Re: [PATCH v2 2/3] mm/memory_hotplug: document why shuffle_zone() is relevant
On 23.06.20 23:15, Dan Williams wrote:
> On Mon, Jun 22, 2020 at 12:28 AM David Hildenbrand wrote:
>>
>> On 20.06.20 03:41, Dan Williams wrote:
>>> On Fri, Jun 19, 2020 at 6:00 AM David Hildenbrand wrote:
It's not completely obvious why we have to shuffle the complete zone, as
some sort of shuffling is already performed when onlining pages via
__free_one_page(), placing MAX_ORDER-1 pages either to the head or the tail
of the freelist. Let's document why we have to shuffle the complete zone
when exposing larger, contiguous physical memory areas to the buddy.
>>>
>>> How about?
>>>
>>> Fixes: e900a918b098 ("mm: shuffle initial free memory to improve
>>> memory-side-cache utilization")
>>>
>>> ...just like Patch1 since that original commit was missing the proper
>>> commentary in the code?
>>
>> Hmm, mixed feelings. I (working for a distributor :) ) prefer fixes tags
>> for actual BUGs, as described in
>>
>> Documentation/process/submitting-patches.rst: "If your patch fixes a bug
>> in a specific commit, e.g. you found an issue using ``git bisect``,
>> please use the 'Fixes:' tag with the first 12 characters" ...
>>
>> So unless there are strong feelings, I'll not add a fixes tag (although
>> I agree, that it should have been contained in the original commit).
>
> It doesn't need to be "Fixes", but how about at least mentioning the
> original commit as a breadcrumb so that some future "git blame"
> archaeology effort is streamlined.
>
Makes sense, I'll mention it as
It's not completely obvious why we have to shuffle the complete zone (
introduced in commit e900a918b098 ("mm: shuffle initial free memory to
...
thanks!
--
Thanks,
David / dhildenb
Re: [PATCH v2 2/3] mm/memory_hotplug: document why shuffle_zone() is relevant
On Mon, Jun 22, 2020 at 12:28 AM David Hildenbrand wrote:
>
> On 20.06.20 03:41, Dan Williams wrote:
> > On Fri, Jun 19, 2020 at 6:00 AM David Hildenbrand wrote:
> >>
> >> It's not completely obvious why we have to shuffle the complete zone, as
> >> some sort of shuffling is already performed when onlining pages via
> >> __free_one_page(), placing MAX_ORDER-1 pages either to the head or the tail
> >> of the freelist. Let's document why we have to shuffle the complete zone
> >> when exposing larger, contiguous physical memory areas to the buddy.
> >>
> >
> > How about?
> >
> > Fixes: e900a918b098 ("mm: shuffle initial free memory to improve
> > memory-side-cache utilization")
> >
> > ...just like Patch1 since that original commit was missing the proper
> > commentary in the code?
>
> Hmm, mixed feelings. I (working for a distributor :) ) prefer fixes tags
> for actual BUGs, as described in
>
> Documentation/process/submitting-patches.rst: "If your patch fixes a bug
> in a specific commit, e.g. you found an issue using ``git bisect``,
> please use the 'Fixes:' tag with the first 12 characters" ...
>
> So unless there are strong feelings, I'll not add a fixes tag (although
> I agree, that it should have been contained in the original commit).
It doesn't need to be "Fixes", but how about at least mentioning the
original commit as a breadcrumb so that some future "git blame"
archaeology effort is streamlined.
Re: [PATCH v2 2/3] mm/memory_hotplug: document why shuffle_zone() is relevant
On Fri 19-06-20 14:59:21, David Hildenbrand wrote: > It's not completely obvious why we have to shuffle the complete zone, as > some sort of shuffling is already performed when onlining pages via > __free_one_page(), placing MAX_ORDER-1 pages either to the head or the tail > of the freelist. Let's document why we have to shuffle the complete zone > when exposing larger, contiguous physical memory areas to the buddy. > > Cc: Andrew Morton > Cc: Alexander Duyck > Cc: Dan Williams > Cc: Michal Hocko > Signed-off-by: David Hildenbrand OK, this is an improvement. I would still prefer to have this claim backed by some numbers but it seems we are not going to get any so we can at least pretend to try as hard as possible especially when this is not a hot path. Acked-by: Michal Hocko > --- > mm/memory_hotplug.c | 8 > 1 file changed, 8 insertions(+) > > diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c > index 9b34e03e730a4..a0d81d404823d 100644 > --- a/mm/memory_hotplug.c > +++ b/mm/memory_hotplug.c > @@ -822,6 +822,14 @@ int __ref online_pages(unsigned long pfn, unsigned long > nr_pages, > zone->zone_pgdat->node_present_pages += onlined_pages; > pgdat_resize_unlock(zone->zone_pgdat, &flags); > > + /* > + * When exposing larger, physically contiguous memory areas to the > + * buddy, shuffling in the buddy (when freeing onlined pages, putting > + * them either to the head or the tail of the freelist) is only helpful > + * for mainining the shuffle, but not for creating the initial shuffle. > + * Shuffle the whole zone to make sure the just onlined pages are > + * properly distributed across the whole freelist. > + */ > shuffle_zone(zone); > > node_states_set_node(nid, &arg); > -- > 2.26.2 -- Michal Hocko SUSE Labs
Re: [PATCH v2 2/3] mm/memory_hotplug: document why shuffle_zone() is relevant
On 20.06.20 03:41, Dan Williams wrote:
> On Fri, Jun 19, 2020 at 6:00 AM David Hildenbrand wrote:
>>
>> It's not completely obvious why we have to shuffle the complete zone, as
>> some sort of shuffling is already performed when onlining pages via
>> __free_one_page(), placing MAX_ORDER-1 pages either to the head or the tail
>> of the freelist. Let's document why we have to shuffle the complete zone
>> when exposing larger, contiguous physical memory areas to the buddy.
>>
>
> How about?
>
> Fixes: e900a918b098 ("mm: shuffle initial free memory to improve
> memory-side-cache utilization")
>
> ...just like Patch1 since that original commit was missing the proper
> commentary in the code?
Hmm, mixed feelings. I (working for a distributor :) ) prefer fixes tags
for actual BUGs, as described in
Documentation/process/submitting-patches.rst: "If your patch fixes a bug
in a specific commit, e.g. you found an issue using ``git bisect``,
please use the 'Fixes:' tag with the first 12 characters" ...
So unless there are strong feelings, I'll not add a fixes tag (although
I agree, that it should have been contained in the original commit).
>> Cc: Andrew Morton
>> Cc: Alexander Duyck
>> Cc: Dan Williams
>> Cc: Michal Hocko
>> Signed-off-by: David Hildenbrand
>> ---
>> mm/memory_hotplug.c | 8
>> 1 file changed, 8 insertions(+)
>>
>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
>> index 9b34e03e730a4..a0d81d404823d 100644
>> --- a/mm/memory_hotplug.c
>> +++ b/mm/memory_hotplug.c
>> @@ -822,6 +822,14 @@ int __ref online_pages(unsigned long pfn, unsigned long
>> nr_pages,
>> zone->zone_pgdat->node_present_pages += onlined_pages;
>> pgdat_resize_unlock(zone->zone_pgdat, &flags);
>>
>> + /*
>> +* When exposing larger, physically contiguous memory areas to the
>> +* buddy, shuffling in the buddy (when freeing onlined pages, putting
>> +* them either to the head or the tail of the freelist) is only
>> helpful
>> +* for mainining the shuffle, but not for creating the initial
>> shuffle.
>
> s/mainining/maintaining/
Huh, what went wrong there :) Thanks!
--
Thanks,
David / dhildenb
Re: [PATCH v2 2/3] mm/memory_hotplug: document why shuffle_zone() is relevant
On Fri, Jun 19, 2020 at 6:00 AM David Hildenbrand wrote:
>
> It's not completely obvious why we have to shuffle the complete zone, as
> some sort of shuffling is already performed when onlining pages via
> __free_one_page(), placing MAX_ORDER-1 pages either to the head or the tail
> of the freelist. Let's document why we have to shuffle the complete zone
> when exposing larger, contiguous physical memory areas to the buddy.
>
How about?
Fixes: e900a918b098 ("mm: shuffle initial free memory to improve
memory-side-cache utilization")
...just like Patch1 since that original commit was missing the proper
commentary in the code?
> Cc: Andrew Morton
> Cc: Alexander Duyck
> Cc: Dan Williams
> Cc: Michal Hocko
> Signed-off-by: David Hildenbrand
> ---
> mm/memory_hotplug.c | 8
> 1 file changed, 8 insertions(+)
>
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 9b34e03e730a4..a0d81d404823d 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -822,6 +822,14 @@ int __ref online_pages(unsigned long pfn, unsigned long
> nr_pages,
> zone->zone_pgdat->node_present_pages += onlined_pages;
> pgdat_resize_unlock(zone->zone_pgdat, &flags);
>
> + /*
> +* When exposing larger, physically contiguous memory areas to the
> +* buddy, shuffling in the buddy (when freeing onlined pages, putting
> +* them either to the head or the tail of the freelist) is only
> helpful
> +* for mainining the shuffle, but not for creating the initial
> shuffle.
s/mainining/maintaining/
> +* Shuffle the whole zone to make sure the just onlined pages are
> +* properly distributed across the whole freelist.
> +*/
> shuffle_zone(zone);
>
> node_states_set_node(nid, &arg);
Other than the above minor fixups you can add:
Acked-by: Dan Williams
[PATCH v2 2/3] mm/memory_hotplug: document why shuffle_zone() is relevant
It's not completely obvious why we have to shuffle the complete zone, as some sort of shuffling is already performed when onlining pages via __free_one_page(), placing MAX_ORDER-1 pages either to the head or the tail of the freelist. Let's document why we have to shuffle the complete zone when exposing larger, contiguous physical memory areas to the buddy. Cc: Andrew Morton Cc: Alexander Duyck Cc: Dan Williams Cc: Michal Hocko Signed-off-by: David Hildenbrand --- mm/memory_hotplug.c | 8 1 file changed, 8 insertions(+) diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c index 9b34e03e730a4..a0d81d404823d 100644 --- a/mm/memory_hotplug.c +++ b/mm/memory_hotplug.c @@ -822,6 +822,14 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages, zone->zone_pgdat->node_present_pages += onlined_pages; pgdat_resize_unlock(zone->zone_pgdat, &flags); + /* +* When exposing larger, physically contiguous memory areas to the +* buddy, shuffling in the buddy (when freeing onlined pages, putting +* them either to the head or the tail of the freelist) is only helpful +* for mainining the shuffle, but not for creating the initial shuffle. +* Shuffle the whole zone to make sure the just onlined pages are +* properly distributed across the whole freelist. +*/ shuffle_zone(zone); node_states_set_node(nid, &arg); -- 2.26.2
