From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qa0-f54.google.com (mail-qa0-f54.google.com [209.85.216.54]) by kanga.kvack.org (Postfix) with ESMTP id 4668F6B0038 for ; Tue, 30 Sep 2014 17:52:56 -0400 (EDT) Received: by mail-qa0-f54.google.com with SMTP id i13so300146qae.41 for ; Tue, 30 Sep 2014 14:52:56 -0700 (PDT) Received: from omr2.cc.vt.edu (omr2.cc.ipv6.vt.edu. [2001:468:c80:2105:0:24d:7091:8b9c]) by mx.google.com with ESMTPS id kb2si17061062qcb.48.2014.09.30.14.52.44 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 30 Sep 2014 14:52:52 -0700 (PDT) Subject: Re: [PATCH v11 00/21] Add support for NV-DIMMs to ext4 In-Reply-To: Your message of "Tue, 30 Sep 2014 15:25:17 -0600." From: Valdis.Kletnieks@vt.edu References: <1411677218-29146-1-git-send-email-matthew.r.wilcox@intel.com> <15705.1412070301@turing-police.cc.vt.edu> <20140930144854.GA5098@wil.cx> <123795.1412088827@turing-police.cc.vt.edu> <20140930160841.GB5098@wil.cx> <15704.1412109476@turing-police.cc.vt.edu> Mime-Version: 1.0 Content-Type: multipart/signed; boundary="==_Exmh_1412113956_2351P"; micalg=pgp-sha1; protocol="application/pgp-signature" Content-Transfer-Encoding: 7bit Date: Tue, 30 Sep 2014 17:52:36 -0400 Message-ID: <62749.1412113956@turing-police.cc.vt.edu> Sender: owner-linux-mm@kvack.org List-ID: To: Andreas Dilger Cc: Matthew Wilcox , Matthew Wilcox , linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org --==_Exmh_1412113956_2351P Content-Type: text/plain; charset=us-ascii On Tue, 30 Sep 2014 15:25:17 -0600, Andreas Dilger said: > I think you would be much better off having more aggressive "use once" > semantics in the page cache, so that page cache pages for streaming > writes are evicted more aggressively from cache rather than going down > the "automatic O_DIRECT" hole. Well, I'm open to convincing.. an inode bit that says "I/O for this file is always first out of the page cache" would probably fix most of the thrashing page cache problem (and avoid the "unexpected O_DIRECT kills the program" issue), at the cost of a little more CPU when we turn around and evict it from the page cache. As long as we're at it, if we go that route we probably *also* want a way for a program to specify it at open() time (for instance, for the use of backup programs) - that should minimize the infamous "everything runs like a pig after the backup finishes running because the *useful* pages are all cache-cold". (And yes, you really *do* want the ability in both places - one for a program to be able to say "do this for any file I touch", and another for the file to say "do this for any program that touches me"). Matthew - would that sort of approach make more sense to you? I admit I originally posted only because I'd just finished fighting with a similar issue, and code floated by that got filesystem pages into core without trashing the page cache. I'm not at all tied to the specific solution.. :) --==_Exmh_1412113956_2351P Content-Type: application/pgp-signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 Comment: Exmh version 2.5 07/13/2001 iQIVAwUBVCsmJAdmEQWDXROgAQLF4w//bC27sR3tYMAXUDIz7gtBvyZfAgV6MZE8 ISyDvTbznH26Whpz2lnZovOYcOQ492pq7/aWVwmpvoRdERD+pXygtKx2UcCH3Pra c9H/VVUHmEH0gRM99olZtyvIIdGG4nGW4fs9orw6DfnEnrurhybWlQGNgeCe8HgV ul+FQ+zOW+fP7rrQBCGn/y1mA5yYWbWy8ox+/kYnX6X0noMDpSYndV05nLp95MC2 ThalxXom8Nxzi5J/aDKFpT7ihHEiCr6xiGV+EsyNGhIjtjR/Y/VhzsJ32f8aBBdh PqopyQvhNlfqY3jOKSIjaWbhatubQzyL5xcLQXRptok6xW90XXT9tDRr4mDshzhO UCOg7DQ8ylI6AVE6fVHD6cqSXu+VONSJRu1fBRTnSKbebKEz1pApXONkrFNRphsl yvm0dsT7cEF8qV6XRtl498nnNjeZv010x6L0aiP6gH7Uhb0DqlTfE0t+e5zaBe1T cubwHzDmxj4DLb0Iq6/KftAHq6J1zQ0EflHJH1al7VrUSoA0Ad8q1mBD0dN1KiQg DP6GU3n4PUhXBAO3K0z0DJdxvh8P54O3XOK808onOIvWEDLxiqrxjmTPSsehAtM6 O1P4ip2Ko93dEr7iFEtAM4RKD7ZBQlz7DQj5r9Dl2XvfdwRYvKtEwf/VLWb2vCv0 +90jeX7+1eM= =sOpo -----END PGP SIGNATURE----- --==_Exmh_1412113956_2351P-- -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org