Re: [PATCH v2] madvise.2: Clarify addr/length and update hugetlb support

[David Hildenbrand <david@redhat.com>]

On 26.05.22 20:09, 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@oracle.com>
> ---

BTW, the git repository [1] was last updated 2021-09-02. One of my
patches [2] was apparently picked up (reply via mail) but doesn't appear
in that repository.

Is the project currently dead/unmaintained or am I just staring at the
wrong repository?

[1] https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git
[2] https://lkml.kernel.org/r/20210823120645.8223-1-david@redhat.com

> v1 -> v2 Added releases when Huge TLB support was added and moved
> 	alignment requirements to corresponding section.  (Peter)
> 
>  man2/madvise.2 | 31 +++++++++++++++++++++----------
>  1 file changed, 21 insertions(+), 10 deletions(-)
> 
> diff --git a/man2/madvise.2 b/man2/madvise.2
> index f1f384c0c..50686e7e3 100644
> --- a/man2/madvise.2
> +++ b/man2/madvise.2
> @@ -61,9 +61,13 @@ 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"
> @@ -143,7 +147,7 @@ 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
>  .BR VM_PFNMAP
>  pages.
>  (Pages marked with the kernel-internal
> @@ -153,6 +157,11 @@ 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.
>  .\"
>  .\" ======================================================================
>  .\"
> @@ -170,24 +179,24 @@ 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.
> +pages containing 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
>  .BR 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
> @@ -196,10 +205,12 @@ any filesystem which supports the
>  .BR FALLOC_FL_PUNCH_HOLE
>  mode also supports
>  .BR MADV_REMOVE .
> -Hugetlbfs fails with the error
> -.BR EINVAL
> -and other filesystems fail with the error
> +Filesystems which do not support
> +.BR MADV_REMOVE
> +fail with the error
>  .BR EOPNOTSUPP .
> +.IP
> +Support for Huge TLB filesystem was added in Linux v4.3.
>  .TP
>  .BR MADV_DONTFORK " (since Linux 2.6.16)"
>  .\" commit f822566165dd46ff5de9bf895cfa6c51f53bb0c4


-- 
Thanks,

David / dhildenb