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Subject: Re: [PATCH 16/18] mm: memcontrol: charge swapin pages on
 instantiation
To:     Johannes Weiner <hannes@cmpxchg.org>,
        Joonsoo Kim <js1304@gmail.com>
Cc:     Shakeel Butt <shakeelb@google.com>,
        Hugh Dickins <hughd@google.com>,
        Michal Hocko <mhocko@suse.com>,
        "Kirill A. Shutemov" <kirill@shutemov.name>,
        Roman Gushchin <guro@fb.com>, linux-mm@kvack.org,
        cgroups@vger.kernel.org, linux-kernel@vger.kernel.org,
        kernel-team@fb.com
References: <20200420221126.341272-1-hannes@cmpxchg.org>
 <20200420221126.341272-17-hannes@cmpxchg.org>
From:   Alex Shi <alex.shi@linux.alibaba.com>
Message-ID: <6f03ed4e-f917-2ccc-26c0-c438c84d3d97@linux.alibaba.com>
Date:   Tue, 21 Apr 2020 17:21:26 +0800
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?? 2020/4/21 ????6:11, Johannes Weiner д??:
> Right now, users that are otherwise memory controlled can easily
> escape their containment and allocate significant amounts of memory
> that they're not being charged for. That's because swap readahead
> pages are not being charged until somebody actually faults them into
> their page table. This can be exploited with MADV_WILLNEED, which
> triggers arbitrary readahead allocations without charging the pages.
> 
> There are additional problems with the delayed charging of swap pages:
> 
> 1. To implement refault/workingset detection for anonymous pages, we
>    need to have a target LRU available at swapin time, but the LRU is
>    not determinable until the page has been charged.
> 
> 2. To implement per-cgroup LRU locking, we need page->mem_cgroup to be
>    stable when the page is isolated from the LRU; otherwise, the locks
>    change under us. But swapcache gets charged after it's already on
>    the LRU, and even if we cannot isolate it ourselves (since charging
>    is not exactly optional).
> 
> The previous patch ensured we always maintain cgroup ownership records
> for swap pages. This patch moves the swapcache charging point from the
> fault handler to swapin time to fix all of the above problems.
> 
> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>

Reviewed-by: Alex Shi <alex.shi@linux.alibaba.com>