From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 848CC2E22B5 for ; Fri, 24 Jul 2026 05:05:46 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784869550; cv=none; b=OdENFwU7A3VRyGrNYq8AJvG2+1ZJF6Yg9wvZ0SyEMr3+06fTQvHeFoR30y1DHxMK3qTj+mlOF5F1mElOrwLzeT+w16TK1N2p0Xmq/tJrtmNk6Peiz5aowliZOyo6tTWX2zay2Hf6wktqBGT0T3o4KN7NG+zGyYhRP3um37lQ5mA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784869550; c=relaxed/simple; bh=9z1bk8upQShwtNFSq0+22MPZuPf4R/Mr2jz7W5iVWLQ=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=iRQrSvB4J7jOhkYc5wasKXtcQsKDGtmhsTIAXKAESrjuO5bsHsd2mE8cBQKLPslDM4DAdPOY7UNrlC7hDLn6fMl8bVH+FnXzd/s0BhHYl40oG30Yh8tczHp75kronuiwOfGpF0Nj2trH5PdOmGkaZkFcfe/CBWKoZYk7/6YQOEI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b=GUmn4JfB; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b="GUmn4JfB" Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id E9E9B1477; Thu, 23 Jul 2026 22:05:40 -0700 (PDT) Received: from [10.164.148.44] (MacBook-Pro.blr.arm.com [10.164.148.44]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id DE9113F86F; Thu, 23 Jul 2026 22:05:40 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1784869545; bh=9z1bk8upQShwtNFSq0+22MPZuPf4R/Mr2jz7W5iVWLQ=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=GUmn4JfB0jh0NLkd/QxuENHfGYYuCh4n25zdfDVPY0Ej30DIrxWLwvOm0/eySV8Kf pDQ5QEBRaNUX8aDLq4hX/UCYJciU8PSbEOmcJRk8tR/aA316X5X8xG9X66sz4fb0zF KaFk4h0OpI6u8PnOeMcq20BAXqsc7d92Dw2b8cgw= Message-ID: Date: Fri, 24 Jul 2026 10:35:34 +0530 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 v2 1/5] mm/rmap: convert page -> folio for hwpoison checks To: "Lorenzo Stoakes (ARM)" Cc: akpm@linux-foundation.org, david@kernel.org, muchun.song@linux.dev, osalvador@suse.de, riel@surriel.com, liam@infradead.org, vbabka@kernel.org, harry@kernel.org, jannh@google.com, lance.yang@linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, ryan.roberts@arm.com, anshuman.khandual@arm.com References: <20260710055915.638659-1-dev.jain@arm.com> <20260710055915.638659-2-dev.jain@arm.com> Content-Language: en-US From: Dev Jain In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 23/07/26 10:45 pm, Lorenzo Stoakes (ARM) wrote: > On Fri, Jul 10, 2026 at 05:59:10AM +0000, Dev Jain wrote: >> try_to_unmap() receives hugetlb folios only from the hwpoison path. > > Horrifying :) > >> hugetlb_update_hwpoison() sets the hugetlb folio's head-page >> hwpoison bit, and page_vma_mapped_walk() reports the hugetlb mapping at >> the head PFN, so the previous PageHWPoison(subpage) check happened to >> work for hugetlb. >> >> For non-hugetlb folios, unmap_poisoned_folio() currently rejects large >> folios before calling try_to_unmap(). Hence it is always the case that >> if try_to_unmap_one() handles an hwpoisoned folio, then the head page is >> marked with the poison bit. >> >> Therefore, convert the poisoned subpage checks to folio_test_hwpoison(). >> >> No functional change intended, except that, while at it, >> convert VM_BUG_* to VM_WARN_*. >> >> Acked-by: David Hildenbrand (Arm) >> Signed-off-by: Dev Jain > > Small nit below but generally LGTM so: > > Reviewed-by: Lorenzo Stoakes (ARM) > >> --- >> mm/rmap.c | 13 +++++++++---- >> 1 file changed, 9 insertions(+), 4 deletions(-) >> >> diff --git a/mm/rmap.c b/mm/rmap.c >> index 9939400e77c79..dbb077f8443e3 100644 >> --- a/mm/rmap.c >> +++ b/mm/rmap.c >> @@ -2122,10 +2122,11 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma, >> bool anon = folio_test_anon(folio); >> >> /* >> - * The try_to_unmap() is only passed a hugetlb page >> - * in the case where the hugetlb page is poisoned. >> + * The try_to_unmap() is only passed a hugetlb folio >> + * in the case where the hugetlb folio contains a >> + * poisoned page. >> */ >> - VM_BUG_ON_PAGE(!PageHWPoison(subpage), subpage); >> + VM_WARN_ON_FOLIO(!folio_test_hwpoison(folio), folio); >> /* >> * huge_pmd_unshare may unmap an entire PMD page. >> * There is no way of knowing exactly which PMDs may >> @@ -2204,7 +2205,11 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma, >> /* Update high watermark before we lower rss */ >> update_hiwater_rss(mm); >> >> - if (PageHWPoison(subpage) && (flags & TTU_HWPOISON)) { >> + /* >> + * With TTU_HWPOISON, we only expect small folios or hugetlb >> + * folios here for now. >> + */ > > I think probably we can drop this? It seems implied by the code (David comment > similarly I think? :) I had posted a v3 here: https://lore.kernel.org/all/20260713050050.1017741-1-dev.jain@arm.com/ In that I had fixed this comment to drop "or hugetlb folios ..." . But I would still like to retain the "only expect small folios" comment, it adds cognitive load when I am reading try_to_unmap_one and then have to go read hwpoison code to figure that large folios would be split before coming here. > >> + if (folio_test_hwpoison(folio) && (flags & TTU_HWPOISON)) { >> pteval = swp_entry_to_pte(make_hwpoison_entry(subpage)); >> if (folio_test_hugetlb(folio)) { >> hugetlb_count_sub(folio_nr_pages(folio), mm); >> -- >> 2.43.0 >> > > Cheers, Lorenzo