From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-189.mta0.migadu.com (out-189.mta0.migadu.com [91.218.175.189]) (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 47D54207DEE for ; Mon, 28 Apr 2025 12:50:28 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.189 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1745844632; cv=none; b=gbr1y9qCm/vo6S7C1BSLdxeFAzjiXmNRC7F3XFkH9W642adAEtmihqFhwPBjUO6m0BKjDnlnMkpIz1D0CQsDRB0EVAs8SdKc7KIxldpMSHH7OQas63tsYNOYprHdWMxempWvDCtQanCGIbCBEXA4+whQcX7idZzqY/hWTo/jckM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1745844632; c=relaxed/simple; bh=OWEBkh9dJy8wXuClxzycwoqSCFuQpJAKN5nd/kkI6uE=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=O/9jdzZBiHjMNhIPfWG3tkBPdYvK0/2Vyf/fN1W9lf3AeRIJNVf+rihww9dpt/od2w/gHABzBcYza4uLGHxknoqtwMFtkNkZIsZ2V381M5WSvPF2suO83ypf2QFgyNexVkw/5XIhDmYOsew2AVwTPeBY5wEZFBg3sb9rx8A5azc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=IVDg/78T; arc=none smtp.client-ip=91.218.175.189 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="IVDg/78T" Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1745844626; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=tmoFP7mWK1xDtxpxC3gMfuoxF1w2bYb3YT1RZ1atP8s=; b=IVDg/78TnwGssY/I/XW2WmOiRAnxxN48wxv1DWSOCn3YYb121+/64IkBo8+FUsCQdf9s0r O4aEsbZgKEok2xAK7cR2Jra+qNt2wSy6aLTx/92JqIYlczVAdJnhq0Wp4jK84B+ExiHoYm jE+4B/I/DSK0Aikia6yGoAONLSl/tRw= Date: Mon, 28 Apr 2025 20:50:11 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH 6/7] mm: Batch around can_change_pte_writable() Content-Language: en-US To: Dev Jain , akpm@linux-foundation.org Cc: ryan.roberts@arm.com, david@redhat.com, willy@infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, catalin.marinas@arm.com, will@kernel.org, Liam.Howlett@oracle.com, lorenzo.stoakes@oracle.com, vbabka@suse.cz, jannh@google.com, anshuman.khandual@arm.com, peterx@redhat.com, joey.gouly@arm.com, ioworker0@gmail.com, baohua@kernel.org, kevin.brodsky@arm.com, quic_zhenhuah@quicinc.com, christophe.leroy@csgroup.eu, yangyicong@hisilicon.com, linux-arm-kernel@lists.infradead.org, namit@vmware.com, hughd@google.com, yang@os.amperecomputing.com, ziy@nvidia.com References: <20250428120414.12101-1-dev.jain@arm.com> <20250428120414.12101-7-dev.jain@arm.com> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Lance Yang In-Reply-To: <20250428120414.12101-7-dev.jain@arm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT Hey Dev, On 2025/4/28 20:04, Dev Jain wrote: > In preparation for patch 7, we need to properly batch around > can_change_pte_writable(). We batch around pte_needs_soft_dirty_wp() by > the corresponding fpb flag, we batch around the page-anon exclusive check > using folio_maybe_mapped_shared(); modify_prot_start_ptes() collects the > dirty and access bits across the batch, therefore batching across > pte_dirty(): this is correct since the dirty bit on the PTE really > is just an indication that the folio got written to, so even if > the PTE is not actually dirty (but one of the PTEs in the batch is), > the wp-fault optimization can be made. > > Signed-off-by: Dev Jain > --- > include/linux/mm.h | 4 ++-- > mm/gup.c | 2 +- > mm/huge_memory.c | 4 ++-- > mm/memory.c | 6 +++--- > mm/mprotect.c | 9 ++++++--- > 5 files changed, 14 insertions(+), 11 deletions(-) > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index 5eb0d77c4438..ffa02e15863f 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -2710,8 +2710,8 @@ int get_cmdline(struct task_struct *task, char *buffer, int buflen); > #define MM_CP_UFFD_WP_ALL (MM_CP_UFFD_WP | \ > MM_CP_UFFD_WP_RESOLVE) > > -bool can_change_pte_writable(struct vm_area_struct *vma, unsigned long addr, > - pte_t pte); > +bool can_change_ptes_writable(struct vm_area_struct *vma, unsigned long addr, > + pte_t pte, struct folio *folio, unsigned int nr); > extern long change_protection(struct mmu_gather *tlb, > struct vm_area_struct *vma, unsigned long start, > unsigned long end, unsigned long cp_flags); > diff --git a/mm/gup.c b/mm/gup.c > index 84461d384ae2..6a605fc5f2cb 100644 > --- a/mm/gup.c > +++ b/mm/gup.c > @@ -614,7 +614,7 @@ static inline bool can_follow_write_common(struct page *page, > return false; > > /* > - * See can_change_pte_writable(): we broke COW and could map the page > + * See can_change_ptes_writable(): we broke COW and could map the page > * writable if we have an exclusive anonymous page ... > */ > return page && PageAnon(page) && PageAnonExclusive(page); > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index 28c87e0e036f..e5496c0d9e7e 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -2032,12 +2032,12 @@ static inline bool can_change_pmd_writable(struct vm_area_struct *vma, > return false; > > if (!(vma->vm_flags & VM_SHARED)) { > - /* See can_change_pte_writable(). */ > + /* See can_change_ptes_writable(). */ > page = vm_normal_page_pmd(vma, addr, pmd); > return page && PageAnon(page) && PageAnonExclusive(page); > } > > - /* See can_change_pte_writable(). */ > + /* See can_change_ptes_writable(). */ > return pmd_dirty(pmd); > } > > diff --git a/mm/memory.c b/mm/memory.c > index b9e8443aaa86..b1fda3de8d27 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -750,7 +750,7 @@ static void restore_exclusive_pte(struct vm_area_struct *vma, > pte = pte_mkuffd_wp(pte); > > if ((vma->vm_flags & VM_WRITE) && > - can_change_pte_writable(vma, address, pte)) { > + can_change_ptes_writable(vma, address, pte, NULL, 1)) { > if (folio_test_dirty(folio)) > pte = pte_mkdirty(pte); > pte = pte_mkwrite(pte, vma); > @@ -5767,7 +5767,7 @@ static void numa_rebuild_large_mapping(struct vm_fault *vmf, struct vm_area_stru > ptent = pte_modify(ptent, vma->vm_page_prot); > writable = pte_write(ptent); > if (!writable && pte_write_upgrade && > - can_change_pte_writable(vma, addr, ptent)) > + can_change_ptes_writable(vma, addr, ptent, NULL, 1)) > writable = true; > } > > @@ -5808,7 +5808,7 @@ static vm_fault_t do_numa_page(struct vm_fault *vmf) > */ > writable = pte_write(pte); > if (!writable && pte_write_upgrade && > - can_change_pte_writable(vma, vmf->address, pte)) > + can_change_ptes_writable(vma, vmf->address, pte, NULL, 1)) > writable = true; > > folio = vm_normal_folio(vma, vmf->address, pte); > diff --git a/mm/mprotect.c b/mm/mprotect.c > index 33eabc995584..362fd7e5457d 100644 > --- a/mm/mprotect.c > +++ b/mm/mprotect.c > @@ -40,8 +40,8 @@ > > #include "internal.h" > > -bool can_change_pte_writable(struct vm_area_struct *vma, unsigned long addr, > - pte_t pte) > +bool can_change_ptes_writable(struct vm_area_struct *vma, unsigned long addr, > + pte_t pte, struct folio *folio, unsigned int nr) > { > struct page *page; > > @@ -67,6 +67,9 @@ bool can_change_pte_writable(struct vm_area_struct *vma, unsigned long addr, > * write-fault handler similarly would map them writable without > * any additional checks while holding the PT lock. > */ > + if (unlikely(nr != 1)) > + return !folio_maybe_mapped_shared(folio); > + > page = vm_normal_page(vma, addr, pte); > return page && PageAnon(page) && PageAnonExclusive(page); > } IIUC, As mentioned in the comment above, we should do the same anonymous check to large folios. And folio_maybe_mapped_shared() already handles both order-0 and large folios nicely, so we could simplify the logic as follows: diff --git a/mm/mprotect.c b/mm/mprotect.c index 1605e89349d2..df56a30bb241 100644 --- a/mm/mprotect.c +++ b/mm/mprotect.c @@ -43,8 +43,6 @@ bool can_change_ptes_writable(struct vm_area_struct *vma, unsigned long addr, pte_t pte, struct folio *folio, unsigned int nr) { - struct page *page; - if (WARN_ON_ONCE(!(vma->vm_flags & VM_WRITE))) return false; @@ -67,11 +65,7 @@ bool can_change_ptes_writable(struct vm_area_struct *vma, unsigned long addr, * write-fault handler similarly would map them writable without * any additional checks while holding the PT lock. */ - if (unlikely(nr != 1)) - return !folio_maybe_mapped_shared(folio); - - page = vm_normal_page(vma, addr, pte); - return page && PageAnon(page) && PageAnonExclusive(page); + return folio_test_anon(folio) && !folio_maybe_mapped_shared(folio); } VM_WARN_ON_ONCE(is_zero_pfn(pte_pfn(pte)) && pte_dirty(pte)); -- Thanks, Lance > @@ -222,7 +225,7 @@ static long change_pte_range(struct mmu_gather *tlb, > */ > if ((cp_flags & MM_CP_TRY_CHANGE_WRITABLE) && > !pte_write(ptent) && > - can_change_pte_writable(vma, addr, ptent)) > + can_change_ptes_writable(vma, addr, ptent, folio, 1)) > ptent = pte_mkwrite(ptent, vma); > > ptep_modify_prot_commit(vma, addr, pte, oldpte, ptent);