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Date:   Wed, 14 Apr 2021 15:36:26 +0100
From:   Matthew Wilcox <willy@infradead.org>
To:     Yu Zhao <yuzhao@google.com>
Cc:     linux-mm@kvack.org, Alex Shi <alexs@kernel.org>,
        Andi Kleen <ak@linux.intel.com>,
        Andrew Morton <akpm@linux-foundation.org>,
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        Hillf Danton <hdanton@sina.com>, Jens Axboe <axboe@kernel.dk>,
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        Jonathan Corbet <corbet@lwn.net>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
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        Miaohe Lin <linmiaohe@huawei.com>,
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        Yang Shi <shy828301@gmail.com>,
        Ying Huang <ying.huang@intel.com>, Zi Yan <ziy@nvidia.com>,
        linux-kernel@vger.kernel.org, lkp@lists.01.org,
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Subject: Re: [PATCH v2 10/16] mm: multigenerational lru: mm_struct list
Message-ID: <20210414143626.GT2531743@casper.infradead.org>
References: <20210413065633.2782273-1-yuzhao@google.com>
 <20210413065633.2782273-11-yuzhao@google.com>
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On Tue, Apr 13, 2021 at 12:56:27AM -0600, Yu Zhao wrote:
> In order to scan page tables, we add an infrastructure to maintain
> either a system-wide mm_struct list or per-memcg mm_struct lists.
> Multiple threads can concurrently work on the same mm_struct list, and
> each of them will be given a different mm_struct.
> 
> This infrastructure also tracks whether an mm_struct is being used on
> any CPUs or has been used since the last time a worker looked at it.
> In other words, workers will not be given an mm_struct that belongs to
> a process that has been sleeping.

This seems like a great use for an allocating XArray.  You can use a
search mark to indicate whether it's been used since the last time a
worker looked at it.