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From: Vishal Verma <vishal.l.verma@intel.com>
To: <linux-nvdimm@lists.01.org>
Cc: Dave Hansen <dave.hansen@linux.intel.com>,
	Ben Olson <ben.olson@intel.com>,
	Michal Biesek <michal.biesek@intel.com>
Subject: [ndctl PATCH 08/10] Documentation: clarify memory movablity for reconfigure-device
Date: Wed,  2 Oct 2019 17:49:23 -0600
Message-ID: <20191002234925.9190-9-vishal.l.verma@intel.com> (raw)
In-Reply-To: <20191002234925.9190-1-vishal.l.verma@intel.com>

Move the note about potential races in memory onlining into the
'Description' section to make it more prominent. Reword the note to talk
about the sources of such races, and talk about the new 'race detection'
semantics in daxctl.

Link: https://github.com/pmem/ndctl/issues/110
Reported-by: Ben Olson <ben.olson@intel.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>
---
 .../daxctl/daxctl-reconfigure-device.txt      | 24 +++++++++++--------
 1 file changed, 14 insertions(+), 10 deletions(-)

diff --git a/Documentation/daxctl/daxctl-reconfigure-device.txt b/Documentation/daxctl/daxctl-reconfigure-device.txt
index 196d692..4663529 100644
--- a/Documentation/daxctl/daxctl-reconfigure-device.txt
+++ b/Documentation/daxctl/daxctl-reconfigure-device.txt
@@ -97,6 +97,20 @@ error reconfiguring devices: Operation not supported
 reconfigured 0 devices
 ----
 
+'daxctl-reconfigure-device' nominally expects that it will online new memory
+blocks as 'movable', so that kernel data doesn't make it into this memory.
+However, there are other potential agents that may be configured to
+automatically online new hot-plugged memory as it appears. Most notably,
+these are the '/sys/devices/system/memory/auto_online_blocks' configuration,
+or system udev rules. If such an agent races to online memory sections, daxctl
+checks if the blocks were onlined as 'movable' memory. If this was not the
+case, and the memory blocks are found to be in a different zone, then a
+warning is displayed. If it is desired that a different agent control the
+onlining of memory blocks, and the associated memory zone, then it is
+recommended to use the --no-online option described below. This will abridge
+the device reconfiguration operation to just hotplugging the memory, and
+refrain from then onlining it.
+
 OPTIONS
 -------
 -r::
@@ -121,16 +135,6 @@ OPTIONS
 	brought online automatically and immediately with the 'online_movable'
 	policy. Use this option to disable the automatic onlining behavior.
 
-	NOTE: While this option prevents daxctl from automatically onlining
-	the memory sections, there may be other agents, notably system udev
-	rules, that online new memory sections as they appear. Coordinating
-	with such rules is out of scope of this utility, and the system
-	administrator is expected to remove them if they are undesirable.
-	If such an agent races to online memory sections, daxctl is prepared
-	to lose the race, and not fail the onlining operation as it only
-	cares that the memory section was onlined, not that it was the one
-	to do so.
-
 -f::
 --force::
 	When converting from "system-ram" mode to "devdax", it is expected
-- 
2.20.1
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  parent reply index

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-02 23:49 [ndctl PATCH 00/10] fixes and movability for system-ram mode Vishal Verma
2019-10-02 23:49 ` [ndctl PATCH 01/10] libdaxctl: refactor path construction in op_for_one_memblock() Vishal Verma
2019-10-18 18:43   ` Dan Williams
2019-10-02 23:49 ` [ndctl PATCH 02/10] libdaxctl: refactor memblock_is_online() checks Vishal Verma
2019-10-18 18:45   ` Dan Williams
2019-10-02 23:49 ` [ndctl PATCH 03/10] daxctl/device.c: fix json output omission for reconfigure-device Vishal Verma
2019-10-18 18:46   ` Dan Williams
2019-10-02 23:49 ` [ndctl PATCH 04/10] libdaxctl: add an API to determine if memory is movable Vishal Verma
2019-10-18 18:54   ` Dan Williams
2019-10-18 19:57     ` Verma, Vishal L
2019-10-18 20:40       ` Dan Williams
2019-10-02 23:49 ` [ndctl PATCH 05/10] libdaxctl: allow memblock_in_dev() to return an error Vishal Verma
2019-10-18 19:15   ` Dan Williams
2019-10-02 23:49 ` [ndctl PATCH 06/10] daxctl: show a 'movable' attribute in device listings Vishal Verma
2019-10-18 19:16   ` Dan Williams
2019-10-02 23:49 ` [ndctl PATCH 07/10] daxctl: detect races when onlining memory blocks Vishal Verma
2019-10-18 19:26   ` Dan Williams
2019-10-02 23:49 ` Vishal Verma [this message]
2019-10-18 20:46   ` [ndctl PATCH 08/10] Documentation: clarify memory movablity for reconfigure-device Dan Williams
2019-10-18 20:50     ` Verma, Vishal L
2019-10-02 23:49 ` [ndctl PATCH 09/10] libdaxctl: add an API to online memory in a non-movable state Vishal Verma
2019-10-18 20:54   ` Dan Williams
2019-10-02 23:49 ` [ndctl PATCH 10/10] daxctl: add --no-movable option for onlining memory Vishal Verma
2019-10-18 20:58   ` Dan Williams
2019-10-18 21:04     ` Verma, Vishal L
2019-10-18 21:25       ` Dan Williams

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