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(p200300d82f2849002c244e201f219fbd.dip0.t-ipconnect.de. [2003:d8:2f28:4900:2c24:4e20:1f21:9fbd]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3b5e8bd1a2bsm15527533f8f.14.2025.07.15.07.16.44 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 15 Jul 2025 07:16:46 -0700 (PDT) Message-ID: Date: Tue, 15 Jul 2025 16:16:44 +0200 Precedence: bulk X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 0/5] add static PMD zero page support To: Lorenzo Stoakes Cc: Pankaj Raghav , Zi Yan , Suren Baghdasaryan , Ryan Roberts , Baolin Wang , Borislav Petkov , Ingo Molnar , "H . Peter Anvin" , Vlastimil Babka , Mike Rapoport , Dave Hansen , Michal Hocko , Andrew Morton , Thomas Gleixner , Nico Pache , Dev Jain , "Liam R . Howlett" , Jens Axboe , linux-kernel@vger.kernel.org, willy@infradead.org, linux-mm@kvack.org, x86@kernel.org, linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org, "Darrick J . Wong" , mcgrof@kernel.org, gost.dev@samsung.com, hch@lst.de, Pankaj Raghav References: <20250707142319.319642-1-kernel@pankajraghav.com> From: David Hildenbrand Content-Language: en-US Organization: Red Hat In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 15.07.25 16:12, Lorenzo Stoakes wrote: > On Tue, Jul 15, 2025 at 04:06:29PM +0200, David Hildenbrand wrote: >> I think at some point we discussed "when does the PMD-sized zeropage make >> *any* sense on these weird arch configs" (512MiB on arm64 64bit) >> >> No idea who wants to waste half a gig on that at runtime either. > > Yeah this is a problem we _really_ need to solve. But obviously somewhat out of > scope here. > >> >> But yeah, we should let the arch code opt in whether it wants it or not (in >> particular, maybe only on arm64 with CONFIG_PAGE_SIZE_4K) > > I don't think this should be an ARCH_HAS_xxx. > > Because that's saying 'this architecture has X', this isn't architecture > scope. > > I suppose PMDs may vary in terms of how huge they are regardless of page > table size actually. > > So maybe the best solution is a semantic one - just rename this to > ARCH_WANT_STATIC_PMD_ZERO_PAGE > > And then put the page size selector in the arch code. > > For example in arm64 we have: > > select ARCH_WANT_HUGE_PMD_SHARE if ARM64_4K_PAGES || (ARM64_16K_PAGES && !ARM64_VA_BITS_36) > > So doing something similar here like: > > select ARCH_WANT_STATIC_PMD_ZERO_PAGE if ARM64_4K_PAGES > > Would do thie job and sort everything out. Yes. -- Cheers, David / dhildenb