Re: [RFC] mm: show message when updating min_free_kbytes in thp

David Rientjes
2014-01-09T21:16:05Z

On Thu, 9 Jan 2014, Han Pingtian wrote:

> min_free_kbytes may be raised during THP's initialization. Sometimes,
> this will change the value being set by user. Showing message will
> clarify this confusion.
>
> Only show this message when changing the value set by user according to
> Michal Hocko's suggestion.
>
> Showing the old value of min_free_kbytes according to Dave Hansen's
> suggestion. This will give user the chance to restore old value of
> min_free_kbytes.
>
> Signed-off-by: Han Pingtian <hanpt@linux.vnet.ibm.com>
> ---
> mm/huge_memory.c | 9 ++++++++-
> mm/page_alloc.c | 2 +-
> 2 files changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 7de1bf8..e0e4e29 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -100,6 +100,7 @@ static struct khugepaged_scan khugepaged_scan = {
> .mm_head = LIST_HEAD_INIT(khugepaged_scan.mm_head),
> };
>
> +extern int user_min_free_kbytes;
>

We don't add extern declarations to .c files. How many other examples of
this can you find in mm/?

> static int set_recommended_min_free_kbytes(void)
> {
> @@ -130,8 +131,14 @@ static int set_recommended_min_free_kbytes(void)
> (unsigned long) nr_free_buffer_pages() / 20);
> recommended_min <<= (PAGE_SHIFT-10);
>
> - if (recommended_min > min_free_kbytes)
> + if (recommended_min > min_free_kbytes) {
> + if (user_min_free_kbytes >= 0)
> + pr_info("raising min_free_kbytes from %d to %lu "
> + "to help transparent hugepage allocations\n",
> + min_free_kbytes, recommended_min);
> +
> min_free_kbytes = recommended_min;
> + }
> setup_per_zone_wmarks();
> return 0;
> }

Does this even ever trigger since set_recommended_min_free_kbytes() is
called via late_initcall()?