| Message ID | 20240624163348.1751454-5-jiaqiyan@google.com |
|---|---|
| State | Superseded |
| Headers | show |
| Series | Userspace controls soft-offline pages | expand |
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, > +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 > =================
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 @@ -36,6 +36,7 @@ Currently, these files are in /proc/sys/vm: - dirtytime_expire_seconds - dirty_writeback_centisecs - drop_caches +- enable_soft_offline - extfrag_threshold - highmem_is_dirtyable - hugetlb_shm_group @@ -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 + 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, 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 =================