linux-kernel - Re: [RFC V2 02/12] mm: Isolate HugeTLB allocations away from CDM nodes

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Message-Id: <be8665a1-43d2-436a-90df-b644365a2fc5@linux.vnet.ibm.com>
Date:   Tue, 31 Jan 2017 06:33:12 +0530
From:   Anshuman Khandual <khandual@...ux.vnet.ibm.com>
To:     Dave Hansen <dave.hansen@...el.com>,
        Anshuman Khandual <khandual@...ux.vnet.ibm.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Cc:     mhocko@...e.com, vbabka@...e.cz, mgorman@...e.de,
        minchan@...nel.org, aneesh.kumar@...ux.vnet.ibm.com,
        bsingharora@...il.com, srikar@...ux.vnet.ibm.com,
        haren@...ux.vnet.ibm.com, jglisse@...hat.com,
        dan.j.williams@...el.com
Subject: Re: [RFC V2 02/12] mm: Isolate HugeTLB allocations away from CDM
 nodes

On 01/30/2017 10:49 PM, Dave Hansen wrote:
> On 01/29/2017 07:35 PM, Anshuman Khandual wrote:
>> HugeTLB allocation/release/accounting currently spans across all the nodes
>> under N_MEMORY node mask. Coherent memory nodes should not be part of these
>> allocations. So use system_ram() call to fetch system RAM only nodes on the
>> platform which can then be used for HugeTLB allocation purpose instead of
>> N_MEMORY node mask. This isolates coherent device memory nodes from HugeTLB
>> allocations.
> 
> Does this end up making it impossible to use hugetlbfs to access device
> memory?

Right, thats the implementation at the moment. But going forward if we need
to have HugeTLB pages on the CDM node, then we can implement through the
sysfs interface from individual NUMA node paths instead of changing the
generic HugeTLB path. I wrote this up in the cover letter but should also
have mentioned in the comment section of this patch as well. Does this
approach look okay ?

"Now, we ensure complete HugeTLB allocation isolation from CDM nodes. Going
forward if we need to support HugeTLB allocation on CDM nodes on targeted
basis, then we would have to enable those allocations through the
/sys/devices/system/node/nodeN/hugepages/hugepages-16384kB/nr_hugepages
interface while still ensuring isolation from other generic sysctl and
/sys/kernel/mm/hugepages/hugepages-16384kB/nr_hugepages interfaces."