On 26/07/2024 09:28, Barry Song wrote:
> From: Barry Song <v-songbaohua@xxxxxxxx>
>
> khugepaged will be automatically started when PMD-sized THP is enabled
> (either of the per-size anon control or the top-level control are set
> to "always" or "madvise"), and it'll be automatically shutdown when
> PMD-sized THP is disabled (when both the per-size anon control and the
> top-level control are "never").
>
> It seems unnecessary to call start_stop_khugepaged() for non-PMD THP,
> as it would only waste CPU time.
>
> Cc: Lance Yang <ioworker0@xxxxxxxxx>
> Cc: Ryan Roberts <ryan.roberts@xxxxxxx>
> Cc: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
> Cc: David Hildenbrand <david@xxxxxxxxxx>
> Cc: Yang Shi <shy828301@xxxxxxxxx>
> Cc: Zi Yan <ziy@xxxxxxxxxx>
> Signed-off-by: Barry Song <v-songbaohua@xxxxxxxx>
> ---
> mm/huge_memory.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 41460847988c..bd365e35acf7 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -514,7 +514,7 @@ static ssize_t thpsize_enabled_store(struct kobject *kobj,
> } else
> ret = -EINVAL;
>
> - if (ret > 0) {
> + if (ret > 0 && order == HPAGE_PMD_ORDER) {
> int err;
>
> err = start_stop_khugepaged();
Personally I see this as a bit of a layering violation; its
start_stop_khugepaged() that should decide the policy for when to start and stop
the daemon. thpsize_enabled_store() should just be calling
start_stop_khugepaged() to notify that something potentially pertinent to the a
policy decision has changed.
And I don't think this should be a hot path; I'd expect the global thp size
configuration to be set at boot and remain pretty static. Do you have evidence
to the contrary?
