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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2C07DC433F5 for ; Fri, 22 Oct 2021 01:58:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0A7406103E for ; Fri, 22 Oct 2021 01:58:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231857AbhJVCAg (ORCPT ); Thu, 21 Oct 2021 22:00:36 -0400 Received: from mail.kernel.org ([198.145.29.99]:51914 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230190AbhJVCAe (ORCPT ); Thu, 21 Oct 2021 22:00:34 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id ED74B610A4; Fri, 22 Oct 2021 01:58:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1634867898; bh=c8L9yqtOQno8QSB3ULMQffUkwUDJVg6kdYBJfcJdcMA=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=g96XX9a9mSzi+2Kx8RQ65PHbUXgZ2eHNAQIWuMSIRrTBzOUvQPgi5vg7LPK9jBGam lhTH6OnHe8C4q0Z0fffRat2tjJm11r4Xl3d1NN3AtZ/bcJsob4EBmVShieUBmddcQC JnE8VxHAUpAJ2fpmr//vA/LJG/GzeUD+AyrZnVWFMo1H4oneozj04Es+3/SQuZ0S6a TYQiwROwM/MjigR9TyUx0DfDMbS1p67KpKym7AGZUF/QgzOdMtAyXjl99x9/YoDQuo Y7iuj0g//1S/3IbkzGZ2auNMbJoHshMwMUyWtSyav15RFt3KksZ4m+wBYIA/tMw03e UIYh/NQ7wXFUg== Date: Thu, 21 Oct 2021 18:58:17 -0700 From: "Darrick J. Wong" To: Jane Chu Cc: Christoph Hellwig , "david@fromorbit.com" , "dan.j.williams@intel.com" , "vishal.l.verma@intel.com" , "dave.jiang@intel.com" , "agk@redhat.com" , "snitzer@redhat.com" , "dm-devel@redhat.com" , "ira.weiny@intel.com" , "willy@infradead.org" , "vgoyal@redhat.com" , "linux-fsdevel@vger.kernel.org" , "nvdimm@lists.linux.dev" , "linux-kernel@vger.kernel.org" , "linux-xfs@vger.kernel.org" Subject: Re: [dm-devel] [PATCH 0/6] dax poison recovery with RWF_RECOVERY_DATA flag Message-ID: <20211022015817.GY24307@magnolia> References: <20211021001059.438843-1-jane.chu@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Oct 22, 2021 at 01:37:28AM +0000, Jane Chu wrote: > On 10/21/2021 4:31 AM, Christoph Hellwig wrote: > > Looking over the series I have serious doubts that overloading the > > slow path clear poison operation over the fast path read/write > > path is such a great idea. Why would data recovery after a media error ever be considered a fast/hot path? A normal read/write to a fsdax file would not pass the flag, which skips the poison checking with whatever MCE consequences that has, right? pwritev2(..., RWF_RECOVER_DATA) should be infrequent enough that carefully stepping around dax_direct_access only has to be faster than restoring from backup, I hope? > Understood, sounds like a concern on principle. But it seems to me > that the task of recovery overlaps with the normal write operation > on the write part. Without overloading some write operation for > 'recovery', I guess we'll need to come up with a new userland > command coupled with a new dax API ->clear_poison and propagate the > new API support to each dm targets that support dax which, again, > is an idea that sounds too bulky if I recall Dan's earlier rejection > correctly. > > It is in my plan though, to provide pwritev2(2) and preadv2(2) man pages > with description about the RWF_RECOVERY_DATA flag and specifically not > recommending the flag for normal read/write operation - due to potential > performance impact from searching badblocks in the range. Yes, this will help much. :) > That said, the badblock searching is turned on only if the pmem device > contains badblocks(i.e. bb->count > 0), otherwise, the performance > impact is next to none. And once the badblock search starts, > it is a binary search over user provided range. The unwanted impact > happens to be the case when the pmem device contains badblocks > that do not fall in the user specified range, and in that case, the > search would end in O(1). (I wonder about improving badblocks to be less sector-oriented and not have that weird 16-records-max limit, but that can be a later optimization.) --D > Thanks! > -jane > >