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b=Px0z7sfdQLWiFeeGeuiGfraKia/ALAVkdoC6cZGvsboSC7PDRrVvINt+qrvlE/Y5K 07KQWxsxUHJz4wVUtIKbNSC8S31uWkYadOZGecrSulQKq784W6DyBQ+aPGdig/5jXH O8EUkdD1t7FsAsXAnRt57lmSyOgTFi8+0ubHAqX+IkhbQvb6OHbd06JpPopa9w9u+x 58qysMsfszh2cvS5Sjm2RMGUOHHlIobXo3t+DHLYEyKhydIoEQxkbXCpxUDhdYaB/D hKtbSon5A7qgK5lvI/vZbUzU8/2MakRf1r/sJn7pP4On+5GbeH8+5X4+H5nyH5Ul/h DtcsL84/b2ccQ== Message-ID: <352e1f42-2e89-4445-a20e-572ee35c7a0c@kernel.org> Date: Wed, 5 Aug 2026 11:09:52 +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 To: "Vlastimil Babka (SUSE)" , William Roche , 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> <168ad406-f6b5-4623-adac-9f894e410e48@kernel.org> <8f787434-5326-4a8f-92d0-467e817a23b4@kernel.org> <8e48c288-2183-4d58-b69d-5f78344b5da5@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: 112C618000C X-Stat-Signature: sriwbih5phpjcmm8s8syyeh9fu1d1c9f X-HE-Tag: 1785921002-332869 X-HE-Meta: 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 XbItIKU3 njI6kIYEX2uOaOI+9ZVdfZiGFNtOYckikedistjXVYO8VQ7GB9hF0rTbda0fkmKM+gTeOc8+meTAQ2DkFP9zcN6Hb1Azo2q8eFAczNK95be4lTqlhinabMxa3ubMB9MUUcXqddgYLIWwgY4ZXWO5JRSce3uiEg/tgZNn/dwrMA9mua3QlH5+cRZ3CnAI2SwKK5TcQ0jPgpFH0As1lNNs/Bt40JoNkJ8pDltSdxY7SSBcbJu9zfGlIrWYlx9tvgsFOGQIoDJvHDPNp14ye9U9mTyV+SftICUsW6TYS40AubuQs6fqsdOmjvo0htlnhSORUt5TJNkcFvFlViiATui+l25Jg+bqrIRvHJMjBq8Idd5VnOQH+QT8aZWHc6AXXBC8UzwrFMXEA+n+eM1KVvTalhuwEAuqWfHuLHlYwtp02DAK4VGA= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 8/5/26 10:58, Vlastimil Babka (SUSE) wrote: > On 8/4/26 21:51, David Hildenbrand (Arm) wrote: >> On 7/28/26 19:18, Vlastimil Babka (SUSE) wrote: >>> >>> We check all kinds of unexpected state, when that's enable. PageHWPoison >>> could have been considered unexpected too, when the checks were made more >>> and more optional (first by Mel and then me). >>> >>> But indeed it seems the PageHWPoison check is supposed to be load-bearing >>> (hi, Lorenzo!). It's intentionally handled before bad_page() (with a taint) >>> in check_new_page_bad(). Commits 2a7684a23e9c and f4c18e6f7b5b are also a hint. >>> >>> >>> Yes, the PageHWPoison handling was made part of debugging sanity check and >>> then not recognized properly as load-bearing later. >> >> BTW, I'd assume we can check for PageHWPoison at free time fairly efficiently, as we >> touch all page flags already. >> >> Something along the lines of: >> >> diff --git a/mm/page_alloc.c b/mm/page_alloc.c >> index 520ebd2fa40b5..57f89f8684168 100644 >> --- a/mm/page_alloc.c >> +++ b/mm/page_alloc.c >> @@ -1321,6 +1321,7 @@ static __always_inline bool __free_pages_prepare(struct page *page, >> bool init = want_init_on_free(); >> bool compound = PageCompound(page); >> struct folio *folio = page_folio(page); >> + unsigned int hwpoisoned = 0; >> >> if (fpi_flags & FPI_PREPARED) >> return true; >> @@ -1347,21 +1348,6 @@ static __always_inline bool __free_pages_prepare(struct page *page, >> count_vm_events(UNEVICTABLE_PGCLEARED, nr_pages); >> } >> >> - if (unlikely(PageHWPoison(page)) && !order) { >> - /* Do not let hwpoison pages hit pcplists/buddy */ >> - reset_page_owner(page, order); >> - page_table_check_free(page, order); >> - pgalloc_tag_sub(page, 1 << order); >> - >> - /* >> - * The page is isolated and accounted for. >> - * Mark the codetag as empty to avoid accounting error >> - * when the page is freed by unpoison_memory(). >> - */ >> - clear_page_tag_ref(page); >> - return false; >> - } >> - >> VM_BUG_ON_PAGE(compound && compound_order(page) != order, page); >> >> /* >> @@ -1395,8 +1381,26 @@ static __always_inline bool __free_pages_prepare(struct page *page, >> } >> } >> tail_page->flags.f &= ~PAGE_FLAGS_CHECK_AT_PREP; >> + hwpoisoned += PageHWPoison(tail_page); >> } >> } >> + hwpoisoned += PageHWPoison(page); >> + >> + if (unlikely(hwpoisoned)) { >> + /* Do not let hwpoison pages hit pcplists/buddy */ >> + reset_page_owner(page, order); >> + page_table_check_free(page, order); >> + pgalloc_tag_sub(page, 1 << order); >> + >> + /* >> + * The page is isolated and accounted for. >> + * Mark the codetag as empty to avoid accounting error >> + * when the page is freed by unpoison_memory(). >> + */ >> + clear_page_tag_ref(page); >> + return false; >> + } >> + >> if (folio_test_anon(folio)) { >> mod_mthp_stat(order, MTHP_STAT_NR_ANON, -1); >> folio->mapping = NULL; >> diff --git a/tools/testing/selftests/mm/Makefile b/tools/testing/selftests/mm/Makefile >> >> >> Of course, we could also fallback for order>0 to do some smart splitting. > > I think the freeing part is relatively fine, as tackled by this series. I think we should really do something like the above to detect hwpoison, to then fallback to a slow path. > >> Checking on allocation efficiently is indeed a bit more tricky. For compound >> pages prep_compound_page() will already walk all pages. > > Yeah and non-compound high-order pages should just go away eventually, so I > wouldn't worry about making them slower now. > But it's tricky because prep_compound_page() happens later when we don't > expect anything to fail anymore, so it would take some refactoring. Agreed. > >> Having hwpoison logic to just sync with the buddy when setting hwpoison flags >> would be nicer. > > I suggested that (soft-offline does it). There might be some downsides, but > I can't judge how much they would manifest in practice: > > https://lore.kernel.org/all/CACw3F50nVECJ%2Bk4g%3DQVZ80yzi_awCOcUiCuB0CYcUfxND9-7Tw@mail.gmail.com/ Agreed. -- Cheers, David