linux-kernel - Re: [memcg] 0f12156dff: will-it-scale.per_process

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Date:   Tue, 7 Sep 2021 07:20:58 -1000
From:   Tejun Heo <tj@...nel.org>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     Roman Gushchin <guro@...com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        kernel test robot <oliver.sang@...el.com>,
        Vasily Averin <vvs@...tuozzo.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Andrei Vagin <avagin@...il.com>,
        Borislav Petkov <bp@...en8.de>, Borislav Petkov <bp@...e.de>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Dmitry Safonov <0x7f454c46@...il.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        "J. Bruce Fields" <bfields@...ldses.org>,
        Jeff Layton <jlayton@...nel.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Kirill Tkhai <ktkhai@...tuozzo.com>,
        Michal Hocko <mhocko@...nel.org>,
        Oleg Nesterov <oleg@...hat.com>,
        Serge Hallyn <serge@...lyn.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Yutian Yang <nglaive@...il.com>,
        Zefan Li <lizefan.x@...edance.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>, lkp@...ts.01.org,
        kernel test robot <lkp@...el.com>,
        "Huang, Ying" <ying.huang@...el.com>,
        Feng Tang <feng.tang@...el.com>,
        Zhengjun Xing <zhengjun.xing@...ux.intel.com>
Subject: Re: [memcg] 0f12156dff: will-it-scale.per_process_ops -33.6%
 regression

On Tue, Sep 07, 2021 at 11:18:21AM -0600, Jens Axboe wrote:
> 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.

Yeah, it'd need some heuristics to guard against the cache exploding and a
lot of laziness in expiration logic but none of those should be too
complicated.

Thanks.

-- 
tejun