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 75FA540860C for ; Tue, 7 Jul 2026 14:15:55 +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=1783433756; cv=none; b=L4ebzIExIAQqRAA0PWQavTvJ285fhLcvzvH0fa1+WVW9cBfF9rBySSSi2dB5kEd3gJ2Sfy5KWNs1GdGzxcGpKKzt78BqxXHIDLFJeyi81rXLlkRkYkkuYLOARbXiUyX5KucwsPnaOnqEFnAA0wCy0jPpTXjczX6EfhM9LWXDvt0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783433756; c=relaxed/simple; bh=3p47pq80g9oRLzBbRA/UQQZZBdnkb5KReT1HBRym5wg=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=gy8u0z5WhoQ1+qkyzXjCK7KoknppMmyCm83EGx4JM2Zs+BuDGy4TF3xLDF6FZQeDmkQNMjdEusCBwdQv89OLvu6phBRQ/MQ4feldU/q/HXJOGt4DDvZ6DWocdn/X/yoqe3ss0txM13jNwyGrk2p+34bmwonIT1KxwoYElikxLd4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=LTM7/J/L; 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="LTM7/J/L" Received: by smtp.kernel.org (Postfix) with ESMTPSA id C00141F000E9; Tue, 7 Jul 2026 14:15:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1783433755; bh=3Je8n/wdoymxGQHenCCf7yyFcACysXlS+ymbtqKSEW8=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=LTM7/J/LZeFUkiA0UYeYqmXv6kZhSrg7UVhYi52Mqw+clZlr+5XAvWHRjhC3+Q1Iz XLHdtDiil/mdzgCMRMzXfIDAxR9KEUp3AvBHbtYBFEbWUGB7wO12i5qNR6+dpsk1uH h4DKuXuFnGDRDBNVjcOQ0VISHnbVncUw/dOiXAXJcrnRNmsOKQ1r+IRQQOVpC419c4 vMN8mrOM6xmyG5zCcTDW3twLwjtRPJnffTmxLtoXCakesDSMeU6+hNahJLZwhsW3ga +o+xiytDm2FUF5ZkfKzjsDkWc7FzPRp/ssBuZPFHp1t6OAIQ8pfwYADa8O8Ay4VBKJ jcDX407DgCQ0Q== Message-ID: Date: Tue, 7 Jul 2026 16:15:50 +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 2/5] mm/rmap: Add try_to_unmap_hugetlb_one To: Dev Jain , akpm@linux-foundation.org, ljs@kernel.org, muchun.song@linux.dev, osalvador@suse.de Cc: 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: <20260707121128.373192-1-dev.jain@arm.com> <20260707121128.373192-3-dev.jain@arm.com> 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 7/7/26 14:11, Dev Jain wrote: > Simplify try_to_unmap_one() by separating the hugetlb parts into > try_to_unmap_hugetlb_one(). > > To understand the correctness of the refactoring, the following points > are noted: > > 1. try_to_unmap() is called for hugetlb folios only when they are > hwpoisoned. > > 2. A hugetlb VMA cannot be mlocked. > > 3. page_vma_mapped_walk() returns at most one hugetlb mapping in a VMA, > and that mapping points at the head PFN. > > 4. We won't ever process a softleaf entry that encodes a hugetlb folio; > hugetlb folios are never swapped out, migration entries will be > skipped (PVMW_MIGRATION not passed), and device-exclusive does not > work for hugetlb. > > 5. The hwpoison entry is constructed from the poisoned folio, just as in > the pre-refactor code. Any previous uffd-wp state is deliberately not > preserved for the hwpoison entry. > > 6. TTU_HWPOISON is always present; for it to not be present, either the > folio has to be in swapcache, or mapping_can_writeback() is true (see > unmap_poisoned_folio), none of which is true for hugetlb folios. > > 7. Hugetlb uses separate counters from normal rss counters, therefore > update_highwater_rss() need not be called. > > While at it: > > - Change VM_BUG_* to VM_WARN_*. > > - Do not declare variables which are only used once. > > - Use huge_pte_dirty() instead of pte_dirty(). > > - Add 3 VM_WARN_ON_ONCE asserting that TTU_HWPOISON should be present, > pte_present() must be true, and the pfn derived from the huge pte > must be that of the head of the hugetlb folio. > > Except the BUG->WARN change, no functional change intended. > > Suggested-by: David Hildenbrand > Signed-off-by: Dev Jain > --- > include/linux/hugetlb.h | 1 + > mm/rmap.c | 177 +++++++++++++++++++++------------------- > 2 files changed, 96 insertions(+), 82 deletions(-) > > diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h > index 4115076e4922a..bf7e163e3779d 100644 > --- a/include/linux/hugetlb.h > +++ b/include/linux/hugetlb.h > @@ -1271,6 +1271,7 @@ static inline void hugetlb_count_sub(long l, struct mm_struct *mm) > } > > pte_t huge_ptep_get(struct mm_struct *mm, unsigned long addr, pte_t *ptep); > +unsigned long huge_pte_dirty(pte_t pte); > > static inline pte_t huge_ptep_clear_flush(struct vm_area_struct *vma, > unsigned long addr, pte_t *ptep) > diff --git a/mm/rmap.c b/mm/rmap.c > index dbb077f8443e3..934773dfa2f2a 100644 > --- a/mm/rmap.c > +++ b/mm/rmap.c > @@ -1978,6 +1978,95 @@ static inline unsigned int folio_unmap_pte_batch(struct folio *folio, > FPB_RESPECT_WRITE | FPB_RESPECT_SOFT_DIRTY); > } > > +static bool try_to_unmap_hugetlb_one(struct folio *folio, > + struct vm_area_struct *vma, unsigned long address, void *arg) > +{ > + DEFINE_FOLIO_VMA_WALK(pvmw, folio, vma, address, 0); > + struct mmu_notifier_range range; > + enum ttu_flags flags = (enum ttu_flags)(long)arg; > + struct mm_struct *mm = vma->vm_mm; > + const unsigned long hsz = huge_page_size(hstate_vma(vma)); I would move const variables all the way up. > + bool ret = true; > + pte_t pteval; > + > + /* > + * The try_to_unmap() is only passed a hugetlb folio in the case > + * where the hugetlb folio is poisoned. > + */ > + VM_WARN_ON_FOLIO(!folio_test_hwpoison(folio), folio); > + VM_WARN_ON_ONCE(!(flags & TTU_HWPOISON)); > + > + range.end = vma_address_end(&pvmw); > + mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma->vm_mm, > + address, range.end); > + adjust_range_if_pmd_sharing_possible(vma, &range.start, &range.end); > + mmu_notifier_invalidate_range_start(&range); > + > + /* There is only a single mapping in a VMA. */ > + if (!page_vma_mapped_walk(&pvmw)) > + goto range_end; > + > + address = pvmw.address; Will address ever change due to the page_vma_mapped_walk()? I don't think so, right? So this can instead become a VM_WARN_ON_ONCE, maybe? Nothing else jumped at me, much clearer to me. Acked-by: David Hildenbrand (Arm) -- Cheers, David