linux-kernel - Re: [PATCH] [REPOST #2] mm: show node to memory section relationship with symlinks in sysfs

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Date:	Thu, 13 Nov 2008 08:54:02 -0800
From:	Gary Hade <garyhade@...ibm.com>
To:	Badari Pulavarty <pbadari@...ibm.com>
Cc:	Gary Hade <garyhade@...ibm.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Yasunori Goto <y-goto@...fujitsu.com>,
	Mel Gorman <mel@....ul.ie>, Chris McDermott <lcm@...ibm.com>,
	Ingo Molnar <mingo@...e.hu>, Greg KH <greg@...ah.com>,
	Dave Hansen <dave@...ux.vnet.ibm.com>,
	Nish Aravamudan <nish.aravamudan@...il.com>
Subject: Re: [PATCH] [REPOST #2] mm: show node to memory section
	relationship with symlinks in sysfs

On Wed, Nov 12, 2008 at 02:16:15PM -0800, Badari Pulavarty wrote:
> On Mon, 2008-11-03 at 15:48 -0800, Gary Hade wrote:
> > Show node to memory section relationship with symlinks in sysfs
> > 
> > Add /sys/devices/system/node/nodeX/memoryY symlinks for all
> > the memory sections located on nodeX.  For example:
> > /sys/devices/system/node/node1/memory135 -> ../../memory/memory135
> > indicates that memory section 135 resides on node1.
> > 
> > Also revises documentation to cover this change as well as updating
> > Documentation/ABI/testing/sysfs-devices-memory to include descriptions
> > of memory hotremove files 'phys_device', 'phys_index', and 'state'
> > that were previously not described there.
> > 
> > In addition to it always being a good policy to provide users with
> > the maximum possible amount of physical location information for
> > resources that can be hot-added and/or hot-removed, the following
> > are some (but likely not all) of the user benefits provided by
> > this change.
> > Immediate:
> >   - Provides information needed to determine the specific node
> >     on which a defective DIMM is located.  This will reduce system
> >     downtime when the node or defective DIMM is swapped out.
> >   - Prevents unintended onlining of a memory section that was 
> >     previously offlined due to a defective DIMM.  This could happen
> >     during node hot-add when the user or node hot-add assist script
> >     onlines _all_ offlined sections due to user or script inability
> >     to identify the specific memory sections located on the hot-added
> >     node.  The consequences of reintroducing the defective memory
> >     could be ugly.
> >   - Provides information needed to vary the amount and distribution
> >     of memory on specific nodes for testing or debugging purposes.
> > Future:
> >   - Will provide information needed to identify the memory
> >     sections that need to be offlined prior to physical removal
> >     of a specific node.
> > 
> > Symlink creation during boot was tested on 2-node x86_64, 2-node
> > ppc64, and 2-node ia64 systems.  Symlink creation during physical
> > memory hot-add tested on a 2-node x86_64 system.
> > 
> > Supersedes the "mm: show memory section to node relationship in sysfs"
> > patch posted on 05 Sept 2008 which created node ID containing 'node'
> > files in /sys/devices/system/memory/memoryX instead of symlinks.
> > Changed from files to symlinks due to feedback that symlinks were
> > more consistent with the sysfs way.
> > 
> > Supersedes the "mm: show node to memory section relationship with
> > symlinks in sysfs" patch posted on 29 Sept 2008 to address a Yasunori
> > Goto reported problem where an incorrect symlink was created due to
> > a range of uninitialized pages at the beginning of a section.  This
> > problem which produced a symlink in /sys/devices/system/node/node0
> > that incorrectly referenced a mem section located on node1 is corrected
> > in this version.  This version also covers the case were a mem section
> > could span multiple nodes.
> > 
> > Supersedes the "mm: show node to memory section relationship with
> > symlinks in sysfs" patch posted on 09 Oct 2008 to add the Andrew
> > Morton requested usefulness information and update to apply cleanly
> > to 2.6.28-rc3 and 2.6-git.  Code is unchanged.
> > 
> > Signed-off-by: Gary Hade <garyhade@...ibm.com>
> > Signed-off-by: Badari Pulavarty <pbadari@...ibm.com>
> > 
> 
> Hi Gary,
> 
> While testing latest mmtom (which has this patch) ran into an issue
> with sysfs files. What I noticed was, with this patch "memoryXX"
> directories in /sys/devices/system/memory/ are not getting cleaned up.
> Backing out the patch seems to fix the problem. 
> 
> When I tried to remove 64 blocks of memory, empty  directories are
> stayed around. (look at memory151 - memory215). This is causing OOPS
> while trying to add memory block again. I think this could be because 
> of the symlink added from node directory.  Can you look ?

Badari, The call to unregister_mem_sect_under_nodes() in
remove_memory_block() preceding the removal of the files in
the memory section directory _should have_ removed all the
symlinks referencing the memory section directory.  Did you
happen to check to see if the symlinks to memory151-memory215
were still present?

Gary

-- 
Gary Hade
System x Enablement
IBM Linux Technology Center
503-578-4503  IBM T/L: 775-4503
garyhade@...ibm.com
http://www.ibm.com/linux/ltc

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