From: Oscar Salvador <[email protected]>
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.
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.
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 <[email protected]>
---
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;
}
--
2.13.6
On Tue, 28 Aug 2018 23:01:58 +0200 Oscar Salvador <[email protected]> wrote:
> From: Oscar Salvador <[email protected]>
>
> 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 <[email protected]>
AuthorDate: Wed Dec 12 13:51:46 2012 -0800
Commit: Linus Torvalds <[email protected]>
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 <[email protected]>
> ---
> 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;
> }
On Tue, Aug 28, 2018 at 02:35:30PM -0700, Andrew Morton wrote:
> > First, we should only set N_HIGH_MEMORY in case we have
> > CONFIG_HIGHMEM.
>
> Why? Just a teeny optimization?
Hi Andrew,
Optimization was not really my point here, my point was to make
the code less subtle and more clear.
One may wonder why we set N_HIGH_MEMORY unconditionally when
__only__ CONFIG_HIGHMEM matters for this case, and why we set
N_NORMAL_MEMORY __only__ for CONFIG_HIGHMEM when we should not care
about that at all.
I do not really expect a big impact here, mainly because check_for_memory
is only being used during boot.
--
Oscar Salvador
SUSE L3
On 8/28/18 5:01 PM, Oscar Salvador wrote:
> From: Oscar Salvador <[email protected]>
>
> 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.
>
> 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.
> 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 <[email protected]>
> ---
> 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;
> }
>
I would re-write the above function like this:
static void check_for_memory(pg_data_t *pgdat, int nid)
{
enum zone_type zone_type;
for (zone_type = 0; zone_type < ZONE_MOVABLE; zone_type++) {
if (populated_zone(&pgdat->node_zones[zone_type])) {
node_set_state(nid, zone_type <= ZONE_NORMAL ?
N_NORMAL_MEMORY: N_HIGH_MEMORY);
break;
}
}
}
zone_type <= ZONE_MOVABLE - 1
is the same as:
zone_type < ZONE_MOVABLE
If zone > ZONE_NORMAL, it means that CONFIG_HIGHMEM is enabled, no need to check for it.
Pavel
On Thu, Aug 30, 2018 at 01:55:29AM +0000, Pasha Tatashin wrote:
> I would re-write the above function like this:
> static void check_for_memory(pg_data_t *pgdat, int nid)
> {
> enum zone_type zone_type;
>
> for (zone_type = 0; zone_type < ZONE_MOVABLE; zone_type++) {
> if (populated_zone(&pgdat->node_zones[zone_type])) {
> node_set_state(nid, zone_type <= ZONE_NORMAL ?
> N_NORMAL_MEMORY: N_HIGH_MEMORY);
> break;
> }
> }
> }
Hi Pavel,
the above would not work fine.
You set either N_NORMAL_MEMORY or N_HIGH_MEMORY, but a node can have both
types of memory at the same time (on CONFIG_HIGHMEM systems).
N_HIGH_MEMORY stands for regular or high memory
while N_NORMAL_MEMORY stands only for regular memory,
that is why we set it only in case the zone is <= ZONE_NORMAL.
> zone_type <= ZONE_MOVABLE - 1
> is the same as:
> zone_type < ZONE_MOVABLE
This makes sense.
--
Oscar Salvador
SUSE L3
On 8/31/18 8:24 AM, Oscar Salvador wrote:
> On Thu, Aug 30, 2018 at 01:55:29AM +0000, Pasha Tatashin wrote:
>> I would re-write the above function like this:
>> static void check_for_memory(pg_data_t *pgdat, int nid)
>> {
>> enum zone_type zone_type;
>>
>> for (zone_type = 0; zone_type < ZONE_MOVABLE; zone_type++) {
>> if (populated_zone(&pgdat->node_zones[zone_type])) {
>> node_set_state(nid, zone_type <= ZONE_NORMAL ?
>> N_NORMAL_MEMORY: N_HIGH_MEMORY);
>> break;
>> }
>> }
>> }
>
> Hi Pavel,
>
> the above would not work fine.
> You set either N_NORMAL_MEMORY or N_HIGH_MEMORY, but a node can have both
> types of memory at the same time (on CONFIG_HIGHMEM systems).
>
> N_HIGH_MEMORY stands for regular or high memory
> while N_NORMAL_MEMORY stands only for regular memory,
> that is why we set it only in case the zone is <= ZONE_NORMAL.
Hi Oscar,
Are you saying the code that is in mainline is broken? Because we set
node_set_state(nid, N_NORMAL_MEMORY); even on node with N_HIGH_MEMORY:
6826 if (N_NORMAL_MEMORY != N_HIGH_MEMORY &&
6827 zone_type <= ZONE_NORMAL)
6828 node_set_state(nid, N_NORMAL_MEMORY);
Thank you,
Pavel
On Fri, Aug 31, 2018 at 02:04:59PM +0000, Pasha Tatashin wrote:
> Are you saying the code that is in mainline is broken? Because we set
> node_set_state(nid, N_NORMAL_MEMORY); even on node with N_HIGH_MEMORY:
>
> 6826 if (N_NORMAL_MEMORY != N_HIGH_MEMORY &&
> 6827 zone_type <= ZONE_NORMAL)
> 6828 node_set_state(nid, N_NORMAL_MEMORY);
Yes, and that is fine. Although the curent code is subtle for the reasons
I expplained in the changelog.
What I am saying is that the code you suggested would not work
because your code either sets N_NORMAL_MEMORY or N_HIGH_MEMORY and then
breaks the loop.
That is wrong because when we are on a CONFIG_HIGHMEM system,
it can happen that we have a node with both types, so we have to set
both types of memory.
N_HIGH_MEMORY, and N_NORMAL_MEMORY if the zone is <= ZONE_NORMAL.
Thanks
--
Oscar Salvador
SUSE L3