linux-kernel - Re: [PATCH v5 3/9] mm/swap: Split swap cache into 64MB trunks

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Message-ID: <20170112164717.GA26499@linux.intel.com>
Date:   Thu, 12 Jan 2017 08:47:18 -0800
From:   Tim Chen <tim.c.chen@...ux.intel.com>
To:     Andi Kleen <ak@...ux.intel.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        "Huang, Ying" <ying.huang@...el.com>, dave.hansen@...el.com,
        aaron.lu@...el.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Hugh Dickins <hughd@...gle.com>,
        Shaohua Li <shli@...nel.org>, Minchan Kim <minchan@...nel.org>,
        Rik van Riel <riel@...hat.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Hillf Danton <hillf.zj@...baba-inc.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Jonathan Corbet <corbet@....net>
Subject: Re: [PATCH v5 3/9] mm/swap: Split swap cache into 64MB trunks

On Wed, Jan 11, 2017 at 03:19:37PM -0800, Andi Kleen wrote:
> > Switching from a single radix-tree to an array of radix-trees to reduce
> > contention seems a bit hacky.  That we can do this and have everything
> > continue to work tells me that we're simply using an inappropriate data
> > structure to hold this info.
> 
> What would you use instead?

I agree that this approach is a bit hacky.  However, it is pretty
effective and simple.  If later on we come up with a better solution to
scale modfication of the radix tree, we can collapse the radix trees.

I think developing a scalable radix tree with write modifications will
take quite a while and is a non-trivial effort. With almost memory speed
SSDs coming on the market soon, I think having a workable solution now
and optimizing it for long term is reasonabale.

Tim


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