linux-kernel - Re: [RFC PATCH V2 00/22] Intel(R) Resource Director Technology Cache Pseudo-Locking enabling

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Message-ID: <e0d59d83-14a1-6059-6f0b-da47b3b7de31@oracle.com>
Date:   Wed, 14 Feb 2018 10:12:03 -0800
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Reinette Chatre <reinette.chatre@...el.com>, tglx@...utronix.de,
        fenghua.yu@...el.com, tony.luck@...el.com
Cc:     gavin.hindman@...el.com, vikas.shivappa@...ux.intel.com,
        dave.hansen@...el.com, mingo@...hat.com, hpa@...or.com,
        x86@...nel.org, linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>,
        Vlastimil Babka <vbabka@...e.cz>
Subject: Re: [RFC PATCH V2 00/22] Intel(R) Resource Director Technology Cache
 Pseudo-Locking enabling

On 02/13/2018 07:46 AM, Reinette Chatre wrote:
> Adding MM maintainers to v2 to share the new MM change (patch 21/22) that
> enables large contiguous regions that was created to support large Cache
> Pseudo-Locked regions (patch 22/22). This week MM team received another
> proposal to support large contiguous allocations ("[RFC PATCH 0/3]
> Interface for higher order contiguous allocations" at
> http://lkml.kernel.org/r/20180212222056.9735-1-mike.kravetz@oracle.com).
> I have not yet tested with this new proposal but it does seem appropriate
> and I should be able to rework patch 22 from this series on top of that if
> it is accepted instead of what I have in patch 21 of this series.
> 

Well, I certainly would prefer the adoption and use of a more general
purpose interface rather than exposing alloc_gigantic_page().

Both the interface I suggested and alloc_gigantic_page end up calling
alloc_contig_range().  I have not looked at your entire patch series, but
do be aware that in its present form alloc_contig_range will run into
issues if called by two threads simultaneously for the same page range.
Calling alloc_gigantic_page without some form of synchronization will
expose this issue.  Currently this is handled by hugetlb_lock for all
users of alloc_gigantic_page.  If you simply expose alloc_gigantic_page
without any type of synchronization, you may run into issues.  The first
patch in my RFC "mm: make start_isolate_page_range() fail if already
isolated" should handle this situation IF we decide to expose
alloc_gigantic_page (which I do not suggest).

-- 
Mike Kravetz