Hi, Mike and Peter! On 6/9/22 20:52, Mike Kravetz wrote:
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>
Thanks for the patch. Applied. And thanks, Peter, for reviewing it! Cheers, Alex
---
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,
s/. /.\n/ But I fixed & amended.
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
-- Alejandro Colomar Linux man-pages comaintainer; http://www.kernel.org/doc/man-pages/ http://www.alejandro-colomar.es/
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