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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1D029CDB483 for ; Thu, 19 Oct 2023 19:53:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1346533AbjJSTx4 (ORCPT ); Thu, 19 Oct 2023 15:53:56 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48806 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1346551AbjJSTxy (ORCPT ); Thu, 19 Oct 2023 15:53:54 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 63F3EFA for ; Thu, 19 Oct 2023 12:53:06 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1697745185; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=xsesIdim+wPTdU/RUNRWHqvYIZjYuIVW1UPJdK5PEjw=; b=ZWruexABPn1xnioa8tXDoYsxb+yBu8lLypHsouNe2F81i7AL0+1nNB5dIUTvZlou/rxl+Q pSdmg9+FQcpsd3UXD7fOWwnxWNHcWvwuL9yJgPKWgdfFMmh3x6hzNLgeKsYM5SJfYkYcfs G2tFFWKXHV0kExhHLT7foOAEhiuwob0= Received: from mail-qk1-f199.google.com (mail-qk1-f199.google.com [209.85.222.199]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-581-mocXLl-6PZGcnYvinsIuaQ-1; Thu, 19 Oct 2023 15:53:04 -0400 X-MC-Unique: mocXLl-6PZGcnYvinsIuaQ-1 Received: by mail-qk1-f199.google.com with SMTP id af79cd13be357-77891ef5fc9so489685a.1 for ; Thu, 19 Oct 2023 12:53:04 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1697745183; x=1698349983; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=xsesIdim+wPTdU/RUNRWHqvYIZjYuIVW1UPJdK5PEjw=; b=kaU1hbtQhKbnjqzPRThbTHdH+hZaOZ4LXBcHMplZK9FyZm2HiLeX1KwLw2rw7dt4Xf BjizcHC/FIHZ8/C098pyJIuWSm3ZstvZghsisEkDFE835R17qNClBXB1VQ4CZQn0JBg9 iujQHdb7Fugl8wPk3RbOiRXms6XwFPNLWct0m0QjA7sVeySZBBGgRj0Ju8oN10Khrhgf 2Tx9EdKxynA7PkTBilLyvxd4llovEofk6Sj14ckZFtXbtEauPNI49QBiUmcM2b+J4fFb +Pb3jl49YibLxLEmc0QIzZ9tAzF9xgHtYDElxWhtx0Rh0eJk3pfzzl/yVr8Q2Q7zDnya Q4Lg== X-Gm-Message-State: AOJu0Yy8jooji9uDYZ6UHuOXvjyL7knnMHxXKRvdYMbZbHIpQSATqxX0 KYgDxZWeY9xnIXBpJQgXS9JnOT+qmKg5J8QcTaDk8AEy6SBLgYnSrioMJM0L2A/nQ4g/MaWd6Z8 ++kb6VG/ybO+aAoca1493v/41 X-Received: by 2002:a05:620a:1a87:b0:778:96e8:90af with SMTP id bl7-20020a05620a1a8700b0077896e890afmr3341461qkb.5.1697745183641; Thu, 19 Oct 2023 12:53:03 -0700 (PDT) X-Google-Smtp-Source: AGHT+IE6lM3hjpOvbZ85Uma0UlRsQCBxfq3qPNAwSumdJHciqDnKFJqXdgnennQ8IWt6btGoUMNwrQ== X-Received: by 2002:a05:620a:1a87:b0:778:96e8:90af with SMTP id bl7-20020a05620a1a8700b0077896e890afmr3341429qkb.5.1697745183351; Thu, 19 Oct 2023 12:53:03 -0700 (PDT) Received: from x1n (cpe5c7695f3aee0-cm5c7695f3aede.cpe.net.cable.rogers.com. [99.254.144.39]) by smtp.gmail.com with ESMTPSA id 2-20020a05620a070200b0077413b342e9sm53812qkc.128.2023.10.19.12.53.01 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 19 Oct 2023 12:53:03 -0700 (PDT) Date: Thu, 19 Oct 2023 15:53:01 -0400 From: Peter Xu To: David Hildenbrand Cc: Lokesh Gidra , Suren Baghdasaryan , akpm@linux-foundation.org, viro@zeniv.linux.org.uk, brauner@kernel.org, shuah@kernel.org, aarcange@redhat.com, hughd@google.com, mhocko@suse.com, axelrasmussen@google.com, rppt@kernel.org, willy@infradead.org, Liam.Howlett@oracle.com, jannh@google.com, zhangpeng362@huawei.com, bgeffon@google.com, kaleshsingh@google.com, ngeoffray@google.com, jdduke@google.com, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, kernel-team@android.com Subject: Re: [PATCH v3 2/3] userfaultfd: UFFDIO_MOVE uABI Message-ID: References: <478697aa-f55c-375a-6888-3abb343c6d9d@redhat.com> <205abf01-9699-ff1c-3e4e-621913ada64e@redhat.com> <12588295-2616-eb11-43d2-96a3c62bd181@redhat.com> <8d187891-f131-4912-82d8-13112125b210@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Oct 19, 2023 at 05:41:01PM +0200, David Hildenbrand wrote: > That's not my main point. It can easily become a maintenance burden without > any real use cases yet that we are willing to support. That's why I requested a few times that we can discuss the complexity of cross-mm support already here, and I'm all ears if I missed something on the "maintenance burden" part.. I started by listing what I think might be different, and we can easily speedup single-mm with things like "if (ctx->mm != mm)" checks with e.g. memcg, just like what this patch already did with pgtable depositions. We keep saying "maintenance burden" but we refuse to discuss what is that.. I'll leave that to Suren and Lokesh to decide. For me the worst case is one more flag which might be confusing, which is not the end of the world.. Suren, you may need to work more thoroughly to remove cross-mm implications if so, just like when renaming REMAP to MOVE. Thanks, -- Peter Xu