The patch titled
Subject: docs: mm: add enable_soft_offline sysctl
has been added to the -mm mm-unstable branch. Its filename is
docs-mm-add-enable_soft_offline-sysctl.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/docs-mm-add-enable_soft_offline-sysctl.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Jiaqi Yan <jiaqiyan@xxxxxxxxxx>
Subject: docs: mm: add enable_soft_offline sysctl
Date: Mon, 17 Jun 2024 17:05:45 +0000
Add the documentation for soft offline behaviors / costs, and what
the new enable_soft_offline sysctl is for.
Link: https://lkml.kernel.org/r/20240617170545.3820912-4-jiaqiyan@xxxxxxxxxx
Signed-off-by: Jiaqi Yan <jiaqiyan@xxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Frank van der Linden <fvdl@xxxxxxxxxx>
Cc: Jane Chu <jane.chu@xxxxxxxxxx>
Cc: Jonathan Corbet <corbet@xxxxxxx>
Cc: Lance Yang <ioworker0@xxxxxxxxx>
Cc: Miaohe Lin <linmiaohe@xxxxxxxxxx>
Cc: Muchun Song <muchun.song@xxxxxxxxx>
Cc: Naoya Horiguchi <nao.horiguchi@xxxxxxxxx>
Cc: Oscar Salvador <osalvador@xxxxxxx>
Cc: Shuah Khan <shuah@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
Documentation/admin-guide/sysctl/vm.rst | 33 ++++++++++++++++++++++
1 file changed, 33 insertions(+)
--- a/Documentation/admin-guide/sysctl/vm.rst~docs-mm-add-enable_soft_offline-sysctl
+++ a/Documentation/admin-guide/sysctl/vm.rst
@@ -36,6 +36,7 @@ Currently, these files are in /proc/sys/
- dirtytime_expire_seconds
- dirty_writeback_centisecs
- drop_caches
+- enable_soft_offline
- extfrag_threshold
- highmem_is_dirtyable
- hugetlb_shm_group
@@ -267,6 +268,38 @@ used::
These are informational only. They do not mean that anything is wrong
with your system. To disable them, echo 4 (bit 2) into drop_caches.
+enable_soft_offline
+===================
+Correctable memory errors are very common on servers. Soft-offline is kernel's
+solution for memory pages having (excessive) corrected memory errors.
+
+For different types of page, soft-offline has different behaviors / costs.
+- For a raw error page, soft-offline migrates the in-use page's content to
+ a new raw page.
+- For a page that is part of a transparent hugepage, soft-offline splits the
+ transparent hugepage into raw pages, then migrates only the raw error page.
+ As a result, user is transparently backed by 1 less hugepage, impacting
+ memory access performance.
+- For a page that is part of a HugeTLB hugepage, soft-offline first migrates
+ the entire HugeTLB hugepage, during which a free hugepage will be consumed
+ as migration target. Then the original hugepage is dissolved into raw
+ pages without compensation, reducing the capacity of the HugeTLB pool by 1.
+
+It is user's call to choose between reliability (staying away from fragile
+physical memory) vs performance / capacity implications in transparent and
+HugeTLB cases.
+
+For all architectures, enable_soft_offline controls whether to soft offline
+memory pages. When setting to 1, kernel attempts to soft offline the pages
+whenever it thinks needed. When setting to 0, kernel returns EOPNOTSUPP to
+the request to soft offline the pages. Its default value is 1.
+
+It is worth mentioning that after setting enable_soft_offline to 0:
+- If RAS Correctable Errors Collector is running, its request to soft offline
+ pages will fail.
+- On ARM, the request to soft offline pages from GHES driver will fail.
+- On PARISC, the request to soft offline pages from Page Deallocation Table
+ will fail.
extfrag_threshold
=================
_
Patches currently in -mm which might be from jiaqiyan@xxxxxxxxxx are
mm-memory-failure-userspace-controls-soft-offlining-pages.patch
selftest-mm-test-enable_soft_offline-behaviors.patch
docs-mm-add-enable_soft_offline-sysctl.patch
