From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from canpmsgout03.his.huawei.com (canpmsgout03.his.huawei.com [113.46.200.218]) (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 751F127B35B for ; Tue, 9 Jun 2026 03:44:57 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=113.46.200.218 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780976701; cv=none; b=ElhDwV/w5rdUxmX0nu6k8jrexAuaJhcy/yUM/40uFqi+QVRCMCCzTR44cFzvOOe9XlJpf/GIxdMzUlAD7ei2XYNIZ11LCmClIuOE5LSRQ7W3Q7/r7gkhn5lU+GNVt+iNUzYGFj1eHGRAbKSj+6McAp+WLzoIiNi7tikqkog8840= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780976701; c=relaxed/simple; bh=+syUM6jzoEgldl9hB36kSEK8hrRtMt0X75cB/oia6NY=; h=Subject:To:CC:References:From:Message-ID:Date:MIME-Version: In-Reply-To:Content-Type; b=HXAxPfibYCtMsMAYu8YahmUSEvxS2v/Pmpbt6Efxgqrr5cwuzUO2nsVMfX6a3rODzXuQtiE6yHNx9135zJWJqmCnM/fc/29rkTr1Uqm4K4HmvblyRq8ezHXcBfReq4kctS6UsdaVwv6nmjDxRkZfYmQmCq13dyzk2d/5R7evmo4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com; spf=pass smtp.mailfrom=huawei.com; dkim=pass (1024-bit key) header.d=huawei.com header.i=@huawei.com header.b=GqlAwjbC; arc=none smtp.client-ip=113.46.200.218 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=huawei.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=huawei.com header.i=@huawei.com header.b="GqlAwjbC" dkim-signature: v=1; a=rsa-sha256; d=huawei.com; s=dkim; c=relaxed/relaxed; q=dns/txt; h=From; bh=cJEBHfzpdSI7jJEj6r2mkE4T7/MNZZCxJ7D6F6LoI5Y=; b=GqlAwjbCyhW4RI4yEiZPHwk/dY5roBbGJrKi9EArE6LHLMvAsS7RauBNLsVr9E3p499erBOPl jeQdzcPN4HPQm9UdJWeiUnbMnsgi6YfBFzLjfW1V5mxjFf1UhmAxtorymZ4IgRxS823qinTE0K6 0pnZ+K7Ms9zr+S1HW6B7kUQ= Received: from mail.maildlp.com (unknown [172.19.162.140]) by canpmsgout03.his.huawei.com (SkyGuard) with ESMTPS id 4gZF2n6hb5zpStk; Tue, 9 Jun 2026 11:37:05 +0800 (CST) Received: from dggemv705-chm.china.huawei.com (unknown [10.3.19.32]) by mail.maildlp.com (Postfix) with ESMTPS id 885E7203B8; Tue, 9 Jun 2026 11:44:54 +0800 (CST) Received: from kwepemq500010.china.huawei.com (7.202.194.235) by dggemv705-chm.china.huawei.com (10.3.19.32) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1544.11; Tue, 9 Jun 2026 11:44:54 +0800 Received: from [10.173.124.160] (10.173.124.160) by kwepemq500010.china.huawei.com (7.202.194.235) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1544.11; Tue, 9 Jun 2026 11:44:52 +0800 Subject: Re: [PATCH v5 1/4] mm/page_alloc: only free healthy pages in high-order has_hwpoisoned folio To: Jiaqi Yan CC: , , , , , , , , , , , , , , , , , , , , , , , , , , , , References: <20260531055829.3636554-1-jiaqiyan@google.com> <20260531055829.3636554-2-jiaqiyan@google.com> From: Miaohe Lin Message-ID: <84a0b176-8534-e03a-9e6e-400c74ddab0b@huawei.com> Date: Tue, 9 Jun 2026 11:44:52 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 In-Reply-To: <20260531055829.3636554-2-jiaqiyan@google.com> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-ClientProxiedBy: kwepems200001.china.huawei.com (7.221.188.67) To kwepemq500010.china.huawei.com (7.202.194.235) On 2026/5/31 13:58, 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 in free_pages_prepare() as > a shortcut and is only invoked if PG_has_hwpoisoned indicates > HWPoison page exists and after checks and preparations in > free_pages_prepare() all succeeded. free_has_hwpoisoned() then > can re-use free_prepared_contig_range() [4] to decompose healthy > ranges into the largest possible chunks of different orders. > Every chunk meets the requirements to be freed via free_one_page(). > > 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 > [4] https://lore.kernel.org/all/20260401101634.2868165-2-usama.anjum@arm.com > > Signed-off-by: Jiaqi Yan Thanks for your update. This patch looks good to me while some comments below. > --- > mm/page_alloc.c | 85 +++++++++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 85 insertions(+) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index e47679e7a9db..03df929abca6 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -208,6 +208,7 @@ gfp_t gfp_allowed_mask __read_mostly = GFP_BOOT_MASK; > unsigned int pageblock_order __read_mostly; > #endif > > +static void free_has_hwpoisoned(struct page *page, unsigned int order); > static void __free_pages_ok(struct page *page, unsigned int order, > fpi_t fpi_flags); > static void reserve_highatomic_pageblock(struct page *page, int order, > @@ -1309,6 +1310,14 @@ static inline void pgalloc_tag_sub_pages(struct alloc_tag *tag, unsigned int nr) > > #endif /* CONFIG_MEM_ALLOC_PROFILING */ > > +/* > + * Returns > + * - true: checks and preparations all good, caller can proceed freeing. > + * - false: do not proceed freeing for one of the following reasons: > + * 1. Some check failed so it is not safe to proceed freeing. > + * 2. A compound page has some HWPoison pages. The healthy pages > + * are already safely freed, and the HWPoison ones isolated. > + */ > static __always_inline bool __free_pages_prepare(struct page *page, > unsigned int order, fpi_t fpi_flags) > { > @@ -1317,6 +1326,15 @@ 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); > + /* > + * When dealing with compound page, PG_has_hwpoisoned is cleared > + * with PAGE_FLAGS_SECOND. So the check must be done first. > + * > + * Note we can't exclude PG_has_hwpoisoned from PAGE_FLAGS_SECOND. > + * Because PG_has_hwpoisoned == PG_active, free_page_is_bad() will > + * confuse and complaint that the first tail page is still active. > + */ > + bool should_fhh = compound && folio_test_has_hwpoisoned(folio); > > if (fpi_flags & FPI_PREPARED) > return true; > @@ -1443,6 +1461,16 @@ static __always_inline bool __free_pages_prepare(struct page *page, > > debug_pagealloc_unmap_pages(page, 1 << order); > > + /* > + * After breaking down compound page and dealing with page metadata > + * (e.g. page owner and page alloc tags), take a shortcut if this > + * was a compound page containing certain HWPoison subpages. > + */ > + if (should_fhh) { > + free_has_hwpoisoned(page, order); > + return false; > + } When the code reaches here, the hwpoisoned pages have passed through kernel_poison_pages, kasan_poison_pages, kernel_init_pages, arch_free_page... These functions might write to the hwpoisoned pages. Is it safe to do so? > + > return true; > } > > @@ -6936,6 +6964,63 @@ void __free_contig_range(unsigned long pfn, unsigned long nr_pages) > __free_contig_range_common(pfn, nr_pages, /* is_frozen= */ false); > } > > +/* > + * Given a high-order compound page containing certain number of HWPoison > + * pages, free only the healthy ones. > + * > + * Pages must have passed free_pages_prepare(). Even if having HWPoison > + * pages, breaking down compound page and updating 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 cause nontrivial overhead. > + * So only use this when the compound page contains HWPoison page(s). > + * > + * This implementation needs rework in memdesc world. > + */ > +static void free_has_hwpoisoned(struct page *page, unsigned int order) > +{ > + 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; > + > + VM_WARN_ON(order == 0); > + VM_WARN_ON(page->flags.f & PAGE_FLAGS_CHECK_AT_PREP); > + > + while (curr < end_pfn) { > + next = curr; > + > + while (next < end_pfn && !PageHWPoison(pfn_to_page(next))) > + ++next; > + > + if (next != end_pfn && PageHWPoison(pfn_to_page(next))) { Check next != end_pfn should be enough. If we have next != end_pfn, we must have PageHWPoison(pfn_to_page(next)) or we can't exit from above while loop. Or am I miss something? Thanks. .