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<20200922050314.GB12096@dread.disaster.area> <20200922172553.GL32101@casper.infradead.org> User-Agent: Alpine 2.02 (LRH 1266 2009-07-14) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Message-ID-Hash: QULKWWZVVSUXMLHAW3WJQUX6YTFYCNBH X-Message-ID-Hash: QULKWWZVVSUXMLHAW3WJQUX6YTFYCNBH X-MailFrom: mpatocka@redhat.com X-Mailman-Rule-Hits: nonmember-moderation X-Mailman-Rule-Misses: dmarc-mitigation; no-senders; approved; emergency; loop; banned-address; member-moderation CC: Dave Chinner , Linus Torvalds , Alexander Viro , Andrew Morton , Jan Kara , Eric Sandeen , Dave Chinner , "Tadakamadla, Rajesh (DCIG/CDI/HPS Perf)" , Linux Kernel Mailing List , linux-fsdevel , linux-nvdimm X-Mailman-Version: 3.1.1 Precedence: list List-Id: "Linux-nvdimm developer list." Archived-At: List-Archive: List-Help: List-Post: List-Subscribe: List-Unsubscribe: Content-Type: TEXT/PLAIN; charset="us-ascii" Content-Transfer-Encoding: 7bit On Tue, 22 Sep 2020, Matthew Wilcox wrote: > > > The NVFS indirect block tree has a fan-out of 16, > > > > No. The top level in the inode contains 16 blocks (11 direct and 5 > > indirect). And each indirect block can have 512 pointers (4096/8). You can > > format the device with larger block size and this increases the fanout > > (the NVFS block size must be greater or equal than the system page size). > > > > 2 levels can map 1GiB (4096*512^2), 3 levels can map 512 GiB, 4 levels can > > map 256 TiB and 5 levels can map 128 PiB. > > But compare to an unfragmented file ... you can map the entire thing with > a single entry. Even if you have to use a leaf node, you can get four > extents in a single cacheline (and that's a fairly naive leaf node layout; > I don't know exactly what XFS uses) But the benchmarks show that it is comparable to extent-based filesystems. > > > Rename is another operation that has specific "operation has atomic > > > behaviour" expectations. I haven't looked at how you've > > > implementated that yet, but I suspect it also is extremely difficult > > > to implement in an atomic manner using direct pmem updates to the > > > directory structures. > > > > There is a small window when renamed inode is neither in source nor in > > target directory. Fsck will reclaim such inode and add it to lost+found - > > just like on EXT2. > > ... ouch. If you have to choose, it'd be better to link it to the second > directory then unlink it from the first one. Then your fsck can detect > it has the wrong count and fix up the count (ie link it into both > directories rather than neither). I admit that this is lame and I'll fix it. Rename is not so performance-critical, so I can add a small journal for this. > > If you think that the lack of journaling is show-stopper, I can implement > > it. But then, I'll have something that has complexity of EXT4 and > > performance of EXT4. So that there will no longer be any reason why to use > > NVFS over EXT4. Without journaling, it will be faster than EXT4 and it may > > attract some users who want good performance and who don't care about GID > > and UID being updated atomically, etc. > > Well, what's your intent with nvfs? Do you already have customers in mind > who want to use this in production, or is this somewhere to play with and > develop concepts that might make it into one of the longer-established > filesystems? I develop it just because I thought it may be interesting. So far, it doesn't have any serious users (the physical format is still changing). I hope that it could be useable as a general purpose root filesystem when Optane DIMMs become common. Mikulas _______________________________________________ Linux-nvdimm mailing list -- linux-nvdimm@lists.01.org To unsubscribe send an email to linux-nvdimm-leave@lists.01.org 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=-6.6 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,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 CE5DAC4363D for ; Thu, 24 Sep 2020 15:00:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 74E062074B for ; Thu, 24 Sep 2020 15:00:34 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="T6OTWQhH" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728531AbgIXPAd (ORCPT ); Thu, 24 Sep 2020 11:00:33 -0400 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:60688 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728277AbgIXPAc (ORCPT ); Thu, 24 Sep 2020 11:00:32 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1600959630; 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=6ZooZd+2Abb0NioOnlAqnGdn71WL8pkXeAG+ycQqMKg=; b=T6OTWQhHoTLWPLIqDyyoJpMVBlK1cfPbFvGdzSoW1mzB/Bsr9PyFStcVLqztYuo80CDI0j cfSNARpB3TOmOagvvQ8G6KMCr2CsRMSVU0xe7KF/86rzP1J5WALHW+7k86Fl+pZrlfGBjr pEhyZiGK2kBVCUZFcdXcmJWQH1ChE6M= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-250-lTQRB-_VPU2rFBtOwp75YA-1; Thu, 24 Sep 2020 11:00:25 -0400 X-MC-Unique: lTQRB-_VPU2rFBtOwp75YA-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 9A61C1017DD1; Thu, 24 Sep 2020 15:00:22 +0000 (UTC) Received: from file01.intranet.prod.int.rdu2.redhat.com (file01.intranet.prod.int.rdu2.redhat.com [10.11.5.7]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 37D877368C; Thu, 24 Sep 2020 15:00:22 +0000 (UTC) Received: from file01.intranet.prod.int.rdu2.redhat.com (localhost [127.0.0.1]) by file01.intranet.prod.int.rdu2.redhat.com (8.14.4/8.14.4) with ESMTP id 08OF0LbJ018758; Thu, 24 Sep 2020 11:00:21 -0400 Received: from localhost (mpatocka@localhost) by file01.intranet.prod.int.rdu2.redhat.com (8.14.4/8.14.4/Submit) with ESMTP id 08OF0KDN018754; Thu, 24 Sep 2020 11:00:21 -0400 X-Authentication-Warning: file01.intranet.prod.int.rdu2.redhat.com: mpatocka owned process doing -bs Date: Thu, 24 Sep 2020 11:00:20 -0400 (EDT) From: Mikulas Patocka X-X-Sender: mpatocka@file01.intranet.prod.int.rdu2.redhat.com To: Matthew Wilcox cc: Dave Chinner , Dan Williams , Linus Torvalds , Alexander Viro , Andrew Morton , Vishal Verma , Dave Jiang , Ira Weiny , Jan Kara , Eric Sandeen , Dave Chinner , "Kani, Toshi" , "Norton, Scott J" , "Tadakamadla, Rajesh (DCIG/CDI/HPS Perf)" , Linux Kernel Mailing List , linux-fsdevel , linux-nvdimm Subject: Re: NVFS XFS metadata (was: [PATCH] pmem: export the symbols __copy_user_flushcache and __copy_from_user_flushcache) In-Reply-To: <20200922172553.GL32101@casper.infradead.org> Message-ID: References:

<20200922050314.GB12096@dread.disaster.area> <20200922172553.GL32101@casper.infradead.org> User-Agent: Alpine 2.02 (LRH 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 22 Sep 2020, Matthew Wilcox wrote: > > > The NVFS indirect block tree has a fan-out of 16, > > > > No. The top level in the inode contains 16 blocks (11 direct and 5 > > indirect). And each indirect block can have 512 pointers (4096/8). You can > > format the device with larger block size and this increases the fanout > > (the NVFS block size must be greater or equal than the system page size). > > > > 2 levels can map 1GiB (4096*512^2), 3 levels can map 512 GiB, 4 levels can > > map 256 TiB and 5 levels can map 128 PiB. > > But compare to an unfragmented file ... you can map the entire thing with > a single entry. Even if you have to use a leaf node, you can get four > extents in a single cacheline (and that's a fairly naive leaf node layout; > I don't know exactly what XFS uses) But the benchmarks show that it is comparable to extent-based filesystems. > > > Rename is another operation that has specific "operation has atomic > > > behaviour" expectations. I haven't looked at how you've > > > implementated that yet, but I suspect it also is extremely difficult > > > to implement in an atomic manner using direct pmem updates to the > > > directory structures. > > > > There is a small window when renamed inode is neither in source nor in > > target directory. Fsck will reclaim such inode and add it to lost+found - > > just like on EXT2. > > ... ouch. If you have to choose, it'd be better to link it to the second > directory then unlink it from the first one. Then your fsck can detect > it has the wrong count and fix up the count (ie link it into both > directories rather than neither). I admit that this is lame and I'll fix it. Rename is not so performance-critical, so I can add a small journal for this. > > If you think that the lack of journaling is show-stopper, I can implement > > it. But then, I'll have something that has complexity of EXT4 and > > performance of EXT4. So that there will no longer be any reason why to use > > NVFS over EXT4. Without journaling, it will be faster than EXT4 and it may > > attract some users who want good performance and who don't care about GID > > and UID being updated atomically, etc. > > Well, what's your intent with nvfs? Do you already have customers in mind > who want to use this in production, or is this somewhere to play with and > develop concepts that might make it into one of the longer-established > filesystems? I develop it just because I thought it may be interesting. So far, it doesn't have any serious users (the physical format is still changing). I hope that it could be useable as a general purpose root filesystem when Optane DIMMs become common. Mikulas