From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E965F3F7886 for ; Wed, 5 Aug 2026 09:10:02 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785921004; cv=none; b=PbS9613Mkds6C2M77c8lfzvgM6f7aNPaJGfyTRaP06orcD5zMaX4FRG7G3ng6kzTjSZBpXnkB67L/OUnVWjscb+QcpnuOCo05CHNw/3lKYqnDwKa5Nf9cWqDhUqqpAJvD/TwP685WQUYbwoblsCarZOOTQHTbDLNQXmS+wrzR9U= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785921004; c=relaxed/simple; bh=HbRnAZToJykVtS1JmiBRc8A4JXLLKSXfkLwombupz7A=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=uckDTXZ3tIDnt9WU7dGCj5HTMHYIwn3NzPslwF2X5nClacHDXvPxUju+8bfgek3tmWkjNQ6s2dODGCINgH0oO8g9ylpej0RBiSnv2aAhYrD7G0RdP5kTsO8FbQUIfrTPCTnHWGwaTlrV9TW2Re45v7cxGNIO4egm3E04G5U/q80= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Px0z7sfd; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Px0z7sfd" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 09B2C1F000E9; Wed, 5 Aug 2026 09:09:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1785921002; bh=arisYwSnWIrQ0tx47rogqMxiybhAxWfzJtYPr/R4Eb4=; h=Date:Subject:To:Cc:References:From:In-Reply-To; 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 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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 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