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 11F6A480DF8 for ; Wed, 22 Jul 2026 09:40:36 +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=1784713238; cv=none; b=C5iftwyUUas0UEsT3qvoTOwaID3SEbey5gkVYmfyXIWueK9mSkPgCddlZd+7A4WaWyqTBgWH5dZIRPHBkyXH3VlgAhPB/ZhtYh/xjcjQ47oKUl5l1NEXVITQKTHMIbRfIS14RFH4MjrWwfpy0h+Rx3AtBiPYR3P+kHxfT7S8rRY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784713238; c=relaxed/simple; bh=WUFmKIzJDwpkAK/YMfBxeVVD3Lj/ZYnXyLqY2HkFSTg=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=h7uM5cN+oPTPOFyANllMzIausx7fgtIlI50chKn5H0b2p9mTJUEI+ciULrKTqZGnOH/Y1QlL2mhyBTF03MO1LHpS1JGXXZGZ0D3kJcTyF4O3UOGIiojFMf8mmw1XbumbfSka5uflTohLnlxfDzv01COj7y/QEQlu5kQdfvVoytg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=fjMLOuBg; 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="fjMLOuBg" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 220381F00A3A; Wed, 22 Jul 2026 09:40:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1784713236; bh=m4UMvly8imvHxcIAI3YLVRZx2HuJe9s4Vcuhvbq1FbU=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=fjMLOuBghmOwfyIusYkgjFTMJs3mvTCjCzYEVPr8hvgrRkPYRi3oDdnctkdKj1K3O IyuSaIOydqAodZokUTwyCB05hz9dotCMieLgz9kJJ+UNUT7RrUbNsDpQjXpAfKO9M0 2Ja04BrfO2ZUFY10AoDe8p5L/kGUr7X+DcDHTQhjXBSaf2HG4fvv2gGQ/O9Upazc4X Us/5tC3Tf9ShV/xxK6ENmcqxdiLVNYws4AJMXu9huRRsEOc5cHuDxUixx9/3WSE8HZ 8ZS/wy+kC4JeAYuYzfUbypWIcueESs5N3yCq1X7malNbAetuqUxjY7F581RwC45wTA Bs1tS7nY15WwA== Message-ID: Date: Wed, 22 Jul 2026 11:40:29 +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 2/5] mm/page_alloc: only free healthy pages in high-order has_hwpoisoned folio Content-Language: en-US To: 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, david@kernel.org, william.roche@oracle.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> <20260705180714.3708947-3-jiaqiyan@google.com> From: "Vlastimil Babka (SUSE)" Autocrypt: addr=vbabka@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit 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 it 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. > > Memory failure recovery (MFR) in kernel does attempt to take > raw HWPoison page off buddy allocator after > dissolve_free_hugetlb_folio(). However, there is always a time > window between dissolve_free_hugetlb_folio() frees a HWPoison > high-order folio to buddy allocator and MFR takes HWPoison > raw page off buddy allocator. > > Another similar situation is when a transparent huge page (THP) > runs into memory failure but splitting failed. Such THP will > eventually be released to buddy allocator when owning userspace > processes are gone, but with certain subpages having HWPoison. > > One obvious way to avoid both problems is to add page sanity > checks in page allocate or free path. However, it is against > the past efforts to reduce sanity check overhead [1,2,3]. > > Introduce free_has_hwpoisoned() to only free the healthy pages > and to exclude the HWPoison ones in the high-order folio. > The idea is to iterate through the sub-pages of the folio to > identify contiguous ranges of healthy pages. > > free_has_hwpoisoned() is added at the end of __free_pages_prepare() > as a shortcut and only if PG_has_hwpoisoned indicates HWPoison page > exists and after checks and preparations in __free_pages_prepare() > all succeeded. It then use __free_prepared_contig_range() to > decompose healthy range into the largest possible chunks of > different orders, then freed via __free_frozen_pages(). > > free_has_hwpoisoned() has linear time complexity wrt the number > of pages in the folio. While the power-of-two decomposition > ensures that the number of calls to the buddy allocator is > logarithmic for each contiguous healthy range, the mandatory > linear scan of pages to identify PageHWPoison() defines the > overall time complexity. For a 1G hugepage having 8 HWPoison > pages, free_has_hwpoisoned() takes around 1ms on average on > a system having 56 Intel Skylake physical cores. This is > 15x to the case of freeing no HWPoison page. The cost is far > from triggering soft lockup, and fair for handling exceptional > hardware memory errors. > > [1] https://lore.kernel.org/linux-mm/1460711275-1130-15-git-send-email-mgorman@techsingularity.net > [2] https://lore.kernel.org/linux-mm/1460711275-1130-16-git-send-email-mgorman@techsingularity.net > [3] https://lore.kernel.org/all/20230216095131.17336-1-vbabka@suse.cz > > Signed-off-by: Jiaqi Yan Reviewed-by: Vlastimil Babka (SUSE) One thing below: > @@ -6956,6 +7016,61 @@ void __free_contig_range(unsigned long pfn, unsigned long nr_pages) > __free_contig_range_common(pfn, nr_pages, /* is_frozen= */ false); > } > > +/* > + * Given some contiguous pages that have certain number of HWPoison page(s), > + * free only the healthy ones. > + * > + * Used at the end of __free_pages_prepare(). Even if having HWPoison pages, > + * breaking down compound page and clearing metadata (e.g. page owner, alloc > + * tag) can be done together during __free_pages_prepare(), which simplifies > + * the splitting here: unlike __split_unmapped_folio(), there is no need to > + * turn split pages into a compound page or to carry metadata. > + * > + * It scans every raw page of the compound page and causes nontrivial overhead. > + * So only use this when the compound page contains HWPoison page(s). > + * > + * It also works when order == 0, regardless of PageHWPoison() or not. > + * > + * This implementation needs rework in memdesc world. > + */ > +static void free_has_hwpoisoned(struct page *page, unsigned int order, > + fpi_t fpi_flags) > +{ > + unsigned long curr = page_to_pfn(page); > + unsigned long end_pfn = curr + (1 << order); > + unsigned long next; > + unsigned long total_freed = 0; > + unsigned long total_hwp = 0; > + > + while (curr < end_pfn) { > + next = curr; > + > + while (next < end_pfn && !PageHWPoison(pfn_to_page(next))) > + ++next; > + > + if (next != end_pfn) { > + /* > + * Avoid accounting error when the page is freed > + * by unpoison_memory(). > + */ > + clear_page_tag_ref(pfn_to_page(next)); > + ++total_hwp; > + } > + > + __free_prepared_contig_range(pfn_to_page(curr), next - curr, > + fpi_flags); > + total_freed += next - curr; > + > + if (next == end_pfn) > + break; > + > + curr = next + 1; > + } > + > + pr_info("Freed %#lx pages, excluded %#lx HWPoison pages\n", > + total_freed, total_hwp); Should we really print this? Maybe just pr_debug() or not at all? > +} > + > #ifdef CONFIG_CONTIG_ALLOC > /* Usage: See admin-guide/dynamic-debug-howto.rst */ > static void alloc_contig_dump_pages(struct list_head *page_list)