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b=ekCZ/Dpxd4UXfjUpPJgFSz+5Qae1qUCR1vSSZ8gxKyDdMCl1jyddCKLqopYldDgj1 USDujZCPTeZhGiUDptREnXMGr1shGrif+fIvQoFMpJPidLd5R0DqS1zOJ8nfFMTYG+ dq0GuoMp4dgKLR79+EmQaRwvZYATQHJErH887908uZwyhKnvAuQCgqkGUxWfWj0IBZ 8b/cXJGID70KBufVBtlnM+b92J7fia77hD7wYjjK7NnliafUE2G9fUSvta2wgzDtCy rtF9JdpAYG3E3YmJgIBrGXTkEcL+BGrBC4VVjbPfe+XYn72fBHsz+zzKdL9i0VrM3R mRT19O4etE54A== Message-ID: <7a23511f-365f-436f-b934-6a520510409c@kernel.org> Date: Wed, 23 Sep 2026 13:40:24 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v9 08/15] hugetlb: Use the has_hwpoisoned flag To: Matthew Wilcox Cc: Andrew Morton , Jane Chu , linux-mm@kvack.org, Muchun Song , Oscar Salvador , Miaohe Lin , Naoya Horiguchi , Jan Kara , linux-fsdevel@vger.kernel.org, Christian Brauner , Jiaqi Yan , "Gregory Price (Meta)" References: <20260805210557.1118966-1-willy@infradead.org> <20260805210557.1118966-9-willy@infradead.org> <7608c80e-645b-4d07-bba3-ef45ee36fba4@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: B430516000D X-Stat-Signature: tc18oug35fdd3fwnstkq9117nqjgjsrt X-HE-Tag: 1790163631-869376 X-HE-Meta: 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 iBpPBznA WyVwnhDAESAPEWOxCJ29gmZdq4QGZv3BD5Rzndgcx9q2QUaFlTwGqMvj4feVzBKDKx5D7zdHR1/8vVGh7YTivwVF/22uX0LYO4iTF1ol4fBuxjX57R1/AhXln9Qzu3YbOx4HfdN+w/p9jUdgHaX7nAMVeo8Dgt34xCV2KXhFqXtf+Gt63kTQ0+w9mM+/oGF3Ioi/ciq1nOChvr5DXkrT8NfxkiR5/YvYKS7hs3/PPKlS6oNnU8SqqKiRPPNQszV/OHaOEVtSsbs70D5XE/ulXcDfiP+RQd9KdPuMtSzd+f3ltMwbWambMIzHN3pgoOqeBEOVWY2znP0xr0+l6C6USBnLSHZhX6+vbRa6oHHWJIe0mL0FH+eLEZYQVcE0Qr7gcGN1B Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 9/21/26 23:32, Matthew Wilcox wrote: > On Fri, Sep 18, 2026 at 03:44:12PM +0200, David Hildenbrand (Arm) wrote: >> I'm a terrible person and it took me way too long to get back to this :( >> >>> >>> You make it sound so easy ;-) >> >> Heh, as long as you hold a folio reference it really is :) >> >>> >>> If we don't hold a reference on the folio, then the folio (whether it's >>> hugetlb or not) can be split. And then folio_test_hwpoison() can hit >>> the assertion that it's now a tail page. >> >> Right. I am/was missing the connection to "generic_file_read_iter() in hugetlbfs". > > We might be able to split this into two series at this point. That would be good, because I suspect the "generic_file_read_iter() in hugetlbfs" part is less controversial than the hugetlb cleanup and we can just merge that easily without touching too much other code. [...] >>> If we could get rid of HVO, we could do it entirely on struct page. >> >> That's what I hope we will achieve at some point. > > I'm not sure that's a realistic hope in the next few years. :( > Even if > we get struct page down to 8 bytes, that's 2MB of memory per 1GiB allocation > (assuming 4KiB pages). Always a tempting target for someone looking for > memory savings. Ack > > I would prefer an out-of-line tree that doesn't rely on a bit in struct > page. Maybe a bit in struct folio wuld be fine (which tells you whether > it's OK to skip the tree search). Yes, that would likely be better. A single bit would likely just remove any overhead of checking in the common case (no hwpoison). Not sure what to do with non-folio things. > >>> Or, as above, entirely rearchitecture hwpoison handling to not be based >>> around pages or folios any more. >>> >>> >>> Blame Sashiko! I'm going to ignore it in future, but it's really good >>> at nerd-sniping "hey all of this is already broken and you could fix it >>> as part of this series". >> >> Right, and this is only the tip of the iceberg, because the entire hwpoison >> infrastructure is a complete hacked-on racy piece of ... engineering excellence. >> >> To summarize my question: is it possible to separate for this series the >> pagecache part (Use generic_file_read_iter() in hugetlbfs) from all the hugetlb >> hwpoison rework? >> >> OTOH, if it's really not avoidable, please let me know. > > I think Sashiko will whine and complain incessantly if we drop the > race elimination patches off the front. I can try it, but is it worth > doing? Note that Sashiko will apparently no longer complain about preexisting stuff. I've been told that these reports are now collected elsewhere. So I wouldn't worry about Sashiko crying about hwpoison stuff that was broken for ever. I'd rather have fixes for that handled separately (after we properly discuss a better long-term solution to handle most these races and where to store hwpoison information long-term). -- Cheers, David