linux-kernel - Re: [PATCH 0/1] memory offline issues with hugepage size

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Message-ID: <57E2D124.9000108@linux.intel.com>
Date:   Wed, 21 Sep 2016 11:27:48 -0700
From:   Dave Hansen <dave.hansen@...ux.intel.com>
To:     Michal Hocko <mhocko@...nel.org>,
        Mike Kravetz <mike.kravetz@...cle.com>
Cc:     Gerald Schaefer <gerald.schaefer@...ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        "Aneesh Kumar K . V" <aneesh.kumar@...ux.vnet.ibm.com>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Rui Teng <rui.teng@...ux.vnet.ibm.com>
Subject: Re: [PATCH 0/1] memory offline issues with hugepage size > memory
 block size

On 09/21/2016 11:20 AM, Michal Hocko wrote:
> I would even question the per page block offlining itself. Why would
> anybody want to offline few blocks rather than the whole node? What is
> the usecase here?

The original reason was so that you could remove a DIMM or a riser card
full of DIMMs, which are certainly a subset of a node.

With virtual machines, perhaps you only want to make a small adjustment
to the memory that a VM has.  Or, perhaps the VM only _has_ one node.
Granted, ballooning takes care of a lot of these cases, but memmap[]
starts to get annoying at some point if you balloon too much memory away.