Re: [PATCH man-pages 1/4] madvise.2: update THP file/shmem documentation for +5.4

[Alex Colomar <alx.manpages@gmail.com>]

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Hi Zach,

On 10/17/22 19:55, Zach OKeefe wrote:
> From: Zach O'Keefe <zokeefe@google.com>
> 
> Since Linux 5.4, Transparent Huge Pages now support both file-backed
> memory and shmem memory. Update MADV_HUGEPAGE advice description to
> reflect this.
> 
> Additionally, expand the description of requirements for memory to be
> considered eligible for THP: alignment / mapping requirements, VMA
> flags, prctl(2) settings, inode status, etc.
> 
> Signed-off-by: Zach O'Keefe <zokeefe@google.com>
> ---
>   man2/madvise.2 | 37 ++++++++++++++++++++++++++++++++++---
>   1 file changed, 34 insertions(+), 3 deletions(-)
> 
> diff --git a/man2/madvise.2 b/man2/madvise.2
> index 81cce56af..e14e0f7fb 100644
> --- a/man2/madvise.2
> +++ b/man2/madvise.2
> @@ -320,8 +320,6 @@ Enable Transparent Huge Pages (THP) for pages in the range specified by
>   .I addr
>   and
>   .IR length .
> -Currently, Transparent Huge Pages work only with private anonymous pages (see
> -.BR mmap (2)).
>   The kernel will regularly scan the areas marked as huge page candidates
>   to replace them with huge pages.
>   The kernel will also allocate huge pages directly when the region is
> @@ -354,12 +352,45 @@ an access pattern that the developer knows in advance won't risk
>   to increase the memory footprint of the application when transparent
>   hugepages are enabled.
>   .IP
> +.\" commit 99cb0dbd47a15d395bf3faa78dc122bc5efe3fc0
> +Since Linux 5.4,
> +automatic scan of eligible areas and replacement by huge pages works with
> +private anonymous pages (see
> +.BR mmap (2)),
> +shmem-backed pages (including tmpfs (see
> +.BR tmpfs (5)),

I think here's missing a closing parenthesis.  Please check.  Maybe you 
prefer combining em dashes or commas with parentheses to improve 
visually discerning subclauses.

Cheers,
Alex

> +and file-backed pages.
> +For all memory types,
> +memory may only be replaced by huge pages on hugepage-aligned boundaries.
> +For file-mapped memory (including tmpfs) the mapping must also be naturally
> +hugepage-aligned within the file.
> +Additionally,
> +for file-backed (not tmpfs) memory,
> +the file must not be open for write and the mapping must be executable.
> +.IP

[...]

-- 
<http://www.alejandro-colomar.es/>


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