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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 Cc: "Vishal Moola (Oracle)" , Andrew Morton , Matthew Wilcox , linux-mm@kvack.org, linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-csky@vger.kernel.org, linux-hexagon@vger.kernel.org, loongarch@lists.linux.dev, linux-m68k@lists.linux-m68k.org, linux-mips@vger.kernel.org, linux-openrisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, linux-sh@vger.kernel.org, sparclinux@vger.kernel.org, linux-um@lists.infradead.org, xen-devel@lists.xenproject.org, kvm@vger.kernel.org, Catalin Marinas , Huacai Chen , Geert Uytterhoeven , Thomas Bogendoerfer , Dinh Nguyen , Jonas Bonn , Claudio Imbrenda , Paul Walmsley , "David S. Miller" , Richard Weinberger , Yoshinori Sato , Dave Hansen , Arnd Bergmann , Christophe Leroy 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-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 0AF211C0004 X-Stat-Signature: mdfbt3msi8esaw6cog41mn971tmnbip4 X-Rspam-User: X-HE-Tag: 1687938086-344673 X-HE-Meta: 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 WfsK6aUq 2qDRG/WJzlpXCiWuwvNRWQ/4liBq9ihB2fjXpPL+WhJ+9a3gmWPhgMisie0vYGvizn2Hx6Hln6LlQmeSOsP338Wn1RCDb3tcE4kYcSWka754swTpZ6Tjr+WTTbGT0pUTuG9mI6vw3tZaMot1/mDmHjC3iDW2qxD66+qLTH/0Fnyxl31Y0pX8fJnACc4jEPs1dhIRsEMtRBeeOeRkiLsvPYI3qQtPkH1uIgTar2oWRGL6hwHyJy7xwZCVNeOMOUG4fzHydNJJEJxbkdM/kS6gM3px36lEQLhoqEkfO2jq09+TE4VGvfHHdjS1j98+CAihx/68ij5EZ/tQf4nupUFDaYNvh3CTUb4LZSSv11YgoGRdvRZQuYnY13gcNYaD+Pd3xsyHzz9bsYxf/IcGsacVoEau6S0LPBqX0tnQl3OktlTTPir2R+/zCw/26rMOvCx4uHkkRMM+AqQUaVII= 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: 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