linux-kernel - Re: [PATCH v1 14/14] mm: multigenerational lru: documentation

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Date:   Mon, 22 Mar 2021 00:09:56 -0600
From:   Yu Zhao <yuzhao@...gle.com>
To:     Alex Shi <alex.shi@...ux.alibaba.com>
Cc:     linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Hillf Danton <hdanton@...a.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Matthew Wilcox <willy@...radead.org>,
        Mel Gorman <mgorman@...e.de>, Michal Hocko <mhocko@...e.com>,
        Roman Gushchin <guro@...com>, Vlastimil Babka <vbabka@...e.cz>,
        Wei Yang <richard.weiyang@...ux.alibaba.com>,
        Yang Shi <shy828301@...il.com>,
        Ying Huang <ying.huang@...el.com>,
        linux-kernel@...r.kernel.org, page-reclaim@...gle.com
Subject: Re: [PATCH v1 14/14] mm: multigenerational lru: documentation

On Fri, Mar 19, 2021 at 05:31:20PM +0800, Alex Shi wrote:
> 
> 
> 在 2021/3/13 下午3:57, Yu Zhao 写道:
> > +Recipes
> > +-------
> > +:Android on ARMv8.1+: ``X=4``, ``N=0``
> > +
> > +:Android on pre-ARMv8.1 CPUs: Not recommended due to the lack of
> > + ``ARM64_HW_AFDBM``
> > +
> > +:Laptops running Chrome on x86_64: ``X=7``, ``N=2``
> > +
> > +:Working set estimation: Write ``+ memcg_id node_id gen [swappiness]``
> > + to ``/sys/kernel/debug/lru_gen`` to account referenced pages to
> > + generation ``max_gen`` and create the next generation ``max_gen+1``.
> > + ``gen`` must be equal to ``max_gen`` in order to avoid races. A swap
> > + file and a non-zero swappiness value are required to scan anon pages.
> > + If swapping is not desired, set ``vm.swappiness`` to ``0`` and
> > + overwrite it with a non-zero ``swappiness``.
> > +
> > +:Proactive reclaim: Write ``- memcg_id node_id gen [swappiness]
> > + [nr_to_reclaim]`` to ``/sys/kernel/debug/lru_gen`` to evict
> > + generations less than or equal to ``gen``. ``gen`` must be less than
> > + ``max_gen-1`` as ``max_gen`` and ``max_gen-1`` are active generations
> > + and therefore protected from the eviction. ``nr_to_reclaim`` can be
> > + used to limit the number of pages to be evicted. Multiple command
> > + lines are supported, so does concatenation with delimiters ``,`` and
> > + ``;``.
> > +
> 
> These are difficult options for users, especially for 'races' involving.
> Is it possible to simplify them for end users?

They look simple for a few lruvecs, but do become human-unfriendly on
servers that have thousands of lruvecs.

It's certainly possible simplify them, but we'd have to sacrifice
some flexibility. Any particular idea in mind?