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[46.138.191.2]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-6a59dd550bcsm13565742a12.0.2026.08.25.02.08.41 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 25 Aug 2026 02:08:42 -0700 (PDT) From: Artem Lytkin To: David Hildenbrand , Matthew Wilcox Cc: Ackerley Tng , Zi Yan , Kiryl Shutsemau , Hugh Dickins , Baolin Wang , linux-mm@kvack.org, linux-fsdevel@vger.kernel.org Subject: Re: [RFC PATCH 0/4] Extend xas_split* to support splitting arbitrarily large entries Date: Tue, 25 Aug 2026 12:08:27 +0300 Message-ID: <20260825090827.64550-1-iprintercanon@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: References: <20251117224701.1279139-1-ackerleytng@google.com> <20260824194755.216000-1-iprintercanon@gmail.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Stat-Signature: eqy91s159zbpfhxazxs36gpkx41psgth X-Rspamd-Queue-Id: 6D43640009 X-Rspam-User: X-Rspamd-Server: rspam12 X-HE-Tag: 1787648924-846778 X-HE-Meta: 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 p21pRvoy 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Aug 25, 2026 at 10:31:34AM +0200, David Hildenbrand (Arm) wrote: > > IOW is this driven by a real need, or just some completionist thing? > > I heard some use cases using 512M THPs on arm64 to back VMs, but it's mostly > anon pages, and not really ordinary pagecache. No real need on my side. I took the pagemap.h comment and the selftest skips as an invitation, and the one 64K user I can find on the list (Meta, in Kiryl's collapse RFC) says mTHP is what they want. Dropping the arm64 angle. > But a buddy-like split is clearly preferable. (or avoiding splitting in the > first place :) ) That path exists as xas_try_split(). What's left is the uniform split to order 0 that __folio_split() still does through xas_split_alloc(), and the only one asking for it past order 11 is guest_memfd. That's Ackerley's call; if he wants the rebase I'll do the mechanical part. Artem