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[172.10.233.147]) by smtp.gmail.com with ESMTPSA id q131-20020a817589000000b00565eb8af1fesm1991442ywc.132.2023.06.27.13.13.56 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 27 Jun 2023 13:13:59 -0700 (PDT) Date: Tue, 27 Jun 2023 13:13:49 -0700 (PDT) From: Hugh Dickins X-X-Sender: hugh@ripple.attlocal.net To: David Hildenbrand Subject: Re: [PATCH v6 00/33] Split ptdesc from struct page In-Reply-To: Message-ID: <90e643ca-de72-2f4c-f4fe-35e06e1a9277@google.com> References: <20230627031431.29653-1-vishal.moola@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII 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 , Hugh Dickins , 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 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? My opinion happens to differ on that. Hugh