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b=OMUG6G9A0CrJ+g1RwqaNvBOi+c/wGmv5p1KyqABj0ZIa+CcdOwaylhu8HktFF5RSs rRs8k0zSh0MFh8jxE+BdFB3RYNgagb3VwPRuTING5/alWIKHIrTjm8f/XEQoYkGTU5 67ZQ+9o2bdnQnmBZgTlRva1JzxjgXF20KZHEuWAHektU29YK4UokYQrPQ1odGE9zdP fzSvK3+4xdSlikz+lmnSw6L1qntgHR9SXi2EDMLcroaZn7w0T8igoH216ZsRdiwUuB lurDu5dPVLBt+EQTaxgRCXCPomVLoNn5sWJU3dgK1Mkakmjq9hz+BIOxKKRIIls7CW 3ag/bvRjhDbbA== Message-ID: Date: Wed, 22 Jul 2026 11:03:12 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v6 0/5] Only free healthy pages in high-order has_hwpoisoned folio Content-Language: en-US From: "Vlastimil Babka (SUSE)" To: William Roche , "David Hildenbrand (Arm)" , Jiaqi Yan , linmiaohe@huawei.com, ljs@kernel.org, ziy@nvidia.com Cc: osalvador@kernel.org, harry.yoo@oracle.com, willy@infradead.org, osalvador@suse.de, jackmanb@google.com, hannes@cmpxchg.org, nao.horiguchi@gmail.com, tony.luck@intel.com, wangkefeng.wang@huawei.com, jane.chu@oracle.com, akpm@linux-foundation.org, muchun.song@linux.dev, liam@infradead.org, rientjes@google.com, duenwen@google.com, jthoughton@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, rppt@kernel.org, shuah@kernel.org, surenb@google.com, mhocko@suse.com, boudewijn@delta-utec.com References: <20260705180714.3708947-1-jiaqiyan@google.com> <85cb7ea8-8116-4092-8310-69b61eb8602c@kernel.org> <1dea7b3c-7740-474d-b9d4-cd2baf47f181@kernel.org> Autocrypt: addr=vbabka@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: DF8591A000B X-Stat-Signature: 1mhfmpg9g4qo6pngibbdwe7qhzwd9zfb X-HE-Tag: 1784711000-345222 X-HE-Meta: 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 ZqbiDZdV Y3p1u0RSl1ZhP7yKmT/Okp9zUQnQfkme7NHOFDEKZO/C3cRSpqTqDO0uJP3iEwqYE2i2SBhuk/0CxoJ86dJ5pY9/uEFMmfOL2XKxZ22pRzZ6EZObNVn5qvR7fGFsyZ9bVA/e8SDh9XYgZ/CD+iiqy8H8GqppKLPdHpryGDN2z4gfdfCk5vtMHwVq7oUAdSuHv38+MRw/GeBGjkf++ujp3MiyY018xU5OLMMcntSfpOf2BN7l+8uO/XuId+MVrltEXvt5/ImkFMXd687hFHxskohtVyeejIcswWRk8lVtC46e/dYfwkeFt9JVyf1aNi4ZP2kQnBQ9WAjg/t7zrn3Jdw8imJafZ9N77LZvIphEZGZjXm22FCHFbBPg4Rl3Xu9BsabK1mI4OFLsroCCCLNAZcOIgCg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 7/22/26 10:27, Vlastimil Babka (SUSE) wrote: > On 7/17/26 15:06, William Roche wrote: >> On 7/17/26 12:18, David Hildenbrand (Arm) wrote: >>> On 7/5/26 20:07, Jiaqi Yan wrote: >>>> At the end of dissolve_free_hugetlb_folio(), a free HugeTLB >>>> folio becomes non-HugeTLB and is released to buddy allocator >>>> as a high-order folio, e.g. a folio that contains 262144 pages >>>> if the folio was a 1G HugeTLB hugepage. >>>> >>>> This is problematic if the HugeTLB hugepage contained HWPoison >>>> subpages. In that case, since buddy allocator does not check >>>> HWPoison for non-zero-order folio, the raw HWPoison page can >>>> be given out with its buddy page and be re-used by either >>>> kernel or userspace. >>> >>> I still don't like the complexity of this, in particular, as we have different >>> mechanisms in the page allocator already to try handling this, >>> >>> We also do have cases where we set the hwpoison bit, while a page is just about >>> to get allocated from the buddy. So before we take it off the buddy, we might >>> just hand out the page. >>> >>> check_new_pages() seems to check for PageHWPoison() and make us not hand out >>> such pages. It's guarded by "check_pages" but it seems to do exactly what we are >>> looking for, now? >> >> >> Just adding a comment about this aspect: >> The check_new_pages() mechanism used by the __rmqueue functions should >> filter these pages out, but this has been disabled by default in 2023 >> with: >> [PATCH] mm, page_alloc: reduce page alloc/free sanity checks >> https://lore.kernel.org/all/20230216095131.17336-1-vbabka@suse.cz >> >> So it would need to be enabled back, taking some of the performance hit. >> (and I personally think that it has to be done) > > Would it truly fix the issue, or rather there would still be a race window > left where we check that there's no hwpoison flag in the re-enabled check, > and only then someone sets it? > > Also, can the hardware actually detect a problem with a page that nobody > accesses? I guess if yes, it's only in some corner cases. > > So I'm wary about penalizing the allocator paths again. If the page is in > the buddy allocator, shouldn't it be isolated away as part of setting the > hwpoison? I thought we already did that? Looking at the code, seems soft_offline_page() tries to take a refcount first and then sets the hwpoison flag, so it should be completely race-free wrt the page allocator. memory_failure() seems to start with TestSetPageHWPoison() and only then tries to get the refcount. Wonder if it should be that way. > So assuming we don't just leave > hwpoison pages in the buddy and this is only about some small race window > where it's being taken away from the buddy? Then the extra check would only > make a small window smaller, but is it worth it? > >> A note about the related project: >> This patch is an addition to the "mm: memfd/hugetlb: introduce >> memfd-based userspace MFR policy" >> project -- recycling the impacted hugetlb pages. >> >> I do think that "memfd-based userspace MFR policy" is a valuable >> enhancement, and if the impacted large page can be more easily recycled >> enabling check_new_pages() it's even better ! >> >> HTH. >