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 X-Spam-Level: X-Spam-Status: No, score=-5.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id E83F0C35257 for ; Mon, 12 Oct 2020 19:54:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id AFD1D2087E for ; Mon, 12 Oct 2020 19:54:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730538AbgJLTx6 (ORCPT ); Mon, 12 Oct 2020 15:53:58 -0400 Received: from mga09.intel.com ([134.134.136.24]:29002 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726676AbgJLTx5 (ORCPT ); Mon, 12 Oct 2020 15:53:57 -0400 IronPort-SDR: sHEBSwDrhTzQU2S1NEllE7XlTU+xF+PhbrOIMhK+ymP1xuGREJ/BLRLAOafpJKPLRy0iKRj28m +ZZbJv87UD9w== X-IronPort-AV: E=McAfee;i="6000,8403,9772"; a="165907662" X-IronPort-AV: E=Sophos;i="5.77,367,1596524400"; d="scan'208";a="165907662" X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga005.jf.intel.com ([10.7.209.41]) by orsmga102.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 12 Oct 2020 12:53:55 -0700 IronPort-SDR: fkO3cV1AstS50IlWJFeIR7IMIWTUvxOVu0RxBH9tBAb2aFjzmjvlioAsa4gAQcEu3X0zxNtHVX KqidbmrXoAPg== X-IronPort-AV: E=Sophos;i="5.77,367,1596524400"; d="scan'208";a="530096227" Received: from iweiny-desk2.sc.intel.com (HELO localhost) ([10.3.52.147]) by orsmga005-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 12 Oct 2020 12:53:54 -0700 Date: Mon, 12 Oct 2020 12:53:54 -0700 From: Ira Weiny To: Matthew Wilcox Cc: Dave Hansen , Eric Biggers , Andrew Morton , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Andy Lutomirski , Peter Zijlstra , linux-aio@kvack.org, linux-efi@vger.kernel.org, kvm@vger.kernel.org, linux-doc@vger.kernel.org, linux-mmc@vger.kernel.org, Dave Hansen , dri-devel@lists.freedesktop.org, linux-mm@kvack.org, target-devel@vger.kernel.org, linux-mtd@lists.infradead.org, linux-kselftest@vger.kernel.org, samba-technical@lists.samba.org, ceph-devel@vger.kernel.org, drbd-dev@lists.linbit.com, devel@driverdev.osuosl.org, linux-cifs@vger.kernel.org, linux-nilfs@vger.kernel.org, linux-scsi@vger.kernel.org, linux-nvdimm@lists.01.org, linux-rdma@vger.kernel.org, x86@kernel.org, amd-gfx@lists.freedesktop.org, linux-afs@lists.infradead.org, cluster-devel@redhat.com, linux-cachefs@redhat.com, intel-wired-lan@lists.osuosl.org, xen-devel@lists.xenproject.org, linux-ext4@vger.kernel.org, Fenghua Yu , ecryptfs@vger.kernel.org, linux-um@lists.infradead.org, intel-gfx@lists.freedesktop.org, linux-erofs@lists.ozlabs.org, reiserfs-devel@vger.kernel.org, linux-block@vger.kernel.org, linux-bcache@vger.kernel.org, Jaegeuk Kim , Dan Williams , io-uring@vger.kernel.org, linux-nfs@vger.kernel.org, linux-ntfs-dev@lists.sourceforge.net, netdev@vger.kernel.org, kexec@lists.infradead.org, linux-kernel@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, linux-fsdevel@vger.kernel.org, bpf@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-btrfs@vger.kernel.org Subject: Re: [PATCH RFC PKS/PMEM 22/58] fs/f2fs: Utilize new kmap_thread() Message-ID: <20201012195354.GC2046448@iweiny-DESK2.sc.intel.com> References: <20201009195033.3208459-1-ira.weiny@intel.com> <20201009195033.3208459-23-ira.weiny@intel.com> <20201009213434.GA839@sol.localdomain> <20201010003954.GW20115@casper.infradead.org> <20201010013036.GD1122@sol.localdomain> <20201012065635.GB2046448@iweiny-DESK2.sc.intel.com> <20201012161946.GA858@sol.localdomain> <5d621db9-23d4-e140-45eb-d7fca2093d2b@intel.com> <20201012164438.GA20115@casper.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201012164438.GA20115@casper.infradead.org> User-Agent: Mutt/1.11.1 (2018-12-01) Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On Mon, Oct 12, 2020 at 05:44:38PM +0100, Matthew Wilcox wrote: > On Mon, Oct 12, 2020 at 09:28:29AM -0700, Dave Hansen wrote: > > kmap_atomic() is always preferred over kmap()/kmap_thread(). > > kmap_atomic() is _much_ more lightweight since its TLB invalidation is > > always CPU-local and never broadcast. > > > > So, basically, unless you *must* sleep while the mapping is in place, > > kmap_atomic() is preferred. > > But kmap_atomic() disables preemption, so the _ideal_ interface would map > it only locally, then on preemption make it global. I don't even know > if that _can_ be done. But this email makes it seem like kmap_atomic() > has no downsides. And that is IIUC what Thomas was trying to solve. Also, Linus brought up that kmap_atomic() has quirks in nesting.[1] >From what I can see all of these discussions support the need to have something between kmap() and kmap_atomic(). However, the reason behind converting call sites to kmap_thread() are different between Thomas' patch set and mine. Both require more kmap granularity. However, they do so with different reasons and underlying implementations but with the _same_ resulting semantics; a thread local mapping which is preemptable.[2] Therefore they each focus on changing different call sites. While this patch set is huge I think it serves a valuable purpose to identify a large number of call sites which are candidates for this new semantic. Ira [1] https://lore.kernel.org/lkml/CAHk-=wgbmwsTOKs23Z=71EBTrULoeaH2U3TNqT2atHEWvkBKdw@mail.gmail.com/ [2] It is important to note these implementations are not incompatible with each other. So I don't see yet another 'kmap_something()' being required.