Re: [PATCH v9] mm/page_alloc.c: memory_hotplug: free pages as higher order
From: Arun KS
Date: Mon Jan 14 2019 - 11:32:42 EST
On 2019-01-14 21:45, Alexander Duyck wrote:
On Mon, 2019-01-14 at 19:29 +0530, Arun KS wrote:
On 2019-01-10 21:53, Alexander Duyck wrote:
> On Thu, 2019-01-10 at 11:05 +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>
>
> So I decided to give this one last thorough review and I think I might
> have found a few more minor issues, but not anything that is
> necessarily a showstopper.
>
> Reviewed-by: Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx>
>
> > ---
> > Changes since v8:
> > - Remove return type change for online_page_callback.
> > - Use consistent names for external online_page providers.
> > - Fix onlined_pages accounting.
> >
> > 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.
> >
> > 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.
> >
> > v8: https://lore.kernel.org/patchwork/patch/1030332/
> > 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 | 4 ++--
> > drivers/xen/balloon.c | 15 ++++++++++-----
> > include/linux/memory_hotplug.h | 2 +-
> > mm/internal.h | 1 +
> > mm/memory_hotplug.c | 37
> > +++++++++++++++++++++++++------------
> > mm/page_alloc.c | 8 ++++----
> > 6 files changed, 43 insertions(+), 24 deletions(-)
> >
> > diff --git a/drivers/hv/hv_balloon.c b/drivers/hv/hv_balloon.c
> > index 5301fef..55d79f8 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 void hv_online_page(struct page *pg, unsigned int order)
> > {
> > struct hv_hotadd_state *has;
> > unsigned long flags;
> > @@ -783,7 +783,7 @@ static void hv_online_page(struct page *pg)
> > if ((pfn < has->start_pfn) || (pfn >= has->end_pfn))
> > continue;
> >
>
> I haven't followed earlier reviews, but do we know for certain the
> entire range being onlined will fit within a single hv_hotadd_state? If
> nothing else it seems like this check should be updated so that we are
> checking to verify that pfn + (1UL << order) is less than or equal to
> has->end_pfn.
Good catch. I ll change the check to,
if ((pfn < has->start_pfn) ||
(pfn + (1UL << order) >= 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);
> > diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
> > index ceb5048..d107447 100644
> > --- a/drivers/xen/balloon.c
> > +++ b/drivers/xen/balloon.c
> > @@ -369,14 +369,19 @@ static enum bp_state
> > reserve_additional_memory(void)
> > return BP_ECANCELED;
> > }
> >
> > -static void xen_online_page(struct page *page)
> > +static void xen_online_page(struct page *page, unsigned int order)
> > {
> > - __online_page_set_limits(page);
> > + unsigned long i, size = (1 << order);
> > + unsigned long start_pfn = page_to_pfn(page);
> > + struct page *p;
> >
> > + pr_debug("Online %lu pages starting at pfn 0x%lx\n", size,
> > start_pfn);
> > mutex_lock(&balloon_mutex);
> > -
> > - __balloon_append(page);
> > -
> > + for (i = 0; i < size; i++) {
> > + p = pfn_to_page(start_pfn + i);
> > + __online_page_set_limits(p);
> > + __balloon_append(p);
> > + }
> > mutex_unlock(&balloon_mutex);
> > }
> >
> > diff --git a/include/linux/memory_hotplug.h
> > b/include/linux/memory_hotplug.h
> > index 07da5c6..e368730 100644
> > --- a/include/linux/memory_hotplug.h
> > +++ b/include/linux/memory_hotplug.h
> > @@ -87,7 +87,7 @@ extern int test_pages_in_a_zone(unsigned long
> > start_pfn, unsigned long end_pfn,
> > unsigned long *valid_start, unsigned long *valid_end);
> > extern void __offline_isolated_pages(unsigned long, unsigned long);
> >
> > -typedef void (*online_page_callback_t)(struct page *page);
> > +typedef void (*online_page_callback_t)(struct page *page, unsigned
> > int order);
> >
> > extern int set_online_page_callback(online_page_callback_t callback);
> > extern int restore_online_page_callback(online_page_callback_t
> > callback);
> > diff --git a/mm/internal.h b/mm/internal.h
> > index f4a7bb0..536bc2a 100644
> > --- a/mm/internal.h
> > +++ b/mm/internal.h
> > @@ -163,6 +163,7 @@ static inline struct page
> > *pageblock_pfn_to_page(unsigned long start_pfn,
> > extern int __isolate_free_page(struct page *page, unsigned int
> > order);
> > extern void memblock_free_pages(struct page *page, unsigned long pfn,
> > unsigned int order);
> > +extern void __free_pages_core(struct page *page, unsigned int order);
> > extern void prep_compound_page(struct page *page, unsigned int
> > order);
> > extern void post_alloc_hook(struct page *page, unsigned int order,
> > gfp_t gfp_flags);
> > diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> > index b9a667d..77dff24 100644
> > --- a/mm/memory_hotplug.c
> > +++ b/mm/memory_hotplug.c
> > @@ -47,7 +47,7 @@
> > * and restore_online_page_callback() for generic callback restore.
> > */
> >
> > -static void generic_online_page(struct page *page);
> > +static void generic_online_page(struct page *page, unsigned int
> > order);
> >
> > static online_page_callback_t online_page_callback =
> > generic_online_page;
> > static DEFINE_MUTEX(online_page_callback_lock);
> > @@ -656,26 +656,39 @@ void __online_page_free(struct page *page)
> > }
> > EXPORT_SYMBOL_GPL(__online_page_free);
> >
> > -static void generic_online_page(struct page *page)
> > +static void generic_online_page(struct page *page, unsigned int
> > order)
> > {
> > - __online_page_set_limits(page);
> > - __online_page_increment_counters(page);
> > - __online_page_free(page);
> > + __free_pages_core(page, order);
> > + totalram_pages_add(1UL << order);
> > +#ifdef CONFIG_HIGHMEM
> > + if (PageHighMem(page))
> > + totalhigh_pages_add(1UL << order);
> > +#endif
> > +}
> > +
> > +static int online_pages_blocks(unsigned long start, unsigned long
> > nr_pages)
> > +{
> > + unsigned long end = start + nr_pages;
> > + int order, ret, onlined_pages = 0;
> > +
> > + while (start < end) {
> > + order = min(MAX_ORDER - 1,
> > + get_order(PFN_PHYS(end) - PFN_PHYS(start)));
>
> So this is mostly just optimization related so you can ignore this
> suggestion if you want. I was looking at this and it occurred to me
> that I don't think you need to convert this to a physical address do
> you?
>
> Couldn't you just do something like the following:
> if ((end - start) >= (1UL << (MAX_ORDER - 1))
> order = MAX_ORDER - 1;
> else
> order = __fls(end - start);
>
> I would think this would save you a few steps in terms of conversions
> and such since you are already working in page frame numbers anyway so
> a block of 8 pfns would represent an order 3 page wouldn't it?
>
> Also it seems like an alternative to using "end" would be to just track
> nr_pages. Then you wouldn't have to do the "end - start" math in a few
> spots as long as you remembered to decrement nr_pages by the amount you
> increment start by.
Thanks for that. How about this?
static int online_pages_blocks(unsigned long start, unsigned long
nr_pages)
{
unsigned long end = start + nr_pages;
int order;
while (nr_pages) {
if (nr_pages >= (1UL << (MAX_ORDER - 1)))
order = MAX_ORDER - 1;
else
order = __fls(nr_pages);
(*online_page_callback)(pfn_to_page(start), order);
nr_pages -= (1UL << order);
start += (1UL << order);
}
return end - start;
}
Regards,
Arun
You would still need to return onlined_pages or something similar at
the end of the function. The problem is end - start should always be 0
if your loop succeeds. Either that or you could save of nr_pages to
onlined_pages directly and then return that and the end of the
function.
Oh right. Considering Michal's comment, I ll leave this as it is for
now.
Regards,
Arun