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[2003:cb:c715:ef00:fa40:f6df:a68d:a0e4]) by smtp.gmail.com with ESMTPSA id hn10-20020a05600ca38a00b003fba586100fsm3970092wmb.6.2023.06.28.00.41.18 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 28 Jun 2023 00:41:20 -0700 (PDT) Message-ID: <26282cb8-b6b0-f3a0-e82d-b4fec45c5f72@redhat.com> Date: Wed, 28 Jun 2023 09:41:18 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.12.0 To: Hugh Dickins References: <20230627031431.29653-1-vishal.moola@gmail.com> <90e643ca-de72-2f4c-f4fe-35e06e1a9277@google.com> From: David Hildenbrand Organization: Red Hat Subject: Re: [PATCH v6 00/33] Split ptdesc from struct page In-Reply-To: <90e643ca-de72-2f4c-f4fe-35e06e1a9277@google.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed 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: kvm@vger.kernel.org, linux-sh@vger.kernel.org, Catalin Marinas , Dave Hansen , linux-openrisc@vger.kernel.org, linux-csky@vger.kernel.org, sparclinux@vger.kernel.org, linux-riscv@lists.infradead.org, Claudio Imbrenda , linux-arch@vger.kernel.org, linux-s390@vger.kernel.org, Yoshinori Sato , linux-hexagon@vger.kernel.org, Huacai Chen , Matthew Wilcox , Geert Uytterhoeven , xen-devel@lists.xenproject.org, Jonas Bonn , Arnd Bergmann , linux-um@lists.infradead.org, linux-m68k@lists.linux-m68k.org, loongarch@lists.linux.dev, Paul Walmsley , linux-arm-kernel@lists.infradead.org, Thomas Bogendoerfer , linux-mm@kvack.org, linux-mips@vger.kernel.org, "Vishal Moola \(Oracle\)" , Dinh Nguyen , Richard Weinberger , Andrew Morton , linuxppc-dev@lists.ozlabs.org, "David S. Miller" Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On 27.06.23 22:13, Hugh Dickins wrote: > On Tue, 27 Jun 2023, David Hildenbrand wrote: >> On 27.06.23 06:44, Hugh Dickins wrote: >>> On Mon, 26 Jun 2023, Vishal Moola (Oracle) wrote: >>> >>>> The MM subsystem is trying to shrink struct page. This patchset >>>> introduces a memory descriptor for page table tracking - struct ptdesc. >>> ... >>>> 39 files changed, 686 insertions(+), 455 deletions(-) >>> >>> I don't see the point of this patchset: to me it is just obfuscation of >>> the present-day tight relationship between page table and struct page. >>> >>> Matthew already explained: >>> >>>> The intent is to get ptdescs to be dynamically allocated at some point >>>> in the ~2-3 years out future when we have finished the folio project ... >>> >>> So in a kindly mood, I'd say that this patchset is ahead of its time. >>> But I can certainly adapt to it, if everyone else sees some point to it. >> >> I share your thoughts, that code churn which will help eventually in the far, >> far future (not wanting to sound too pessimistic, but it's not going to be >> there tomorrow ;) ). >> >> However, if it's just the same as the other conversions we already did (e.g., >> struct slab), then I guess there is no reason to stop now -- the obfuscation >> already happened. >> >> ... or is there a difference regarding this conversion and the previous ones? > > I was aware of the struct slab thing, didn't see much point there myself > either; but it was welcomed by Vlastimil, and barely affected outside of > slab allocators, so I had no reason to object. > > You think that if a little unnecessary churn (a *lot* of churn if you > include folios, which did save some repeated calls to compound_head()) > has already occurred, that's a good precedent for allowing more and more? Well, if you phrase it like that ... no, I'm not in favor of unnecessary churn at all. Yes, folios were/are a lot of churn (IMHO not unnecessary, though). I'm not a friend of these "overlays"; it all only really makes sense to me once we actually allocate the descriptors dynamically. Maybe some of the existing/ongoing conversions were different (that's why I was asking for the difference, as you said the "struct slab" thing was well received). If they are primarily only unnecessary churn for now (and unclear when/how it will become useful), I share your opinion. -- Cheers, David / dhildenb