefinite (e.g. struct mount).
>>
>> We can't use the same approach for both cases, otherwise we'll run into either
>> performance or garbage collection problems (which also lead to performance
>> problems, but delayed).
> 
> Wouldn't a front cache which expires after some seconds catch both cases?

A purely time based approach might be problematic, as you can allocate a
LOT of data in a short amount of time. Heuristics probably need to be a
hybrid of "time much time has passed" OR "we're over the front cache
threshold in terms of deferred accounting". But yes, I don't see why
we'd necessarily need different approaches for short vs long life times.

-- 
Jens Axboe