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Message-ID: <4b52c79e-7b40-1d5e-bd92-d99224be8ba0@redhat.com>
Date:   Tue, 10 Jan 2023 16:47:49 +0100
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Subject: Re: [PATCH 00/46] Based on latest mm-unstable (85b44c25cd1e).
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To:     Mike Kravetz <mike.kravetz@oracle.com>
Cc:     James Houghton <jthoughton@google.com>,
        Muchun Song <songmuchun@bytedance.com>,
        Peter Xu <peterx@redhat.com>,
        David Rientjes <rientjes@google.com>,
        Axel Rasmussen <axelrasmussen@google.com>,
        Mina Almasry <almasrymina@google.com>,
        Zach O'Keefe <zokeefe@google.com>,
        Manish Mishra <manish.mishra@nutanix.com>,
        Naoya Horiguchi <naoya.horiguchi@nec.com>,
        "Dr . David Alan Gilbert" <dgilbert@redhat.com>,
        "Matthew Wilcox (Oracle)" <willy@infradead.org>,
        Vlastimil Babka <vbabka@suse.cz>,
        Baolin Wang <baolin.wang@linux.alibaba.com>,
        Miaohe Lin <linmiaohe@huawei.com>,
        Yang Shi <shy828301@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
References: <20230105101844.1893104-1-jthoughton@google.com>
 <60f06008-dea5-a08e-edec-fc4aec76dfb5@redhat.com> <Y7xwoZq+WqCsyXpw@monkey>
From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat
In-Reply-To: <Y7xwoZq+WqCsyXpw@monkey>
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On 09.01.23 20:53, Mike Kravetz wrote:
> 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.

Good point. Although I wonder if in practice, most applicable users 
either already are, or should switch to, using MAP_SHARED hugetlb.

-- 
Thanks,

David / dhildenb