linux-kernel - [PATCH] cxl,documentation: remove page-allocator quirk section

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [day] [month] [year] [list]

Message-ID: <20250817172002.43488-1-gourry@gourry.net>
Date: Sun, 17 Aug 2025 13:20:02 -0400
From: Gregory Price <gourry@...rry.net>
To: linux-cxl@...r.kernel.org
Cc: linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	dave@...olabs.net,
	jonathan.cameron@...wei.com,
	dave.jiang@...el.com,
	alison.schofield@...el.com,
	vishal.l.verma@...el.com,
	ira.weiny@...el.com,
	dan.j.williams@...el.com,
	corbet@....net,
	Gregory Price <gourry@...rry.net>
Subject: [PATCH] cxl,documentation: remove page-allocator quirk section

The node/zone quirk section of the cxl documentation is incorrect.
The actual reason for fallback allocation misbehavior in the
described configuration is due to how reclaim is engaged when
the local nodes capacity is exhausted when nodes have no overlapping
zones.  No fix is available for this issue yet, but the documentation
here is incorrect, so simply remove it.

Signed-off-by: Gregory Price <gourry@...rry.net>
---
 .../cxl/allocation/page-allocator.rst         | 31 -------------------
 1 file changed, 31 deletions(-)

diff --git a/Documentation/driver-api/cxl/allocation/page-allocator.rst b/Documentation/driver-api/cxl/allocation/page-allocator.rst
index 7b8fe1b8d5bb..3fa584a248bd 100644
--- a/Documentation/driver-api/cxl/allocation/page-allocator.rst
+++ b/Documentation/driver-api/cxl/allocation/page-allocator.rst
@@ -41,37 +41,6 @@ To simplify this, the page allocator will prefer :code:`ZONE_MOVABLE` over
 will fallback to allocate from :code:`ZONE_NORMAL`.
 
 
-Zone and Node Quirks
-====================
-Let's consider a configuration where the local DRAM capacity is largely onlined
-into :code:`ZONE_NORMAL`, with no :code:`ZONE_MOVABLE` capacity present. The
-CXL capacity has the opposite configuration - all onlined in
-:code:`ZONE_MOVABLE`.
-
-Under the default allocation policy, the page allocator will completely skip
-:code:`ZONE_MOVABLE` as a valid allocation target.  This is because, as of
-Linux v6.15, the page allocator does (approximately) the following: ::
-
-  for (each zone in local_node):
-
-    for (each node in fallback_order):
-
-      attempt_allocation(gfp_flags);
-
-Because the local node does not have :code:`ZONE_MOVABLE`, the CXL node is
-functionally unreachable for direct allocation.  As a result, the only way
-for CXL capacity to be used is via `demotion` in the reclaim path.
-
-This configuration also means that if the DRAM ndoe has :code:`ZONE_MOVABLE`
-capacity - when that capacity is depleted, the page allocator will actually
-prefer CXL :code:`ZONE_MOVABLE` pages over DRAM :code:`ZONE_NORMAL` pages.
-
-We may wish to invert this priority in future Linux versions.
-
-If `demotion` and `swap` are disabled, Linux will begin to cause OOM crashes
-when the DRAM nodes are depleted. See the reclaim section for more details.
-
-
 CGroups and CPUSets
 ===================
 Finally, assuming CXL memory is reachable via the page allocation (i.e. onlined
-- 
2.50.1