4 files changed, 58 insertions, 12 deletions
diff --git a/Documentation/filesystems/9p.rst b/Documentation/filesystems/9p.rst
index 3078f3c9256a..be3504ca034a 100644
--- a/Documentation/filesystems/9p.rst
+++ b/Documentation/filesystems/9p.rst
@@ -40,7 +40,7 @@ For remote file server::
 
 	mount -t 9p 10.10.1.2 /mnt/9
 
-For Plan 9 From User Space applications (http://swtch.com/plan9)::
+For Plan 9 From User Space applications (https://9fans.github.io/plan9port/)::
 
 	mount -t 9p `namespace`/acme /mnt/9 -o trans=unix,uname=$USER
 
@@ -165,8 +165,8 @@ Options
 		do not necessarily validate cached values on the server.  In other
 		words changes on the server are not guaranteed to be reflected
 		on the client system.  Only use this mode of operation if you
-		have an exclusive mount and the server will modify the filesystem
-		underneath you.
+		have an exclusive mount and the server will not modify the
+		filesystem underneath you.
 
   debug=n	specifies debug level.  The debug level is a bitmask.
 
diff --git a/Documentation/filesystems/dax.rst b/Documentation/filesystems/dax.rst
index 719e90f1988e..08dd5e254cc5 100644
--- a/Documentation/filesystems/dax.rst
+++ b/Documentation/filesystems/dax.rst
@@ -207,7 +207,6 @@ implement direct_access.
 
 These block devices may be used for inspiration:
 - brd: RAM backed block device driver
-- dcssblk: s390 dcss block device driver
 - pmem: NVDIMM persistent memory driver
 
 
diff --git a/Documentation/filesystems/nfs/reexport.rst b/Documentation/filesystems/nfs/reexport.rst
index ff9ae4a46530..044be965d75e 100644
--- a/Documentation/filesystems/nfs/reexport.rst
+++ b/Documentation/filesystems/nfs/reexport.rst
@@ -26,9 +26,13 @@ Reboot recovery
 ---------------
 
 The NFS protocol's normal reboot recovery mechanisms don't work for the
-case when the reexport server reboots.  Clients will lose any locks
-they held before the reboot, and further IO will result in errors.
-Closing and reopening files should clear the errors.
+case when the reexport server reboots because the source server has not
+rebooted, and so it is not in grace.  Since the source server is not in
+grace, it cannot offer any guarantees that the file won't have been
+changed between the locks getting lost and any attempt to recover them.
+The same applies to delegations and any associated locks.  Clients are
+not allowed to get file locks or delegations from a reexport server, any
+attempts will fail with operation not supported.
 
 Filehandle limits
 -----------------
diff --git a/Documentation/filesystems/proc.rst b/Documentation/filesystems/proc.rst
index 09f0aed5a08b..2a17865dfe39 100644
--- a/Documentation/filesystems/proc.rst
+++ b/Documentation/filesystems/proc.rst
@@ -128,6 +128,16 @@ process running on the system, which is named after the process ID (PID).
 The link  'self'  points to  the process reading the file system. Each process
 subdirectory has the entries listed in Table 1-1.
 
+A process can read its own information from /proc/PID/* with no extra
+permissions. When reading /proc/PID/* information for other processes, reading
+process is required to have either CAP_SYS_PTRACE capability with
+PTRACE_MODE_READ access permissions, or, alternatively, CAP_PERFMON
+capability. This applies to all read-only information like `maps`, `environ`,
+`pagemap`, etc. The only exception is `mem` file due to its read-write nature,
+which requires CAP_SYS_PTRACE capabilities with more elevated
+PTRACE_MODE_ATTACH permissions; CAP_PERFMON capability does not grant access
+to /proc/PID/mem for other processes.
+
 Note that an open file descriptor to /proc/<pid> or to any of its
 contained files or subdirectories does not prevent <pid> being reused
 for some other process in the event that <pid> exits. Operations on
@@ -502,9 +512,25 @@ process, its PSS will be 1500.  "Pss_Dirty" is the portion of PSS which
 consists of dirty pages.  ("Pss_Clean" is not included, but it can be
 calculated by subtracting "Pss_Dirty" from "Pss".)
 
-Note that even a page which is part of a MAP_SHARED mapping, but has only
-a single pte mapped, i.e.  is currently used by only one process, is accounted
-as private and not as shared.
+Traditionally, a page is accounted as "private" if it is mapped exactly once,
+and a page is accounted as "shared" when mapped multiple times, even when
+mapped in the same process multiple times. Note that this accounting is
+independent of MAP_SHARED.
+
+In some kernel configurations, the semantics of pages part of a larger
+allocation (e.g., THP) can differ: a page is accounted as "private" if all
+pages part of the corresponding large allocation are *certainly* mapped in the
+same process, even if the page is mapped multiple times in that process. A
+page is accounted as "shared" if any page page of the larger allocation
+is *maybe* mapped in a different process. In some cases, a large allocation
+might be treated as "maybe mapped by multiple processes" even though this
+is no longer the case.
+
+Some kernel configurations do not track the precise number of times a page part
+of a larger allocation is mapped. In this case, when calculating the PSS, the
+average number of mappings per page in this larger allocation might be used
+as an approximation for the number of mappings of a page. The PSS calculation
+will be imprecise in this case.
 
 "Referenced" indicates the amount of memory currently marked as referenced or
 accessed.
@@ -686,6 +712,11 @@ Where:
 node locality page counters (N0 == node0, N1 == node1, ...) and the kernel page
 size, in KB, that is backing the mapping up.
 
+Note that some kernel configurations do not track the precise number of times
+a page part of a larger allocation (e.g., THP) is mapped. In these
+configurations, "mapmax" might corresponds to the average number of mappings
+per page in such a larger allocation instead.
+
 1.2 Kernel data
 ---------------
 
@@ -1060,6 +1091,8 @@ Example output. You may not have all of these fields.
     FilePmdMapped:         0 kB
     CmaTotal:              0 kB
     CmaFree:               0 kB
+    Unaccepted:            0 kB
+    Balloon:               0 kB
     HugePages_Total:       0
     HugePages_Free:        0
     HugePages_Rsvd:        0
@@ -1132,9 +1165,15 @@ Dirty
 Writeback
               Memory which is actively being written back to the disk
 AnonPages
-              Non-file backed pages mapped into userspace page tables
+              Non-file backed pages mapped into userspace page tables. Note that
+              some kernel configurations might consider all pages part of a
+              larger allocation (e.g., THP) as "mapped", as soon as a single
+              page is mapped.
 Mapped
-              files which have been mmapped, such as libraries
+              files which have been mmapped, such as libraries. Note that some
+              kernel configurations might consider all pages part of a larger
+              allocation (e.g., THP) as "mapped", as soon as a single page is
+              mapped.
 Shmem
               Total memory used by shared memory (shmem) and tmpfs
 KReclaimable
@@ -1228,6 +1267,10 @@ CmaTotal
               Memory reserved for the Contiguous Memory Allocator (CMA)
 CmaFree
               Free remaining memory in the CMA reserves
+Unaccepted
+              Memory that has not been accepted by the guest
+Balloon
+              Memory returned to Host by VM Balloon Drivers
 HugePages_Total, HugePages_Free, HugePages_Rsvd, HugePages_Surp, Hugepagesize, Hugetlb
               See Documentation/admin-guide/mm/hugetlbpage.rst.
 DirectMap4k, DirectMap2M, DirectMap1G