On Tue, 28 Aug 2018 23:01:58 +0200 Oscar Salvador <osalvador@xxxxxxxxxxxxxxxxxx> wrote:
> From: Oscar Salvador <osalvador@xxxxxxx>
>
> check_for_memory looks a bit confusing.
> First of all, we have this:
>
> if (N_MEMORY == N_NORMAL_MEMORY)
> return;
>
> Checking the ENUM declaration, looks like N_MEMORY canot be equal to
> N_NORMAL_MEMORY.
> I could not find where N_MEMORY is set to N_NORMAL_MEMORY, or the other
> way around either, so unless I am missing something, this condition
> will never evaluate to true.
> It makes sense to get rid of it.
Added by
commit 4b0ef1fe8a626f0ba7f649764f979d0dc9eab86b
Author: Lai Jiangshan <laijs@xxxxxxxxxxxxxx>
AuthorDate: Wed Dec 12 13:51:46 2012 -0800
Commit: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
CommitDate: Wed Dec 12 17:38:33 2012 -0800
page_alloc: use N_MEMORY instead N_HIGH_MEMORY change the node_states initia
lization
Let's cc Lai Jiangshan, see if he can remmeber the reasoning.
But yes, it does look like im-not-sure-whats-going-on-here
defensiveness.
> Moving forward, the operations whithin the loop look a bit confusing
> as well.
>
> We set N_HIGH_MEMORY unconditionally, and then we set N_NORMAL_MEMORY
> in case we have CONFIG_HIGHMEM (N_NORMAL_MEMORY != N_HIGH_MEMORY)
> and zone <= ZONE_NORMAL.
> (N_HIGH_MEMORY falls back to N_NORMAL_MEMORY on !CONFIG_HIGHMEM systems,
> and that is why we can just go ahead and set N_HIGH_MEMORY unconditionally)
>
> Although this works, it is a bit subtle.
>
> I think that this could be easier to follow:
>
> First, we should only set N_HIGH_MEMORY in case we have
> CONFIG_HIGHMEM.
Why? Just a teeny optimization?
> And then we should set N_NORMAL_MEMORY in case zone <= ZONE_NORMAL,
> without further checking whether we have CONFIG_HIGHMEM or not.
>
> Signed-off-by: Oscar Salvador <osalvador@xxxxxxx>
> ---
> mm/page_alloc.c | 9 +++------
> 1 file changed, 3 insertions(+), 6 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 839e0cc17f2c..6aa947f9e614 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -6819,15 +6819,12 @@ static void check_for_memory(pg_data_t *pgdat, int nid)
> {
> enum zone_type zone_type;
>
> - if (N_MEMORY == N_NORMAL_MEMORY)
> - return;
> -
> for (zone_type = 0; zone_type <= ZONE_MOVABLE - 1; zone_type++) {
> struct zone *zone = &pgdat->node_zones[zone_type];
> if (populated_zone(zone)) {
> - node_set_state(nid, N_HIGH_MEMORY);
> - if (N_NORMAL_MEMORY != N_HIGH_MEMORY &&
> - zone_type <= ZONE_NORMAL)
> + if (IS_ENABLED(CONFIG_HIGHMEM))
> + node_set_state(nid, N_HIGH_MEMORY);
> + if (zone_type <= ZONE_NORMAL)
> node_set_state(nid, N_NORMAL_MEMORY);
> break;
> }
