On Tue, Jun 25, 2024 at 5:02 PM Randy Dunlap rdunlap@infradead.org wrote:
Hi--
On 6/24/24 9:33 AM, Jiaqi Yan wrote:
Add the documentation for soft offline behaviors / costs, and what the new enable_soft_offline sysctl is for.
Acked-by: Oscar Salvador osalvador@suse.de
Signed-off-by: Jiaqi Yan jiaqiyan@google.com
Documentation/admin-guide/sysctl/vm.rst | 32 +++++++++++++++++++++++++ 1 file changed, 32 insertions(+)
diff --git a/Documentation/admin-guide/sysctl/vm.rst b/Documentation/admin-guide/sysctl/vm.rst index e86c968a7a0e..71463a7b3e2a 100644 --- a/Documentation/admin-guide/sysctl/vm.rst +++ b/Documentation/admin-guide/sysctl/vm.rst @@ -267,6 +268,37 @@ 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
Use only one space after the comma ...................^
- 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
When set to 1,+whenever it thinks needed. When setting to 0, kernel returns EOPNOTSUPP to
When set to 0,
Thanks Randy! I will fix these 3 nits in v6.
+the request to soft offline the pages. Its default value is 1.
+It is worth mentioning that after setting enable_soft_offline to 0, the +following requests to soft offline pages will not be performed: +- Request to soft offline pages from RAS Correctable Errors Collector. +- On ARM, the request to soft offline pages from GHES driver. +- On PARISC, the request to soft offline pages from Page Deallocation Table.
extfrag_threshold
-- ~Randy