Re: [PATCH v8] mm/page_alloc.c: memory_hotplug: free pages as higher order

[Arun KS]

On 2019-01-09 21:47, Alexander Duyck wrote:
> On Wed, 2019-01-09 at 16:43 +0530, Arun KS wrote:
> > When freeing pages are done with higher order, time spent on 
> > coalescing
> > pages by buddy allocator can be reduced.  With section size of 256MB, 
> > hot
> > add latency of a single section shows improvement from 50-60 ms to 
> > less
> > than 1 ms, hence improving the hot add latency by 60 times.  Modify
> > external providers of online callback to align with the change.
> >
> > Signed-off-by: Arun KS <arunks@xxxxxxxxxxxxxx>
> > Acked-by: Michal Hocko <mhocko@xxxxxxxx>
> > Reviewed-by: Oscar Salvador <osalvador@xxxxxxx>
> > ---
> > Changes since v7:
> > - Rebased to 5.0-rc1.
> > - Fixed onlined_pages accounting.
> > - Added comment for return value of online_page_callback.
> > - Renamed xen_bring_pgs_online to xen_online_pages.
>
> As far as the renaming you should try to be consistent. If you aren't
> going to rename generic_online_page or hv_online_page I wouldn't bother
> with renaming xen_online_page. I would stick with the name
> xen_online_page since it is a single high order page that you are
> freeing.

Sure. I ll fix them.

> > Changes since v6:
> > - Rebased to 4.20
> > - Changelog updated.
> > - No improvement seen on arm64, hence removed removal of prefetch.
> >
> > Changes since v5:
> > - Rebased to 4.20-rc1.
> > - Changelog updated.
> >
> > Changes since v4:
> > - As suggested by Michal Hocko,
> > - Simplify logic in online_pages_block() by using get_order().
> > - Seperate out removal of prefetch from __free_pages_core().
> >
> > Changes since v3:
> > - Renamed _free_pages_boot_core -> __free_pages_core.
> > - Removed prefetch from __free_pages_core.
> > - Removed xen_online_page().
> >
> > Changes since v2:
> > - Reuse code from __free_pages_boot_core().
> >
> > Changes since v1:
> > - Removed prefetch().
> >
> > Changes since RFC:
> > - Rebase.
> > - As suggested by Michal Hocko remove pages_per_block.
> > - Modifed external providers of online_page_callback.
> >
> > v7: https://lore.kernel.org/patchwork/patch/1028908/
> > v6: https://lore.kernel.org/patchwork/patch/1007253/
> > v5: https://lore.kernel.org/patchwork/patch/995739/
> > v4: https://lore.kernel.org/patchwork/patch/995111/
> > v3: https://lore.kernel.org/patchwork/patch/992348/
> > v2: https://lore.kernel.org/patchwork/patch/991363/
> > v1: https://lore.kernel.org/patchwork/patch/989445/
> > RFC: https://lore.kernel.org/patchwork/patch/984754/
> > ---
> >  drivers/hv/hv_balloon.c        |  6 +++--
> >  drivers/xen/balloon.c          | 21 +++++++++++------
> >  include/linux/memory_hotplug.h |  2 +-
> >  mm/internal.h                  |  1 +
> >  mm/memory_hotplug.c            | 51 
> > +++++++++++++++++++++++++++++++-----------
> >  mm/page_alloc.c                |  8 +++----
> >  6 files changed, 62 insertions(+), 27 deletions(-)
> >
> > diff --git a/drivers/hv/hv_balloon.c b/drivers/hv/hv_balloon.c
> > index 5301fef..211f3fe 100644
> > --- a/drivers/hv/hv_balloon.c
> > +++ b/drivers/hv/hv_balloon.c
> > @@ -771,7 +771,7 @@ static void hv_mem_hot_add(unsigned long start, 
> > unsigned long size,
> >  	}
> >  }
> >
> > -static void hv_online_page(struct page *pg)
> > +static int hv_online_page(struct page *pg, unsigned int order)
> >  {
> >  	struct hv_hotadd_state *has;
> >  	unsigned long flags;
> > @@ -783,10 +783,12 @@ static void hv_online_page(struct page *pg)
> >  		if ((pfn < has->start_pfn) || (pfn >= has->end_pfn))
> >  			continue;
> >
> > -		hv_page_online_one(has, pg);
> > +		hv_bring_pgs_online(has, pfn, (1UL << order));
> >  		break;
> >  	}
> >  	spin_unlock_irqrestore(&dm_device.ha_lock, flags);
> > +
> > +	return 0;
> >  }
>
> I would hold off on adding return values until you actually have code
> that uses them. It will make things easier if somebody has to backport
> this to a stable branch and avoid adding complexity until it is needed.
>
> Also the patch description doesn't really explain that it is doing this
> so it might be better to break it off into a separate patch so you can
> call out exactly why you are adding a return value in the patch
> description.
>
> - Alex