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Fri, 21 Aug 2020 06:06:47 -0400 X-MC-Unique: jE53C10DM5GX5Q25Zgz-DA-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 C39C21005E74; Fri, 21 Aug 2020 10:06:44 +0000 (UTC) Received: from [10.36.114.87] (ovpn-114-87.ams2.redhat.com [10.36.114.87]) by smtp.corp.redhat.com (Postfix) with ESMTP id D831F7AEC2; Fri, 21 Aug 2020 10:06:41 +0000 (UTC) Subject: Re: [PATCH v4 11/23] device-dax: Kill dax_kmem_res To: Dan Williams , akpm@linux-foundation.org Cc: Vishal Verma , Dave Hansen , Pavel Tatashin , peterz@infradead.org, ard.biesheuvel@linaro.org, linux-mm@kvack.org, linux-nvdimm@lists.01.org, joao.m.martins@oracle.com, linux-kernel@vger.kernel.org, linux-acpi@vger.kernel.org, dri-devel@lists.freedesktop.org References: <159643094279.4062302.17779410714418721328.stgit@dwillia2-desk3.amr.corp.intel.com> <159643100485.4062302.976628339798536960.stgit@dwillia2-desk3.amr.corp.intel.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <159643100485.4062302.976628339798536960.stgit@dwillia2-desk3.amr.corp.intel.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Rspamd-Queue-Id: 6E12B180AD81A X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam03 Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 03.08.20 07:03, Dan Williams wrote: > Several related issues around this unneeded attribute: >=20 > - The dax_kmem_res property allows the kmem driver to stash the adjuste= d > resource range that was used for the hotplug operation, but that can = be > recalculated from the original base range. >=20 > - kmem is using an open coded release_resource() + kfree() when an > idiomatic release_mem_region() is sufficient. >=20 > - The driver managed resource need only manage the busy flag. Other fla= gs > are of no concern to the kmem driver. In fact if kmem inherits some > memory range that add_memory_driver_managed() rejects that is a > memory-hotplug-core policy that the driver is in no position to > override. >=20 > - The implementation trusts that failed remove_memory() results in the > entire resource range remaining pinned busy. The driver need not make > that layering violation assumption and just maintain the busy state i= n > its local resource. >=20 > - The "Hot-remove not yet implemented." comment is stale since hotremov= e > support is now included. I think some of these changes could have been nicely split out to simplify reviewing. E.g., comment update, release_mem_region(), &=3D ~IORESOURCE_BUSY ... [...] > + > int dev_dax_kmem_probe(struct device *dev) > { > struct dev_dax *dev_dax =3D to_dev_dax(dev); > - struct range *range =3D &dev_dax->range; > - resource_size_t kmem_start; > - resource_size_t kmem_size; > - resource_size_t kmem_end; > - struct resource *new_res; > - const char *new_res_name; > - int numa_node; > + struct range range =3D dax_kmem_range(dev_dax); > + int numa_node =3D dev_dax->target_node; > + struct resource *res; > + char *res_name; > int rc; > =20 > /* > @@ -37,109 +45,94 @@ int dev_dax_kmem_probe(struct device *dev) > * could be mixed in a node with faster memory, causing > * unavoidable performance issues. > */ > - numa_node =3D dev_dax->target_node; > if (numa_node < 0) { > dev_warn(dev, "rejecting DAX region with invalid node: %d\n", > numa_node); > return -EINVAL; > } > =20 > - /* Hotplug starting at the beginning of the next block: */ > - kmem_start =3D ALIGN(range->start, memory_block_size_bytes()); > - > - kmem_size =3D range_len(range); > - /* Adjust the size down to compensate for moving up kmem_start: */ > - kmem_size -=3D kmem_start - range->start; > - /* Align the size down to cover only complete blocks: */ > - kmem_size &=3D ~(memory_block_size_bytes() - 1); > - kmem_end =3D kmem_start + kmem_size; > - > - new_res_name =3D kstrdup(dev_name(dev), GFP_KERNEL); > - if (!new_res_name) > + res_name =3D kstrdup(dev_name(dev), GFP_KERNEL); > + if (!res_name) > return -ENOMEM; > =20 > - /* Region is permanently reserved if hotremove fails. */ > - new_res =3D request_mem_region(kmem_start, kmem_size, new_res_name); > - if (!new_res) { > - dev_warn(dev, "could not reserve region [%pa-%pa]\n", > - &kmem_start, &kmem_end); > - kfree(new_res_name); > + res =3D request_mem_region(range.start, range_len(&range), res_name); I think our range could be empty after aligning. I assume request_mem_region() would check that, but maybe we could report a better error/warning in that case. > + if (!res) { > + dev_warn(dev, "could not reserve region [%#llx-%#llx]\n", > + range.start, range.end); > + kfree(res_name); > return -EBUSY; > } > =20 > /* > - * Set flags appropriate for System RAM. Leave ..._BUSY clear > - * so that add_memory() can add a child resource. Do not > - * inherit flags from the parent since it may set new flags > - * unknown to us that will break add_memory() below. > + * Temporarily clear busy to allow add_memory_driver_managed() > + * to claim it. > */ > - new_res->flags =3D IORESOURCE_SYSTEM_RAM; > + res->flags &=3D ~IORESOURCE_BUSY; Right, same approach is taken by virtio-mem. > =20 > /* > * Ensure that future kexec'd kernels will not treat this as RAM > * automatically. > */ > - rc =3D add_memory_driver_managed(numa_node, new_res->start, > - resource_size(new_res), kmem_name); > + rc =3D add_memory_driver_managed(numa_node, res->start, > + resource_size(res), kmem_name); > + > + res->flags |=3D IORESOURCE_BUSY; Hm, I don't think that's correct. Any specific reason why to mark the not-added, unaligned parts BUSY? E.g., walk_system_ram_range() could suddenly stumble over it - and e.g., similarly kexec code when trying to find memory for placing kexec images. I think we should leave this !BUSY, just as it is right now. > if (rc) { > - release_resource(new_res); > - kfree(new_res); > - kfree(new_res_name); > + release_mem_region(range.start, range_len(&range)); > + kfree(res_name); > return rc; > } > - dev_dax->dax_kmem_res =3D new_res; > + > + dev_set_drvdata(dev, res_name); > =20 > return 0; > } > =20 > #ifdef CONFIG_MEMORY_HOTREMOVE > -static int dev_dax_kmem_remove(struct device *dev) > +static void dax_kmem_release(struct dev_dax *dev_dax) > { > - struct dev_dax *dev_dax =3D to_dev_dax(dev); > - struct resource *res =3D dev_dax->dax_kmem_res; > - resource_size_t kmem_start =3D res->start; > - resource_size_t kmem_size =3D resource_size(res); > - const char *res_name =3D res->name; > int rc; > + struct device *dev =3D &dev_dax->dev; > + const char *res_name =3D dev_get_drvdata(dev); > + struct range range =3D dax_kmem_range(dev_dax); > =20 > /* > * We have one shot for removing memory, if some memory blocks were n= ot > * offline prior to calling this function remove_memory() will fail, = and > * there is no way to hotremove this memory until reboot because devi= ce > - * unbind will succeed even if we return failure. > + * unbind will proceed regardless of the remove_memory result. > */ > - rc =3D remove_memory(dev_dax->target_node, kmem_start, kmem_size); > - if (rc) { > - any_hotremove_failed =3D true; > - dev_err(dev, > - "DAX region %pR cannot be hotremoved until the next reboot\n", > - res); > - return rc; > + rc =3D remove_memory(dev_dax->target_node, range.start, range_len(&ra= nge)); > + if (rc =3D=3D 0) { if (!rc) ? > + release_mem_region(range.start, range_len(&range)); remove_memory() does a release_mem_region_adjustable(). Don't you actually want to release the *unaligned* region you requested? > + dev_set_drvdata(dev, NULL); > + kfree(res_name); > + return; > } Not sure if inverting the error handling improved the code / review here. > =20 > - /* Release and free dax resources */ > - release_resource(res); > - kfree(res); > - kfree(res_name); > - dev_dax->dax_kmem_res =3D NULL; > - > - return 0; > + any_hotremove_failed =3D true; > + dev_err(dev, "%#llx-%#llx cannot be hotremoved until the next reboot\= n", > + range.start, range.end); > } > #else > -static int dev_dax_kmem_remove(struct device *dev) > +static void dax_kmem_release(struct dev_dax *dev_dax) > { > /* > - * Without hotremove purposely leak the request_mem_region() for the > - * device-dax range and return '0' to ->remove() attempts. The remova= l > - * of the device from the driver always succeeds, but the region is > - * permanently pinned as reserved by the unreleased > - * request_mem_region(). > + * Without hotremove purposely leak the request_mem_region() for > + * the device-dax range attempts. The removal of the device from > + * the driver always succeeds, but the region is permanently > + * pinned as reserved by the unreleased request_mem_region(). > */ > any_hotremove_failed =3D true; > - return 0; > } > #endif /* CONFIG_MEMORY_HOTREMOVE */ > =20 > +static int dev_dax_kmem_remove(struct device *dev) > +{ > + dax_kmem_release(to_dev_dax(dev)); > + return 0; > +} > + > static struct dax_device_driver device_dax_kmem_driver =3D { > .drv =3D { > .probe =3D dev_dax_kmem_probe, >=20 Maybe split some of these changes out. Would at least help me to review ;= ) --=20 Thanks, David / dhildenb