From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 D326F36605E; Fri, 6 Mar 2026 12:21:48 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772799708; cv=none; b=YyORlxNyitG5lX+aUBui5M+gNyd87+DBRILsGBZqyL1XsFxAwlv5yhhnWmg885RL7G9DqLkVak34szXf8kGWFWJX15qF+eVjWyV5912cBQOrRu34cKIu8mvTEpw69v9Y5/X2us87chzrjsE3sWVJhQONvw3u4Gx86PTWBxVg8zE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772799708; c=relaxed/simple; bh=theG/LCt2/q2eE4jZPVvO5dWH6DfzprovWLt+cDnxxE=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=HSm4UuHaaKXjqR9/2AffRtgrn22rUTjAMjZSgiC+XSC3EPWzQfdhcrirNcwXa4weneTlgBcCWB2/8clSX9wFMnOKEI3qN/+9RGECT5A3FJFvCbOZjRJO4JG4OY7wwHtpNyKP/XjjiNtk+ZhloZazDuUg2f0nNOikVsGR53ELNn0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=h5AYGafZ; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="h5AYGafZ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id DC2EEC4CEF7; Fri, 6 Mar 2026 12:21:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1772799708; bh=theG/LCt2/q2eE4jZPVvO5dWH6DfzprovWLt+cDnxxE=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=h5AYGafZBAupVubVI+ZD7t499uAUfoIBiWhpl8owqkPKw6XrDaEVq2gk6V3VMTbJG I4jRzHR0ZgmZkpNFwz4WPgqzlj/ZTXG8Mkg6mu7rnyphpzPSp0u7fh1+VK9oWLl6gi IDaaFcFprJbRbe9bTzXRL2TSF66F78vemrV5U33fTWh+G/lmL2lf9YKdm5HPHC4unn ZD1xuMdPWyTYHNQLOcZ7Z+EV+KFd74oVVcNcMiIFZxDCm23EI+oRIIIQqgBzscf/du 1PqvIt+BJZaIL/QfENv95huWxRehRctl1ISCOa4xhZ4a1heXH/LVdrvC2Qdmxny09h GIoNXwDaiAUHQ== Date: Fri, 6 Mar 2026 12:21:45 +0000 From: "Lorenzo Stoakes (Oracle)" To: "David Hildenbrand (Arm)" Cc: linux-kernel@vger.kernel.org, "linux-mm @ kvack . org" , Andrew Morton , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Jann Horn , Pedro Falcato , David Rientjes , Shakeel Butt , "Matthew Wilcox (Oracle)" , Alice Ryhl , Madhavan Srinivasan , Michael Ellerman , Christian Borntraeger , Janosch Frank , Claudio Imbrenda , Alexander Gordeev , Gerald Schaefer , Heiko Carstens , Vasily Gorbik , Jarkko Sakkinen , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Greg Kroah-Hartman , Arve =?utf-8?B?SGrDuG5uZXbDpWc=?= , Todd Kjos , Christian Brauner , Carlos Llamas , Ian Abbott , H Hartley Sweeten , Jani Nikula , Joonas Lahtinen , Rodrigo Vivi , Tvrtko Ursulin , David Airlie , Simona Vetter , Jason Gunthorpe , Leon Romanovsky , Dimitri Sivanich , Arnd Bergmann , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Peter Zijlstra , Arnaldo Carvalho de Melo , Namhyung Kim , Andy Lutomirski , Vincenzo Frascino , Eric Dumazet , Neal Cardwell , "David S. Miller" , David Ahern , Jakub Kicinski , Paolo Abeni , Miguel Ojeda , linuxppc-dev@lists.ozlabs.org, kvm@vger.kernel.org, linux-s390@vger.kernel.org, linux-sgx@vger.kernel.org, intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, linux-rdma@vger.kernel.org, bpf@vger.kernel.org, linux-perf-users@vger.kernel.org, linux-fsdevel@vger.kernel.org, netdev@vger.kernel.org, rust-for-linux@vger.kernel.org, x86@kernel.org Subject: Re: [PATCH v1 09/16] mm/memory: convert details->even_cows into details->skip_cows Message-ID: <091ce280-9204-4b85-bf39-5e2a61e3d0ba@lucifer.local> References: <20260227200848.114019-1-david@kernel.org> <20260227200848.114019-10-david@kernel.org> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260227200848.114019-10-david@kernel.org> On Fri, Feb 27, 2026 at 09:08:40PM +0100, David Hildenbrand (Arm) wrote: > The current semantics are confusing: simply because someone specifies an > empty zap_detail struct suddenly makes should_zap_cows() behave > differently. The default should be to also zap CoW'ed anonymous pages. > > Really only unmap_mapping_pages() and friends want to skip zapping of > these anon folios. > > So let's invert the meaning; turn the confusing "reclaim_pt" check that > overrides other properties in should_zap_cows() into a safety check. > > Note that the only caller that sets reclaim_pt=true is > madvise_dontneed_single_vma(), which wants to zap any pages. > > Signed-off-by: David Hildenbrand (Arm) This is another nice change. I have some tweak suggestions below, but past experience suggests to me it's quite possible you do what I ask in subsequent patches, will see :) Anyway overall LGTM, so: Reviewed-by: Lorenzo Stoakes (Oracle) > --- > include/linux/mm.h | 2 +- > mm/madvise.c | 1 - > mm/memory.c | 12 ++++++------ > 3 files changed, 7 insertions(+), 8 deletions(-) > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index d3ef586ee1c0..21b67c203e62 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -2798,7 +2798,7 @@ extern void pagefault_out_of_memory(void); > */ > struct zap_details { > struct folio *single_folio; /* Locked folio to be unmapped */ > - bool even_cows; /* Zap COWed private pages too? */ > + bool skip_cows; /* Do not zap COWed private pages */ > bool reclaim_pt; /* Need reclaim page tables? */ > zap_flags_t zap_flags; /* Extra flags for zapping */ > }; > diff --git a/mm/madvise.c b/mm/madvise.c > index 557a360f7919..b51f216934f3 100644 > --- a/mm/madvise.c > +++ b/mm/madvise.c > @@ -853,7 +853,6 @@ static long madvise_dontneed_single_vma(struct madvise_behavior *madv_behavior) > struct madvise_behavior_range *range = &madv_behavior->range; > struct zap_details details = { > .reclaim_pt = true, > - .even_cows = true, > }; > > zap_page_range_single_batched( > diff --git a/mm/memory.c b/mm/memory.c > index fdcd2abf29c2..7d7c24c6917c 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -1554,11 +1554,13 @@ copy_page_range(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma) > static inline bool should_zap_cows(struct zap_details *details) Not sure if you fix up later, but we should probably change this function to should_skip_cows() to keep everything consistent, otherwise this is a bit weird and confusing. > { > /* By default, zap all pages */ > - if (!details || details->reclaim_pt) > + if (!details) > return true; > > + VM_WARN_ON_ONCE(details->skip_cows && details->reclaim_pt); > + > /* Or, we zap COWed pages only if the caller wants to */ > - return details->even_cows; > + return !details->skip_cows; > } > > /* Decides whether we should zap this folio with the folio pointer specified */ > @@ -2149,8 +2151,6 @@ void unmap_vmas(struct mmu_gather *tlb, struct unmap_desc *unmap) > struct mmu_notifier_range range; > struct zap_details details = { > .zap_flags = ZAP_FLAG_DROP_MARKER | ZAP_FLAG_UNMAP, > - /* Careful - we need to zap private pages too! */ > - .even_cows = true, > }; > > vma = unmap->first; > @@ -4282,7 +4282,7 @@ void unmap_mapping_folio(struct folio *folio) > first_index = folio->index; > last_index = folio_next_index(folio) - 1; > > - details.even_cows = false; > + details.skip_cows = true; > details.single_folio = folio; > details.zap_flags = ZAP_FLAG_DROP_MARKER; > > @@ -4312,7 +4312,7 @@ void unmap_mapping_pages(struct address_space *mapping, pgoff_t start, > pgoff_t first_index = start; > pgoff_t last_index = start + nr - 1; > > - details.even_cows = even_cows; > + details.skip_cows = !even_cows; Not sure if you clean up later, but seems sensible to cascade the change into the local boolean here. > if (last_index < first_index) > last_index = ULONG_MAX; > > -- > 2.43.0 >