linux-kernel - Re: [PATCH 00/46] Based on latest mm-unstable (85b44c25cd1e).

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Message-ID: <Y7xwoZq+WqCsyXpw@monkey>
Date:   Mon, 9 Jan 2023 11:53:05 -0800
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     James Houghton <jthoughton@...gle.com>,
        Muchun Song <songmuchun@...edance.com>,
        Peter Xu <peterx@...hat.com>,
        David Rientjes <rientjes@...gle.com>,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        Mina Almasry <almasrymina@...gle.com>,
        Zach O'Keefe <zokeefe@...gle.com>,
        Manish Mishra <manish.mishra@...anix.com>,
        Naoya Horiguchi <naoya.horiguchi@....com>,
        "Dr . David Alan Gilbert" <dgilbert@...hat.com>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Baolin Wang <baolin.wang@...ux.alibaba.com>,
        Miaohe Lin <linmiaohe@...wei.com>,
        Yang Shi <shy828301@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 00/46] Based on latest mm-unstable (85b44c25cd1e).

On 01/05/23 11:47, David Hildenbrand wrote:
> On 05.01.23 11:17, James Houghton wrote:
> > This series introduces the concept of HugeTLB high-granularity mapping
> > (HGM). This series teaches HugeTLB how to map HugeTLB pages at
> > high-granularity, similar to how THPs can be PTE-mapped.
> > 
> > Support for HGM in this series is for MAP_SHARED VMAs on x86 only. Other
> > architectures and (some) support for MAP_PRIVATE will come later.
> 
> Why even care about the complexity of COW-sharable anon pages? TBH, I'd just
> limit this to MAP_SHARED and call it a day. Sure, we can come up with use
> cases for everything (snapshotting VMs using fork while also support
> optimized postcopy), but I think this would need some real justification for
> the added complexity and possible (likely!) issues.

I believe the primary use case driving this beyond MAP_SHARED would be
poisoning due to memory errors.  Extending HGM seems to be the most
elegant way to start providing better support for this.  
-- 
Mike Kravetz