From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists.ozlabs.org (lists.ozlabs.org [112.213.38.117]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 3C6D3C46CD2 for ; Tue, 30 Jan 2024 09:04:39 +0000 (UTC) Received: from boromir.ozlabs.org (localhost [IPv6:::1]) by lists.ozlabs.org (Postfix) with ESMTP id 4TPK455szSz3bpp for ; Tue, 30 Jan 2024 20:04:37 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=arm.com (client-ip=217.140.110.172; helo=foss.arm.com; envelope-from=ryan.roberts@arm.com; receiver=lists.ozlabs.org) Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lists.ozlabs.org (Postfix) with ESMTP id 4TPK3d6sVzz30Np for ; Tue, 30 Jan 2024 20:04:12 +1100 (AEDT) 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 7DCEA139F; Tue, 30 Jan 2024 01:04:24 -0800 (PST) Received: from [10.57.79.54] (unknown [10.57.79.54]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id CA66B3F738; Tue, 30 Jan 2024 01:03:37 -0800 (PST) Message-ID: <075975db-a59b-483a-95d7-0990442ebe6f@arm.com> Date: Tue, 30 Jan 2024 09:03:36 +0000 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1 6/9] mm/mmu_gather: define ENCODED_PAGE_FLAG_DELAY_RMAP Content-Language: en-GB To: David Hildenbrand , linux-kernel@vger.kernel.org References: <20240129143221.263763-1-david@redhat.com> <20240129143221.263763-7-david@redhat.com> From: Ryan Roberts In-Reply-To: <20240129143221.263763-7-david@redhat.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-arch@vger.kernel.org, linux-s390@vger.kernel.org, Alexander Gordeev , Christian Borntraeger , Arnd Bergmann , Vasily Gorbik , Peter Zijlstra , "Aneesh Kumar K.V" , linuxppc-dev@lists.ozlabs.org, Matthew Wilcox , linux-mm@kvack.org, Nick Piggin , Catalin Marinas , "Naveen N. Rao" , Andrew Morton , Will Deacon , Heiko Carstens , Sven Schnelle Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On 29/01/2024 14:32, David Hildenbrand wrote: > Nowadays, encoded pages are only used in mmu_gather handling. Let's > update the documentation, and define ENCODED_PAGE_BIT_DELAY_RMAP. While at > it, rename ENCODE_PAGE_BITS to ENCODED_PAGE_BITS. > > If encoded page pointers would ever be used in other context again, we'd > likely want to change the defines to reflect their context (e.g., > ENCODED_PAGE_FLAG_MMU_GATHER_DELAY_RMAP). For now, let's keep it simple. > > This is a preparation for using the remaining spare bit to indicate that > the next item in an array of encoded pages is a "nr_pages" argument and > not an encoded page. > > Signed-off-by: David Hildenbrand Reviewed-by: Ryan Roberts > --- > include/linux/mm_types.h | 17 +++++++++++------ > mm/mmu_gather.c | 5 +++-- > 2 files changed, 14 insertions(+), 8 deletions(-) > > diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h > index 8b611e13153e..1b89eec0d6df 100644 > --- a/include/linux/mm_types.h > +++ b/include/linux/mm_types.h > @@ -210,8 +210,8 @@ struct page { > * > * An 'encoded_page' pointer is a pointer to a regular 'struct page', but > * with the low bits of the pointer indicating extra context-dependent > - * information. Not super-common, but happens in mmu_gather and mlock > - * handling, and this acts as a type system check on that use. > + * information. Only used in mmu_gather handling, and this acts as a type > + * system check on that use. > * > * We only really have two guaranteed bits in general, although you could > * play with 'struct page' alignment (see CONFIG_HAVE_ALIGNED_STRUCT_PAGE) > @@ -220,21 +220,26 @@ struct page { > * Use the supplied helper functions to endcode/decode the pointer and bits. > */ > struct encoded_page; > -#define ENCODE_PAGE_BITS 3ul > + > +#define ENCODED_PAGE_BITS 3ul > + > +/* Perform rmap removal after we have flushed the TLB. */ > +#define ENCODED_PAGE_BIT_DELAY_RMAP 1ul > + > static __always_inline struct encoded_page *encode_page(struct page *page, unsigned long flags) > { > - BUILD_BUG_ON(flags > ENCODE_PAGE_BITS); > + BUILD_BUG_ON(flags > ENCODED_PAGE_BITS); > return (struct encoded_page *)(flags | (unsigned long)page); > } > > static inline unsigned long encoded_page_flags(struct encoded_page *page) > { > - return ENCODE_PAGE_BITS & (unsigned long)page; > + return ENCODED_PAGE_BITS & (unsigned long)page; > } > > static inline struct page *encoded_page_ptr(struct encoded_page *page) > { > - return (struct page *)(~ENCODE_PAGE_BITS & (unsigned long)page); > + return (struct page *)(~ENCODED_PAGE_BITS & (unsigned long)page); > } > > /* > diff --git a/mm/mmu_gather.c b/mm/mmu_gather.c > index ac733d81b112..6540c99c6758 100644 > --- a/mm/mmu_gather.c > +++ b/mm/mmu_gather.c > @@ -53,7 +53,7 @@ static void tlb_flush_rmap_batch(struct mmu_gather_batch *batch, struct vm_area_ > for (int i = 0; i < batch->nr; i++) { > struct encoded_page *enc = batch->encoded_pages[i]; > > - if (encoded_page_flags(enc)) { > + if (encoded_page_flags(enc) & ENCODED_PAGE_BIT_DELAY_RMAP) { > struct page *page = encoded_page_ptr(enc); > folio_remove_rmap_pte(page_folio(page), page, vma); > } > @@ -119,6 +119,7 @@ static void tlb_batch_list_free(struct mmu_gather *tlb) > bool __tlb_remove_page_size(struct mmu_gather *tlb, struct page *page, > bool delay_rmap, int page_size) > { > + int flags = delay_rmap ? ENCODED_PAGE_BIT_DELAY_RMAP : 0; > struct mmu_gather_batch *batch; > > VM_BUG_ON(!tlb->end); > @@ -132,7 +133,7 @@ bool __tlb_remove_page_size(struct mmu_gather *tlb, struct page *page, > * Add the page and check if we are full. If so > * force a flush. > */ > - batch->encoded_pages[batch->nr++] = encode_page(page, delay_rmap); > + batch->encoded_pages[batch->nr++] = encode_page(page, flags); > if (batch->nr == batch->max) { > if (!tlb_next_batch(tlb)) > return true;