linux-kernel - Re: [PATCH v2 4/8] mm/memory_hotplug: Create memory block devices after arch_add

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Message-ID: <20190509143151.zexjmwu3ikkmye7i@master>
Date:   Thu, 9 May 2019 14:31:51 +0000
From:   Wei Yang <richard.weiyang@...il.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        linux-ia64@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-s390@...r.kernel.org, linux-sh@...r.kernel.org,
        akpm@...ux-foundation.org, Dan Williams <dan.j.williams@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        "mike.travis@....com" <mike.travis@....com>,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Banman <andrew.banman@....com>,
        Oscar Salvador <osalvador@...e.de>,
        Michal Hocko <mhocko@...e.com>,
        Pavel Tatashin <pasha.tatashin@...een.com>,
        Qian Cai <cai@....pw>, Wei Yang <richard.weiyang@...il.com>,
        Arun KS <arunks@...eaurora.org>,
        Mathieu Malaterre <malat@...ian.org>
Subject: Re: [PATCH v2 4/8] mm/memory_hotplug: Create memory block devices
 after arch_add_memory()

On Tue, May 07, 2019 at 08:38:00PM +0200, David Hildenbrand wrote:
>Only memory to be added to the buddy and to be onlined/offlined by
>user space using memory block devices needs (and should have!) memory
>block devices.
>
>Factor out creation of memory block devices Create all devices after
>arch_add_memory() succeeded. We can later drop the want_memblock parameter,
>because it is now effectively stale.
>
>Only after memory block devices have been added, memory can be onlined
>by user space. This implies, that memory is not visible to user space at
>all before arch_add_memory() succeeded.
>
>Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
>Cc: "Rafael J. Wysocki" <rafael@...nel.org>
>Cc: David Hildenbrand <david@...hat.com>
>Cc: "mike.travis@....com" <mike.travis@....com>
>Cc: Andrew Morton <akpm@...ux-foundation.org>
>Cc: Ingo Molnar <mingo@...nel.org>
>Cc: Andrew Banman <andrew.banman@....com>
>Cc: Oscar Salvador <osalvador@...e.de>
>Cc: Michal Hocko <mhocko@...e.com>
>Cc: Pavel Tatashin <pasha.tatashin@...een.com>
>Cc: Qian Cai <cai@....pw>
>Cc: Wei Yang <richard.weiyang@...il.com>
>Cc: Arun KS <arunks@...eaurora.org>
>Cc: Mathieu Malaterre <malat@...ian.org>
>Signed-off-by: David Hildenbrand <david@...hat.com>
>---
> drivers/base/memory.c  | 70 ++++++++++++++++++++++++++----------------
> include/linux/memory.h |  2 +-
> mm/memory_hotplug.c    | 15 ++++-----
> 3 files changed, 53 insertions(+), 34 deletions(-)
>
>diff --git a/drivers/base/memory.c b/drivers/base/memory.c
>index 6e0cb4fda179..862c202a18ca 100644
>--- a/drivers/base/memory.c
>+++ b/drivers/base/memory.c
>@@ -701,44 +701,62 @@ static int add_memory_block(int base_section_nr)
> 	return 0;
> }
> 
>+static void unregister_memory(struct memory_block *memory)
>+{
>+	BUG_ON(memory->dev.bus != &memory_subsys);
>+
>+	/* drop the ref. we got via find_memory_block() */
>+	put_device(&memory->dev);
>+	device_unregister(&memory->dev);
>+}
>+
> /*
>- * need an interface for the VM to add new memory regions,
>- * but without onlining it.
>+ * Create memory block devices for the given memory area. Start and size
>+ * have to be aligned to memory block granularity. Memory block devices
>+ * will be initialized as offline.
>  */
>-int hotplug_memory_register(int nid, struct mem_section *section)
>+int hotplug_memory_register(unsigned long start, unsigned long size)

One trivial suggestion about the function name.

For memory_block device, sometimes we use the full name

    find_memory_block
    init_memory_block
    add_memory_block

But sometimes we use *nick* name

    hotplug_memory_register
    register_memory
    unregister_memory

This is a little bit confusion.

Can we use one name convention here? 

[...]

> /*
>@@ -1106,6 +1100,13 @@ int __ref add_memory_resource(int nid, struct resource *res)
> 	if (ret < 0)
> 		goto error;
> 
>+	/* create memory block devices after memory was added */
>+	ret = hotplug_memory_register(start, size);
>+	if (ret) {
>+		arch_remove_memory(nid, start, size, NULL);

Functionally, it works I think.

But arch_remove_memory() would remove pages from zone. At this point, we just
allocate section/mmap for pages, the zones are empty and pages are not
connected to zone.

Function  zone = page_zone(page); always gets zone #0, since pages->flags is 0
at  this point. This is not exact.

Would we add some comment to mention this? Or we need to clean up
arch_remove_memory() to take out __remove_zone()?


>+		goto error;
>+	}
>+
> 	if (new_node) {
> 		/* If sysfs file of new node can't be created, cpu on the node
> 		 * can't be hot-added. There is no rollback way now.
>-- 
>2.20.1

-- 
Wei Yang
Help you, Help me