Re: [PATCH 5/5] ACPI / memhotplug: Drop unnecessary code

["Rafael J. Wysocki" <rjw@sisk.pl>]

On Monday, May 20, 2013 11:27:56 AM Toshi Kani wrote:
> On Sun, 2013-05-19 at 01:34 +0200, Rafael J. Wysocki wrote:
> > From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> > 
> > Now that the memory offlining should be taken care of by the
> > companion device offlining code in acpi_scan_hot_remove(), the
> > ACPI memory hotplug driver doesn't need to offline it in
> > acpi_memory_remove_memory() any more.  Consequently, it doesn't
> > need to call remove_memory() any more, which means that that
> > funtion may be dropped entirely, because acpi_memory_remove_memory()
> > is the only user of it.
> 
> The off-lining part of remove_memory() can be removed, but not the
> hot-delete part.  Please see my comments below.
> 
> > Make the changes described above to get rid of the dead code.
> > 
> > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> > ---
> >  drivers/acpi/acpi_memhotplug.c |   15 ------
> >  include/linux/memory_hotplug.h |    1 
> >  mm/memory_hotplug.c            |  102 -----------------------------------------
> >  3 files changed, 2 insertions(+), 116 deletions(-)
> > 
> > Index: linux-pm/drivers/acpi/acpi_memhotplug.c
> > ===================================================================
> > --- linux-pm.orig/drivers/acpi/acpi_memhotplug.c
> > +++ linux-pm/drivers/acpi/acpi_memhotplug.c
> > @@ -271,31 +271,20 @@ static int acpi_memory_enable_device(str
> >  	return 0;
> >  }
> >  
> > -static int acpi_memory_remove_memory(struct acpi_memory_device *mem_device)
> > +static void acpi_memory_remove_memory(struct acpi_memory_device *mem_device)
> >  {
> >  	acpi_handle handle = mem_device->device->handle;
> > -	int result = 0, nid;
> >  	struct acpi_memory_info *info, *n;
> >  
> > -	nid = acpi_get_node(handle);
> > -
> >  	list_for_each_entry_safe(info, n, &mem_device->res_list, list) {
> >  		if (!info->enabled)
> >  			continue;
> >  
> > -		if (nid < 0)
> > -			nid = memory_add_physaddr_to_nid(info->start_addr);
> > -
> > +		/* All of the memory blocks are offline at this point. */
> >  		acpi_unbind_memory_blocks(info, handle);
> > -		result = remove_memory(nid, info->start_addr, info->length);
> 
> We still need to call remove_memory().
> 
> > -		if (result)
> > -			return result;
> > -
> >  		list_del(&info->list);
> >  		kfree(info);
> >  	}
> > -
> > -	return result;
> >  }
> >  
> >  static void acpi_memory_device_free(struct acpi_memory_device *mem_device)
> > Index: linux-pm/include/linux/memory_hotplug.h
> > ===================================================================
> > --- linux-pm.orig/include/linux/memory_hotplug.h
> > +++ linux-pm/include/linux/memory_hotplug.h
> > @@ -252,7 +252,6 @@ extern int add_memory(int nid, u64 start
> >  extern int arch_add_memory(int nid, u64 start, u64 size);
> >  extern int offline_pages(unsigned long start_pfn, unsigned long nr_pages);
> >  extern bool is_memblock_offlined(struct memory_block *mem);
> > -extern int remove_memory(int nid, u64 start, u64 size);
> >  extern int sparse_add_one_section(struct zone *zone, unsigned long start_pfn,
> >  								int nr_pages);
> >  extern void sparse_remove_one_section(struct zone *zone, struct mem_section *ms);
> > Index: linux-pm/mm/memory_hotplug.c
> > ===================================================================
> > --- linux-pm.orig/mm/memory_hotplug.c
> > +++ linux-pm/mm/memory_hotplug.c
> > @@ -1670,41 +1670,6 @@ int walk_memory_range(unsigned long star
> >  }
> 
>  :
> 
> > -
> > -int __ref remove_memory(int nid, u64 start, u64 size)
> > -{
> > -	unsigned long start_pfn, end_pfn;
> > -	int ret = 0;
> > -	int retry = 1;
> > -
> > -	start_pfn = PFN_DOWN(start);
> > -	end_pfn = PFN_UP(start + size - 1);
> > -
> > -	/*
> > -	 * When CONFIG_MEMCG is on, one memory block may be used by other
> > -	 * blocks to store page cgroup when onlining pages. But we don't know
> > -	 * in what order pages are onlined. So we iterate twice to offline
> > -	 * memory:
> > -	 * 1st iterate: offline every non primary memory block.
> > -	 * 2nd iterate: offline primary (i.e. first added) memory block.
> > -	 */
> > -repeat:
> > -	walk_memory_range(start_pfn, end_pfn, &ret,
> > -			  offline_memory_block_cb);
> > -	if (ret) {
> > -		if (!retry)
> > -			return ret;
> > -
> > -		retry = 0;
> > -		ret = 0;
> > -		goto repeat;
> > -	}
> 
> The above procedure can be removed as it is for off-lining.
> 
> > -	lock_memory_hotplug();
> > -
> > -	/*
> > -	 * we have offlined all memory blocks like this:
> > -	 *   1. lock memory hotplug
> > -	 *   2. offline a memory block
> > -	 *   3. unlock memory hotplug
> > -	 *
> > -	 * repeat step1-3 to offline the memory block. All memory blocks
> > -	 * must be offlined before removing memory. But we don't hold the
> > -	 * lock in the whole operation. So we should check whether all
> > -	 * memory blocks are offlined.
> > -	 */
> > -
> > -	ret = walk_memory_range(start_pfn, end_pfn, NULL,
> > -				is_memblock_offlined_cb);
> > -	if (ret) {
> > -		unlock_memory_hotplug();
> > -		return ret;
> > -	}
> > -
> 
> I think the above procedure is still useful for safe guard.

But then it shoud to BUG_ON() instead of returning an error (which isn't very
useful for anything now).

> > -	/* remove memmap entry */
> > -	firmware_map_remove(start, start + size, "System RAM");
> > -
> > -	arch_remove_memory(start, size);
> > -
> > -	try_offline_node(nid);
> 
> The above procedure performs memory hot-delete specific operations and
> is necessary.

OK, I see.  I'll replace this patch with something simpler, then.

What about the other patches in the series?

Thanks,
Rafael


-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.

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