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SubjectRe: [PATCH 5/5] mm/memory_hotplug: Clean up node_states_check_changes_offline
Date
On 9/19/18 6:08 AM, Oscar Salvador wrote:
> From: Oscar Salvador <osalvador@suse.de>
>
> This patch, as the previous one, gets rid of the wrong if statements.
> While at it, I realized that the comments are sometimes very confusing,
> to say the least, and wrong.
> For example:
>
> ---
> zone_last = ZONE_MOVABLE;
>
> /*
> * check whether node_states[N_HIGH_MEMORY] will be changed
> * If we try to offline the last present @nr_pages from the node,
> * we can determind we will need to clear the node from
> * node_states[N_HIGH_MEMORY].
> */
>
> for (; zt <= zone_last; zt++)
> present_pages += pgdat->node_zones[zt].present_pages;
> if (nr_pages >= present_pages)
> arg->status_change_nid = zone_to_nid(zone);
> else
> arg->status_change_nid = -1;
> ---
>
> In case the node gets empry, it must be removed from N_MEMORY.
> We already check N_HIGH_MEMORY a bit above within the CONFIG_HIGHMEM
> ifdef code.
> Not to say that status_change_nid is for N_MEMORY, and not for
> N_HIGH_MEMORY.
>
> So I re-wrote some of the comments to what I think is better.
>
> Signed-off-by: Oscar Salvador <osalvador@suse.de>
> ---
> mm/memory_hotplug.c | 71 +++++++++++++++++++++--------------------------------
> 1 file changed, 28 insertions(+), 43 deletions(-)
>
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index ab3c1de18c5d..15ecf3d7a554 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1485,51 +1485,36 @@ static void node_states_check_changes_offline(unsigned long nr_pages,
> {
> struct pglist_data *pgdat = zone->zone_pgdat;
> unsigned long present_pages = 0;
> - enum zone_type zt, zone_last = ZONE_NORMAL;
> + enum zone_type zt;
>
> /*
> - * If we have HIGHMEM or movable node, node_states[N_NORMAL_MEMORY]
> - * contains nodes which have zones of 0...ZONE_NORMAL,
> - * set zone_last to ZONE_NORMAL.
> - *
> - * If we don't have HIGHMEM nor movable node,
> - * node_states[N_NORMAL_MEMORY] contains nodes which have zones of
> - * 0...ZONE_MOVABLE, set zone_last to ZONE_MOVABLE.
> + * Check whether node_states[N_NORMAL_MEMORY] will be changed.
> + * If the memory to be offline is within the range
> + * [0..ZONE_NORMAL], and it is the last present memory there,
> + * the zones in that range will become empty after the offlining,
> + * thus we can determine that we need to clear the node from
> + * node_states[N_NORMAL_MEMORY].
> */
> - if (N_MEMORY == N_NORMAL_MEMORY)
> - zone_last = ZONE_MOVABLE;
> -
> - /*
> - * check whether node_states[N_NORMAL_MEMORY] will be changed.
> - * If the memory to be offline is in a zone of 0...zone_last,
> - * and it is the last present memory, 0...zone_last will
> - * become empty after offline , thus we can determind we will
> - * need to clear the node from node_states[N_NORMAL_MEMORY].
> - */
> - for (zt = 0; zt <= zone_last; zt++)
> + for (zt = 0; zt <= ZONE_NORMAL; zt++)
> present_pages += pgdat->node_zones[zt].present_pages;
> - if (zone_idx(zone) <= zone_last && nr_pages >= present_pages)
> + if (zone_idx(zone) <= ZONE_NORMAL && nr_pages >= present_pages)
> arg->status_change_nid_normal = zone_to_nid(zone);
> else
> arg->status_change_nid_normal = -1;
>
> #ifdef CONFIG_HIGHMEM
> /*
> - * If we have movable node, node_states[N_HIGH_MEMORY]
> - * contains nodes which have zones of 0...ZONE_HIGHMEM,
> - * set zone_last to ZONE_HIGHMEM.
> - *
> - * If we don't have movable node, node_states[N_NORMAL_MEMORY]
> - * contains nodes which have zones of 0...ZONE_MOVABLE,
> - * set zone_last to ZONE_MOVABLE.
> + * node_states[N_HIGH_MEMORY] contains nodes which
> + * have normal memory or high memory.
> + * Here we add the present_pages belonging to ZONE_HIGHMEM.
> + * If the zone is within the range of [0..ZONE_HIGHMEM), and
> + * we determine that the zones in that range become empty,
> + * we need to clear the node for N_HIGH_MEMORY.
> */
> - zone_last = ZONE_HIGHMEM;
> - if (N_MEMORY == N_HIGH_MEMORY)
> - zone_last = ZONE_MOVABLE;
> + zt = ZONE_HIGHMEM;
> + present_pages += pgdat->node_zones[zt].present_pages;
>
> - for (; zt <= zone_last; zt++)
> - present_pages += pgdat->node_zones[zt].present_pages;
> - if (zone_idx(zone) <= zone_last && nr_pages >= present_pages)
> + if (zone_idx(zone) <= zt && nr_pages >= present_pages)
> arg->status_change_nid_high = zone_to_nid(zone);
> else
> arg->status_change_nid_high = -1;
> @@ -1542,18 +1527,18 @@ static void node_states_check_changes_offline(unsigned long nr_pages,
> #endif
>
> /*
> - * node_states[N_HIGH_MEMORY] contains nodes which have 0...ZONE_MOVABLE
> + * We have accounted the pages from [0..ZONE_NORMAL), and
> + * in case of CONFIG_HIGHMEM the pages from ZONE_HIGHMEM
> + * as well.
> + * Here we count the possible pages from ZONE_MOVABLE.
> + * If after having accounted all the pages, we see that the nr_pages
> + * to be offlined is over or equal to the accounted pages,
> + * we know that the node will become empty, and so, we can clear
> + * it for N_MEMORY as well.
> */
> - zone_last = ZONE_MOVABLE;
> + zt = ZONE_MOVABLE;
> + present_pages += pgdat->node_zones[zt].present_pages;
>
> - /*
> - * check whether node_states[N_HIGH_MEMORY] will be changed
> - * If we try to offline the last present @nr_pages from the node,
> - * we can determind we will need to clear the node from
> - * node_states[N_HIGH_MEMORY].
> - */
> - for (; zt <= zone_last; zt++)
> - present_pages += pgdat->node_zones[zt].present_pages;
> if (nr_pages >= present_pages)
> arg->status_change_nid = zone_to_nid(zone);
> else
>


A couple nits:

I would simplify this a little, initialize all fields at the beginning

arg->status_change_nid_normal = -1;
arg->status_change_nid_high = -1;
arg->status_change_nid = -1;

And remove all the elses, including ifdef else.

And remove:
zt = ZONE_HIGHMEM;
zt = ZONE_MOVABLE;

Use macros directly, lines are are still going to be under 80 chars.

Otherwise looks good.

Reviewed-by: Pavel Tatashin <pavel.tatashin@microsoft.com>

Pavel
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