Re: [Xen-devel] [PATCH v3] memory_hotplug: Free pages as higher order

[Arun KS <arunks@xxxxxxxxxxxxxx>]

On 2018-09-27 12:41, Juergen Gross wrote:
> On 27/09/18 08:58, Arun KS wrote:
> > When free pages are done with higher order, time spend 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%.
> >
> > Modify external providers of online callback to align with
> > the change.
> >
> > Signed-off-by: Arun KS <arunks@xxxxxxxxxxxxxx>
> > ---
> > 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.
> >
> > 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          | 18 ++++++++++++++---
> >  include/linux/memory_hotplug.h |  2 +-
> >  mm/internal.h                  |  1 +
> >  mm/memory_hotplug.c            | 44 
> > ++++++++++++++++++++++++++++++------------
> >  mm/page_alloc.c                |  2 +-
> >  6 files changed, 54 insertions(+), 19 deletions(-)
> ...
>
> > diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
> > index e12bb25..010cf4d 100644
> > --- a/drivers/xen/balloon.c
> > +++ b/drivers/xen/balloon.c
> > @@ -390,8 +390,8 @@ static enum bp_state 
> > reserve_additional_memory(void)
> >         /*
> >          * add_memory_resource() will call online_pages() which in its turn
> > -        * will call xen_online_page() callback causing deadlock if we don't
> > -        * release balloon_mutex here. Unlocking here is safe because the
> > +        * will call xen_bring_pgs_online() callback causing deadlock if we
> > +	 * don't release balloon_mutex here. Unlocking here is safe because 
> > the
> >          * callers drop the mutex before trying again.
> >          */
> >         mutex_unlock(&balloon_mutex);
> > @@ -422,6 +422,18 @@ static void xen_online_page(struct page *page)
> >         mutex_unlock(&balloon_mutex);
> >  }
> >
> > +static int xen_bring_pgs_online(struct page *pg, unsigned int order)
> > +{
> > +       unsigned long i, size = (1 << order);
> > +       unsigned long start_pfn = page_to_pfn(pg);
> > +
> > +	pr_debug("Online %lu pages starting at pfn 0x%lx\n", size, 
> > start_pfn);
> > +       for (i = 0; i < size; i++)
> > +               xen_online_page(pfn_to_page(start_pfn + i));
Hi,

> xen_online_page() isn't very complex and this is the only user.
>
> Why don't you move its body in here and drop the extra function?
> And now you can execute the loop with balloon_mutex held instead of
> taking and releasing it in each iteration of the loop.
Point taken. Will incorporate them.

Regards,
Arun
> Juergen
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