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 3D72B5B5D2; Mon, 29 Jan 2024 11:05:16 +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=1706526320; cv=none; b=tL8biV2NZc80blawDH8YFl8GBf/l712bMB/B8E6HuBHND92wHVwBkydHztSOCQ8uSQ9A5ozEHWQEh9H1fRoSiP8k9OpZc6E44wbpScrszVlkBzPFduhP7KdBxmOJa4LP2rE5UasQJET5lqTFqDFp9lkQK4WFKL22ReuyKxGPw6g= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1706526320; c=relaxed/simple; bh=z7vCLiWnpGh25FZ1AIsxRGIMMKUxxU4DDA304c/YCcQ=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=S4m59RpFt+gvoZI79IXbxwXXc8wW9yAHoRpqnw+tEXI6lIcDJERCYPcedWy0PVTeIgvlxUYv2oaHOg3W+yY31Dh8Dyg/zvcpM/JEBZD65j86yXOPlS5VnpFaQLK44X+rn4gR7gdYt2xfozjKkq7D7f3RvGPsBUF8UeB1gusme6k= 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; 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 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 34BDC1FB; Mon, 29 Jan 2024 03:06:00 -0800 (PST) Received: from [10.57.65.9] (unknown [10.57.65.9]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id D2ECE3F5A1; Mon, 29 Jan 2024 03:05:12 -0800 (PST) Message-ID: <7a34378c-3b1d-4ce1-80f8-938796ff3e6c@arm.com> Date: Mon, 29 Jan 2024 11:05:11 +0000 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 14/15] mm/memory: ignore dirty/accessed/soft-dirty bits in folio_pte_batch() Content-Language: en-GB To: David Hildenbrand , linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, Andrew Morton , Matthew Wilcox , Russell King , Catalin Marinas , Will Deacon , Dinh Nguyen , Michael Ellerman , Nicholas Piggin , Christophe Leroy , "Aneesh Kumar K.V" , "Naveen N. Rao" , Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexander Gordeev , Gerald Schaefer , Heiko Carstens , Vasily Gorbik , Christian Borntraeger , Sven Schnelle , "David S. Miller" , linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, sparclinux@vger.kernel.org References: <20240125193227.444072-1-david@redhat.com> <20240125193227.444072-15-david@redhat.com> From: Ryan Roberts In-Reply-To: <20240125193227.444072-15-david@redhat.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 25/01/2024 19:32, David Hildenbrand wrote: > Let's always ignore the accessed/young bit: we'll always mark the PTE > as old in our child process during fork, and upcoming users will > similarly not care. > > Ignore the dirty bit only if we don't want to duplicate the dirty bit > into the child process during fork. Maybe, we could just set all PTEs > in the child dirty if any PTE is dirty. For now, let's keep the behavior > unchanged, this can be optimized later if required. > > Ignore the soft-dirty bit only if the bit doesn't have any meaning in > the src vma, and similarly won't have any in the copied dst vma. > > For now, we won't bother with the uffd-wp bit. > > Signed-off-by: David Hildenbrand Reviewed-by: Ryan Roberts > --- > mm/memory.c | 36 +++++++++++++++++++++++++++++++----- > 1 file changed, 31 insertions(+), 5 deletions(-) > > diff --git a/mm/memory.c b/mm/memory.c > index 4d1be89a01ee0..b3f035fe54c8d 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -953,24 +953,44 @@ static __always_inline void __copy_present_ptes(struct vm_area_struct *dst_vma, > set_ptes(dst_vma->vm_mm, addr, dst_pte, pte, nr); > } > > +/* Flags for folio_pte_batch(). */ > +typedef int __bitwise fpb_t; > + > +/* Compare PTEs after pte_mkclean(), ignoring the dirty bit. */ > +#define FPB_IGNORE_DIRTY ((__force fpb_t)BIT(0)) > + > +/* Compare PTEs after pte_clear_soft_dirty(), ignoring the soft-dirty bit. */ > +#define FPB_IGNORE_SOFT_DIRTY ((__force fpb_t)BIT(1)) > + > +static inline pte_t __pte_batch_clear_ignored(pte_t pte, fpb_t flags) > +{ > + if (flags & FPB_IGNORE_DIRTY) > + pte = pte_mkclean(pte); > + if (likely(flags & FPB_IGNORE_SOFT_DIRTY)) > + pte = pte_clear_soft_dirty(pte); > + return pte_mkold(pte); > +} > + > /* > * Detect a PTE batch: consecutive (present) PTEs that map consecutive > * pages of the same folio. > * > - * All PTEs inside a PTE batch have the same PTE bits set, excluding the PFN. > + * All PTEs inside a PTE batch have the same PTE bits set, excluding the PFN, > + * the accessed bit, dirty bit (with FPB_IGNORE_DIRTY) and soft-dirty bit > + * (with FPB_IGNORE_SOFT_DIRTY). > */ > static inline int folio_pte_batch(struct folio *folio, unsigned long addr, > - pte_t *start_ptep, pte_t pte, int max_nr) > + pte_t *start_ptep, pte_t pte, int max_nr, fpb_t flags) > { > unsigned long folio_end_pfn = folio_pfn(folio) + folio_nr_pages(folio); > const pte_t *end_ptep = start_ptep + max_nr; > - pte_t expected_pte = pte_next_pfn(pte); > + pte_t expected_pte = __pte_batch_clear_ignored(pte_next_pfn(pte), flags); > pte_t *ptep = start_ptep + 1; > > VM_WARN_ON_FOLIO(!pte_present(pte), folio); > > while (ptep != end_ptep) { > - pte = ptep_get(ptep); > + pte = __pte_batch_clear_ignored(ptep_get(ptep), flags); > > if (!pte_same(pte, expected_pte)) > break; > @@ -1004,6 +1024,7 @@ copy_present_ptes(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma > { > struct page *page; > struct folio *folio; > + fpb_t flags = 0; > int err, nr; > > page = vm_normal_page(src_vma, addr, pte); > @@ -1018,7 +1039,12 @@ copy_present_ptes(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma > * by keeping the batching logic separate. > */ > if (unlikely(!*prealloc && folio_test_large(folio) && max_nr != 1)) { > - nr = folio_pte_batch(folio, addr, src_pte, pte, max_nr); > + if (src_vma->vm_flags & VM_SHARED) > + flags |= FPB_IGNORE_DIRTY; > + if (!vma_soft_dirty_enabled(src_vma)) > + flags |= FPB_IGNORE_SOFT_DIRTY; > + > + nr = folio_pte_batch(folio, addr, src_pte, pte, max_nr, flags); > folio_ref_add(folio, nr); > if (folio_test_anon(folio)) { > if (unlikely(folio_try_dup_anon_rmap_ptes(folio, page,