From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 43227EE49AB for ; Tue, 22 Aug 2023 18:47:08 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id C50DE280059; Tue, 22 Aug 2023 14:47:07 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id BDA0D280040; Tue, 22 Aug 2023 14:47:07 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id A536E280059; Tue, 22 Aug 2023 14:47:07 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0015.hostedemail.com [216.40.44.15]) by kanga.kvack.org (Postfix) with ESMTP id 92948280040 for ; Tue, 22 Aug 2023 14:47:07 -0400 (EDT) Received: from smtpin01.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay07.hostedemail.com (Postfix) with ESMTP id EA547160459 for ; Tue, 22 Aug 2023 18:47:06 +0000 (UTC) X-FDA: 81152622852.01.544C0C0 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) by imf29.hostedemail.com (Postfix) with ESMTP id ECC47120018 for ; Tue, 22 Aug 2023 18:47:04 +0000 (UTC) Authentication-Results: imf29.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b="RAzY/3Fm"; dmarc=none; spf=none (imf29.hostedemail.com: domain of willy@infradead.org has no SPF policy when checking 90.155.50.34) smtp.mailfrom=willy@infradead.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1692730025; 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:dkim-signature; bh=J31tX1IjpfiCQxayR49GQoOflBRKi40HTvUBqvNFOZY=; b=Wvli35dG4tnOxlVluKGA7eNM5629Afh9D6/YoyFjaKPF+oAmD/UdvY8iZWMT7BXB0pXtWR yJOOMPBSKVAKWThBuLljJw/9fMKD2Y+Y2qYrFIG+ezFI/TJODOJYFs33t9vrgNbpDzUCz7 8EyGDJGWUraTZGuFNF/sQ29Ti7uB6kI= ARC-Authentication-Results: i=1; imf29.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b="RAzY/3Fm"; dmarc=none; spf=none (imf29.hostedemail.com: domain of willy@infradead.org has no SPF policy when checking 90.155.50.34) smtp.mailfrom=willy@infradead.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1692730025; a=rsa-sha256; cv=none; b=0FXOsnZb51Wq6NkHXE/pHRzRqIsPuNVzHnvehrk4l8mGu/IkU+pMkpeBznkvR8QkDTgids bI9riw7k/Bhz8AiNj3AoFnIUHCIKVhlsaBwf4qHbNXCvzuyzolr1ZMhaF9oaoYRPQtvBli FeQQT3H4NLJja9rFic6rcB5RIF2A3rs= DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=J31tX1IjpfiCQxayR49GQoOflBRKi40HTvUBqvNFOZY=; b=RAzY/3FmhkOeez9WRyFLLv4ZSq U9rG0oMX7UlPyR/D8x7L4mEEOPnVmJVv72dkSFxz3K3fx+HJjz0yoyeOk1QTD4Bln2OjioJ+WG3UG CnjPXzmOixxB/77VgttDEjTQVN+QS8gKeI40gmVskiO5EQQ7Den2j/G96cP6WVrEfYYyC+vujh8og eJ/TUp3RaxHtDOKFUHYAODkAttL76BNxIck57m/l5uS1N1aQ2ZPhNzqFsS9g+ZZtgp8Bjfnnp5VzH Sh7M7AqyItqQzyxp6n+/g33j9JDbH/tinn2kkkuSh0EOjzNT3lsO7aLfQFQIinDdpU3s/xpPYqKx1 u14eK8IA==; Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1qYWNp-000KO8-5r; Tue, 22 Aug 2023 18:45:41 +0000 Date: Tue, 22 Aug 2023 19:45:41 +0100 From: Matthew Wilcox To: Hugh Dickins Cc: Peter Xu , Jann Horn , Andrew Morton , Mike Kravetz , Mike Rapoport , "Kirill A. Shutemov" , David Hildenbrand , Suren Baghdasaryan , Qi Zheng , Yang Shi , Mel Gorman , Peter Zijlstra , Will Deacon , Yu Zhao , Alistair Popple , Ralph Campbell , Ira Weiny , Steven Price , SeongJae Park , Lorenzo Stoakes , Huang Ying , Naoya Horiguchi , Christophe Leroy , Zack Rusin , Jason Gunthorpe , Axel Rasmussen , Anshuman Khandual , Pasha Tatashin , Miaohe Lin , Minchan Kim , Christoph Hellwig , Song Liu , Thomas Hellstrom , Russell King , "David S. Miller" , Michael Ellerman , "Aneesh Kumar K.V" , Heiko Carstens , Christian Borntraeger , Claudio Imbrenda , Alexander Gordeev , Gerald Schaefer , Vasily Gorbik , Vishal Moola , Vlastimil Babka , Zi Yan , Zach O'Keefe , Linux ARM , sparclinux@vger.kernel.org, linuxppc-dev , linux-s390 , kernel list , Linux-MM Subject: Re: [PATCH mm-unstable] mm/khugepaged: fix collapse_pte_mapped_thp() versus uffd Message-ID: References: <4d31abf5-56c0-9f3d-d12f-c9317936691@google.com> <1b7c7056-d742-86bf-fec-fdb024b2381@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1b7c7056-d742-86bf-fec-fdb024b2381@google.com> X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: ECC47120018 X-Stat-Signature: mrkcs7fipthojm5gdo8u9qwuntsm1935 X-Rspam-User: X-HE-Tag: 1692730024-578954 X-HE-Meta: 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 jEikpiBx EzKjyBD68xxLarL2ENUg72mRHVeR8cSpjiDlKpjdrCRcZqUwQix67HXeeVSyb2hfqg7t3yb0Fagv+HagsZ/2h1MNYV4tfTg9UUnMjVErMits5ebdyyp9x7EZoqqGQKO89OVCnkemQI9USjWqTk8K4gohUGdHrU2AAUj72BaOuJWMjVoinmuM7B9tRgs5rR/a2tKA7ovrnS6YuR9eC4c189G8i9X6J3Rys4Z/yLdG/RvgGGtoqL4emszdJvJyFQ3/Prv+1 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 Tue, Aug 22, 2023 at 11:34:19AM -0700, Hugh Dickins wrote: > (Yes, the locking is a bit confusing: but mainly for the unrelated reason, > that with the split locking configs, we never quite know whether this lock > is the same as that lock or not, and so have to be rather careful.) Is it time to remove the PTE split locking config option? I believe all supported architectures have at least two levels of page tables, so if we have split ptlocks, ptl and pml are always different from each other (it's just that on two level machines, pmd == pud == p4d == pgd). With huge thread counts now being the norm, it's hard to see why anybody would want to support SMP and !SPLIT_PTE_PTLOCKS. To quote the documentation ... Split page table lock for PTE tables is enabled compile-time if CONFIG_SPLIT_PTLOCK_CPUS (usually 4) is less or equal to NR_CPUS. If split lock is disabled, all tables are guarded by mm->page_table_lock. You can barely buy a wrist-watch without eight CPUs these days.