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=-7.0 required=3.0 tests=DKIMWL_WL_MED,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_PASS autolearn=unavailable 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 C2996C10F14 for ; Thu, 11 Apr 2019 16:09:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 809DD217F4 for ; Thu, 11 Apr 2019 16:09:26 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=intel-com.20150623.gappssmtp.com header.i=@intel-com.20150623.gappssmtp.com header.b="OExIW2rN" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726842AbfDKQJY (ORCPT ); Thu, 11 Apr 2019 12:09:24 -0400 Received: from mail-ot1-f66.google.com ([209.85.210.66]:44574 "EHLO mail-ot1-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726709AbfDKQJQ (ORCPT ); Thu, 11 Apr 2019 12:09:16 -0400 Received: by mail-ot1-f66.google.com with SMTP id d24so5690247otl.11 for ; Thu, 11 Apr 2019 09:09:15 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=intel-com.20150623.gappssmtp.com; s=20150623; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=6e0pYzlyJULDAsD9P9xF/AncqgDFrFc74lsbm2pp/Hs=; b=OExIW2rNOO/AH8PIKD7PW7F27aEB3OXEbjCq6Q6tNZhacP/yTFe/CceQjwK6DhN3wH oSYVIYB+W1CWVwUu39E04NAG7rs/ZW1gmqb4pY9Use2kIavWy+EhYD9dN5hnfiBUSXa7 j3w2WgxABB/9K4yxGHWnWJWZyy+R14QZMxpiaHZKWxzjUW5L8YPQy+TwoIA6GuQM7Hb/ kuBcj3LTC3SIBPEhfvER2+1uq20CVu/8H3CWzdcmbXQ/4j4zE6By8oEOImglUSPjMCEC oSiyhWkjCY5wdaVgflK3PeIX2XQ3v/2wgv8tCDV4u4PMImHPgHDdehpn60Hs6bvMuDdZ 3Pgg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=6e0pYzlyJULDAsD9P9xF/AncqgDFrFc74lsbm2pp/Hs=; b=MWYxPLs9pEWwBZ7iU64EvpAziN/Q3TOZxE4AiyuyE48A7np3F9syUWr+fna6FnSCe2 c+xRh7fmBehOHrtkuLliVYvreDvQCi1ycLgQkUEv3EtG7nbK9GfUqdcjpZSvS98wqUjl n3/+kEU5AVMwuNn1krU/i2Pqaf3mf73Hf+MdHbmJGUZwhrh7ofux+pn8Jku4kWKMDbIP ebdpsD8W3Wnc/0A+vB76MYI+SDexoos7dnizQU8UeZBUOr8ledIwyInWDihhyh16eJMj KRibhz90Qmcey+UFAoPA2e/cz1ZDrf+3/hAFY0R1ey3sbsox64ij5t/9QTpG0m+wpkRh fb1g== X-Gm-Message-State: APjAAAWRAEOMghBZWuLqqN6DRnlxauEa8gJGxULa6bOpbyhIEZAJbCdi kFbalzeLymwMe+93w909qJsfRdCG0k0rj6j8P4cNew== X-Google-Smtp-Source: APXvYqxPfOYC3NUb5uxj6NsGBnQ6+dcHno8VW5WX9/9Ht+h/wnavf1GeLxLM1YyYYr5MU1loEyoELAeRjex0dJAYDmc= X-Received: by 2002:a9d:5c86:: with SMTP id a6mr31770148oti.118.1554998955333; Thu, 11 Apr 2019 09:09:15 -0700 (PDT) MIME-Version: 1.0 References: <20190410040826.24371-1-pagupta@redhat.com> <20190410040826.24371-2-pagupta@redhat.com> <1463291806.21158433.1554998258746.JavaMail.zimbra@redhat.com> In-Reply-To: <1463291806.21158433.1554998258746.JavaMail.zimbra@redhat.com> From: Dan Williams Date: Thu, 11 Apr 2019 09:09:03 -0700 Message-ID: Subject: Re: [Qemu-devel] [PATCH v5 1/6] libnvdimm: nd_region flush callback support To: Pankaj Gupta Cc: cohuck@redhat.com, Jan Kara , KVM list , "Michael S. Tsirkin" , Jason Wang , david , Qemu Developers , virtualization@lists.linux-foundation.org, Andreas Dilger , Ross Zwisler , Andrea Arcangeli , Dave Jiang , linux-nvdimm , Vishal L Verma , David Hildenbrand , Matthew Wilcox , Christoph Hellwig , Linux ACPI , jmoyer , linux-ext4 , Len Brown , kilobyte@angband.pl, Rik van Riel , yuval shaia , Stefan Hajnoczi , Paolo Bonzini , lcapitulino@redhat.com, Kevin Wolf , Nitesh Narayan Lal , "Theodore Ts'o" , Xiao Guangrong , "Darrick J. Wong" , "Rafael J. Wysocki" , Linux Kernel Mailing List , linux-xfs , linux-fsdevel , Igor Mammedov Content-Type: text/plain; charset="UTF-8" Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Thu, Apr 11, 2019 at 9:02 AM Pankaj Gupta wrote: > > > > > > > > > This patch adds functionality to perform flush from guest > > > to host over VIRTIO. We are registering a callback based > > > on 'nd_region' type. virtio_pmem driver requires this special > > > flush function. For rest of the region types we are registering > > > existing flush function. Report error returned by host fsync > > > failure to userspace. > > > > > > This also handles asynchronous flush requests from the block layer > > > by creating a child bio and chaining it with parent bio. > > > > > > Signed-off-by: Pankaj Gupta > > > ---bio_chain Dan williams > > [..] > > > diff --git a/drivers/nvdimm/region_devs.c b/drivers/nvdimm/region_devs.c > > > index b4ef7d9ff22e..fb1041ab32a6 100644 > > > --- a/drivers/nvdimm/region_devs.c > > > +++ b/drivers/nvdimm/region_devs.c > > > @@ -295,7 +295,9 @@ static ssize_t deep_flush_store(struct device *dev, > > > struct device_attribute *att > > > return rc; > > > if (!flush) > > > return -EINVAL; > > > - nvdimm_flush(nd_region); > > > + rc = nvdimm_flush(nd_region, NULL, false); > > > + if (rc) > > > + return rc; > > > > > > return len; > > > } > > > @@ -1085,6 +1087,11 @@ static struct nd_region *nd_region_create(struct > > > nvdimm_bus *nvdimm_bus, > > > dev->of_node = ndr_desc->of_node; > > > nd_region->ndr_size = resource_size(ndr_desc->res); > > > nd_region->ndr_start = ndr_desc->res->start; > > > + if (ndr_desc->flush) > > > + nd_region->flush = ndr_desc->flush; > > > + else > > > + nd_region->flush = generic_nvdimm_flush; > > > + > > > nd_device_register(dev); > > > > > > return nd_region; > > > @@ -1125,11 +1132,36 @@ struct nd_region > > > *nvdimm_volatile_region_create(struct nvdimm_bus *nvdimm_bus, > > > } > > > EXPORT_SYMBOL_GPL(nvdimm_volatile_region_create); > > > > > > +int nvdimm_flush(struct nd_region *nd_region, struct bio *bio, bool async) > > > +{ > > > > I don't quite see the point of the 'async' argument. All the usages of > > this routine are either > > > > nvdimm_flush(nd_region, bio, true) > > ...or: > > nvdimm_flush(nd_region, NULL, false) > > Agree. > > > > > ...so why not gate async behavior on the presence of the 'bio' argument? > > Sure. > > > > > > > > + int rc = 0; > > > + > > > + /* Create child bio for asynchronous flush and chain with > > > + * parent bio. Otherwise directly call nd_region flush. > > > + */ > > > + if (async && bio->bi_iter.bi_sector != -1) { > > > + > > > + struct bio *child = bio_alloc(GFP_ATOMIC, 0); > > > + > > > + if (!child) > > > + return -ENOMEM; > > > + bio_copy_dev(child, bio); > > > + child->bi_opf = REQ_PREFLUSH; > > > + child->bi_iter.bi_sector = -1; > > > + bio_chain(child, bio); > > > + submit_bio(child); > > > > I understand how this works, but it's a bit too "magical" for my > > taste. I would prefer that all flush implementations take an optional > > 'bio' argument rather than rely on the make_request implementation to > > stash the bio away on a driver specific list. > > I did this to make use of "bio_chain" for chaining child bio for async flush > suggested [1]. Are you saying to remove this and just call "flush" based on > bio argument? Or I implemented the 'bio_chain' request entirely wrong? No, I think you implemented it correctly. I'm just asking for the chaining to be performed internal to the ->flush() callback rather than in the common nvdimm_flush() front-end.