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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 Subject: Re: [PATCH v2 0/5] add static PMD zero page support Message-ID: References: <20250707142319.319642-1-kernel@pankajraghav.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Stat-Signature: 6spbugb5937rojaosjd5enptphxr6hwx X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 9DAEEC000F X-Rspam-User: X-HE-Tag: 1752593149-235465 X-HE-Meta: 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 ax33IhJ6 beMcnFCpGmXDMZXtj1Vw+Q5GnCpZl9frWqqTbw0+u+DGbhwtWz9E1qDDxR1oD3aiwAtN5P0L2hOeUePuOL/G8IFOjEesm/qRkzjetyTaBdgXmjJK9310n4m87Yp2/M4aBe+8MPSWbaFW4NBYYx1UxEIZhHIftij/ZFyLeVOTDozOxTl8n7sKF0EQer11tfEQ2eqysVtSekJcrztAr0G7iRlYrdO05OoHlebmBfxcrlV9Qk5KMJ3OMrU3QRLOXyVtqcPZ49I0mXLf0re2XnDfwYkkyhw+HbXZFkA29IaTuNm6hm905AX29NFvT9Ep8D+ehQ/D1Ob2AsBLbCfTVV+zAJjHk8oLVQDDwmRm1M9tSnZ1VZJJm/mPQ3v78G8MXhWD65V6gBdeM9guLfyWkHnVyVDAufw== 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, Jul 15, 2025 at 04:16:44PM +0200, David Hildenbrand wrote: > 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. Actually I had something similar in one of my earlier versions[1] where we can opt in from arch specific Kconfig with *WANT* instead *HAS*. For starters, I will enable this only from x86. We can probably extend this once we get the base patches up. [1] https://lore.kernel.org/linux-mm/20250522090243.758943-2-p.raghav@samsung.com/ -- Pankaj