Clarify that madvise only works on full pages, and remove references
to 'bytes'.
Update MADV_DONTNEED and MADV_REMOVE sections to remove notes that
HugeTLB mappings are not supported. Indicate the releases when they
were first supported as well as alignment restrictions.
Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Acked-by: Peter Xu <peterx@xxxxxxxxxx>
---
v3 -> v4 Formatting updates (Alex)
v2 -> v3 Rebased on man-pages-5.19-rc1. Minor change to wording for
sunsequent access of data after MADV_REMOVE.
v1 -> v2 Added releases when Huge TLB support was added and moved
alignment requirements to corresponding section. (Peter)
man2/madvise.2 | 33 +++++++++++++++++++++++----------
1 file changed, 23 insertions(+), 10 deletions(-)
diff --git a/man2/madvise.2 b/man2/madvise.2
index 2a8f1cd0a..7fc184e20 100644
--- a/man2/madvise.2
+++ b/man2/madvise.2
@@ -44,9 +44,14 @@ system call is used to give advice or directions to the kernel
about the address range beginning at address
.I addr
and with size
+.IR length .
+.BR madvise ()
+only operates on whole pages, therefore
+.I addr
+must be page-aligned.
+The value of
.I length
-bytes.
-In most cases,
+is rounded up to a multiple of page size. In most cases,
the goal of such advice is to improve system or application performance.
.PP
Initially, the system call supported a set of "conventional"
@@ -126,7 +131,7 @@ The resident set size (RSS) of the calling process will be immediately
reduced however.
.IP
.B MADV_DONTNEED
-cannot be applied to locked pages, Huge TLB pages, or
+cannot be applied to locked pages, or
.B VM_PFNMAP
pages.
(Pages marked with the kernel-internal
@@ -136,6 +141,12 @@ flag are special memory areas that are not managed
by the virtual memory subsystem.
Such pages are typically created by device drivers that
map the pages into user space.)
+.IP
+Support for Huge TLB pages was added in Linux v5.18.
+Addresses within a mapping backed by Huge TLB pages must be aligned
+to the underlying Huge TLB page size,
+and the range length is rounded up
+to a multiple of the underlying Huge TLB page size.
.\"
.\" ======================================================================
.\"
@@ -153,24 +164,24 @@ Note that some of these operations change the semantics of memory accesses.
.\" commit f6b3ec238d12c8cc6cc71490c6e3127988460349
Free up a given range of pages
and its associated backing store.
-This is equivalent to punching a hole in the corresponding byte
+This is equivalent to punching a hole in the corresponding
range of the backing store (see
.BR fallocate (2)).
Subsequent accesses in the specified address range will see
-bytes containing zero.
+data with a value of zero.
.\" Databases want to use this feature to drop a section of their
.\" bufferpool (shared memory segments) - without writing back to
.\" disk/swap space. This feature is also useful for supporting
.\" hot-plug memory on UML.
.IP
The specified address range must be mapped shared and writable.
-This flag cannot be applied to locked pages, Huge TLB pages, or
+This flag cannot be applied to locked pages, or
.B VM_PFNMAP
pages.
.IP
In the initial implementation, only
.BR tmpfs (5)
-was supported
+supported
.BR MADV_REMOVE ;
but since Linux 3.5,
.\" commit 3f31d07571eeea18a7d34db9af21d2285b807a17
@@ -179,10 +190,12 @@ any filesystem which supports the
.B FALLOC_FL_PUNCH_HOLE
mode also supports
.BR MADV_REMOVE .
-Hugetlbfs fails with the error
-.B EINVAL
-and other filesystems fail with the error
+Filesystems which do not support
+.B MADV_REMOVE
+fail with the error
.BR EOPNOTSUPP .
+.IP
+Support for the Huge TLB filesystem was added in Linux v4.3.
.TP
.BR MADV_DONTFORK " (since Linux 2.6.16)"
.\" commit f822566165dd46ff5de9bf895cfa6c51f53bb0c4
--
2.35.3
