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c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1744016391; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=NE/ulqoa33Xs5DbV1pC6Y5lYyaE69CKfz1Bp0kDs8lo=; b=04ih628yEFcTyzl83YRtwE3cp5vmZufLn1WYyYTaGqFCjbzCdABgOoH9Mmv+6BA4NAJsex wAdYs/CMHReN/OWVXI1qZLguRJNu23iPxqctQ6sakzrSCnHrstFk/i3qrQ1ftlSxwsjAcj Cf87bgPS1MbcTd6a+cHioq79oehJvZU= Received: by verein.lst.de (Postfix, from userid 2407) id 2DB0768BFE; Mon, 7 Apr 2025 10:59:44 +0200 (CEST) Date: Mon, 7 Apr 2025 10:59:44 +0200 From: Christoph Hellwig To: Muchun Song Cc: Huan Yang , bingbu.cao@linux.intel.com, Christoph Hellwig , Matthew Wilcox , Gerd Hoffmann , Vivek Kasireddy , Sumit Semwal , Christian =?iso-8859-1?Q?K=F6nig?= , Andrew Morton , Uladzislau Rezki , Shuah Khan , linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-media@vger.kernel.org, linaro-mm-sig@lists.linaro.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org, opensource.kernel@vivo.com Subject: Re: CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP is broken, was Re: [RFC PATCH 0/6] Deep talk about folio vmap Message-ID: <20250407085943.GA27481@lst.de> References: <20250327092922.536-1-link@vivo.com> <20250404090111.GB11105@lst.de> <9A899641-BDED-4773-B349-56AF1DD58B21@linux.dev> <43DD699A-5C5D-429B-A2B5-61FBEAE2E252@linux.dev> <6f76a497-248b-4f92-9448-755006c732c8@vivo.com> <35D26C00-952F-481C-8345-E339F0ED770B@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <35D26C00-952F-481C-8345-E339F0ED770B@linux.dev> User-Agent: Mutt/1.5.17 (2007-11-01) X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 6E3E5160005 X-Stat-Signature: r5md79oydckm36cowft1bm6mf9xubdaj X-Rspam-User: X-HE-Tag: 1744016391-597131 X-HE-Meta: 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 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 Mon, Apr 07, 2025 at 02:43:20PM +0800, Muchun Song wrote: > By the way, in case you truly struggle to comprehend the fundamental > aspects of HVO, I would like to summarize for you the user-visible > behaviors in comparison to the situation where HVO is disabled. > > HVO Status Tail Page Structures Head Page Structures > Enabled Read-Only (RO) Read-Write (RW) > Disabled Read-Write (RW) Read-Write (RW) > > The sole distinction between the two scenarios lies in whether the > tail page structures are allowed to be written or not. Please refrain > from getting bogged down in the details of the implementation of HVO. This feels extremely fragile to me. I doubt many people know what operations needs read vs write access to tail pages. Or for higher level operations if needs access to tail pages at all.