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b=1eDi1aFNs3Up7hg68+tzcLXlQmtYG+Rjn7OjkCaE09QrgYshaLno0Sr9g50pUA9za 8wKei6dV52DSkpwvoHrI6kRfW+qyoTV5lxxfddYuXlIHsjmkk3KwGb2nM9OHlPIDvT v88QXWRdkWSyqDF1kZnmg001pde8cmzkhaPTXYWo= Date: Mon, 9 Sep 2024 15:25:46 -0700 From: Andrew Morton To: Peter Xu Cc: Yan Zhao , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Gavin Shan , Catalin Marinas , x86@kernel.org, Ingo Molnar , Paolo Bonzini , Dave Hansen , Thomas Gleixner , Alistair Popple , kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Sean Christopherson , Oscar Salvador , Jason Gunthorpe , Borislav Petkov , Zi Yan , Axel Rasmussen , David Hildenbrand , Will Deacon , Kefeng Wang , Alex Williamson Subject: Re: [PATCH v2 07/19] mm/fork: Accept huge pfnmap entries Message-Id: <20240909152546.4ef47308e560ce120156bc35@linux-foundation.org> In-Reply-To: References: <20240826204353.2228736-1-peterx@redhat.com> <20240826204353.2228736-8-peterx@redhat.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 1F1CD40007 X-Stat-Signature: 5jhqt87ebq4ceit88w76b6wcdbmnuq1k X-Rspam-User: X-HE-Tag: 1725920748-248799 X-HE-Meta: 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 ZXZL482a ElRgunnYeZisF+/oJ9mbpGRMVtKWEhKbMYjjOMqdRPZg+oE1N4WBc6kVu27/r2IEjqaiQqU2C0rGzCeAkl52ADeLBH0a3BawNpPzAiHOEWS+z4H53WVqLJHyK/8TU7nB+lNSNVP+J8Or9zLGUplN1DWLy75dUfgc50OpxD7gSL1OhXlKVbuE80Ib9fGmuALGWO3wC2oFi+i33KkwgwahnpD6slka8oovhlNoNQt3Gvfkc9GhqMFcFn2udurRpGWEzcn+gGhCuzIIWQBrESJ9Q1lsJYw== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, 3 Sep 2024 17:23:38 -0400 Peter Xu wrote: > > > @@ -1686,8 +1706,11 @@ int copy_huge_pud(struct mm_struct *dst_mm, struct mm_struct *src_mm, > > > * TODO: once we support anonymous pages, use > > > * folio_try_dup_anon_rmap_*() and split if duplicating fails. > > > */ > > > - pudp_set_wrprotect(src_mm, addr, src_pud); > > > - pud = pud_mkold(pud_wrprotect(pud)); > > > + if (is_cow_mapping(vma->vm_flags) && pud_write(pud)) { > > > + pudp_set_wrprotect(src_mm, addr, src_pud); > > > + pud = pud_wrprotect(pud); > > > + } > > Do we need the logic to clear dirty bit in the child as that in > > __copy_present_ptes()? (and also for the pmd's case). > > > > e.g. > > if (vma->vm_flags & VM_SHARED) > > pud = pud_mkclean(pud); > > Yeah, good question. I remember I thought about that when initially > working on these lines, but I forgot the details, or maybe I simply tried > to stick with the current code base, as the dirty bit used to be kept even > in the child here. > > I'd expect there's only performance differences, but still sounds like I'd > better leave that to whoever knows the best on the implications, then draft > it as a separate patch but only when needed. Sorry, but this vaguensss simply leaves me with nowhere to go. I'll drop the series - let's revisit after -rc1 please.