On Thu, Mar 23, 2017 at 02:43:47PM +0100, Jesper Dangaard Brouer wrote:
> On Wed, 22 Mar 2017 23:40:04 +0000
> Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> wrote:
>
> > On Wed, Mar 22, 2017 at 07:39:17PM +0200, Tariq Toukan wrote:
> > > > > > This modification may slow allocations from IRQ context slightly
> > > > > > but the
> > > > > > main gain from the per-cpu allocator is that it scales better for
> > > > > > allocations from multiple contexts. There is an implicit
> > > > > > assumption that
> > > > > > intensive allocations from IRQ contexts on multiple CPUs from a single
> > > > > > NUMA node are rare
> > > Hi Mel, Jesper, and all.
> > >
> > > This assumption contradicts regular multi-stream traffic that is naturally
> > > handled
> > > over close numa cores. I compared iperf TCP multistream (8 streams)
> > > over CX4 (mlx5 driver) with kernels v4.10 (before this series) vs
> > > kernel v4.11-rc1 (with this series).
> > > I disabled the page-cache (recycle) mechanism to stress the page allocator,
> > > and see a drastic degradation in BW, from 47.5 G in v4.10 to 31.4 G in
> > > v4.11-rc1 (34% drop).
> > > I noticed queued_spin_lock_slowpath occupies 62.87% of CPU time.
> >
> > Can you get the stack trace for the spin lock slowpath to confirm it's
> > from IRQ context?
>
> AFAIK allocations happen in softirq. Argh and during review I missed
> that in_interrupt() also covers softirq. To Mel, can we use a in_irq()
> check instead?
>
> (p.s. just landed and got home)
Not built or even boot tested. I'm unable to run tests at the moment
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 6cbde310abed..f82225725bc1 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2481,7 +2481,7 @@ void free_hot_cold_page(struct page *page, bool cold)
unsigned long pfn = page_to_pfn(page);
int migratetype;
- if (in_interrupt()) {
+ if (in_irq()) {
__free_pages_ok(page, 0);
return;
}
@@ -2647,7 +2647,7 @@ static struct page *__rmqueue_pcplist(struct zone *zone, int migratetype,
{
struct page *page;
- VM_BUG_ON(in_interrupt());
+ VM_BUG_ON(in_irq());
do {
if (list_empty(list)) {
@@ -2704,7 +2704,7 @@ struct page *rmqueue(struct zone *preferred_zone,
unsigned long flags;
struct page *page;
- if (likely(order == 0) && !in_interrupt()) {
+ if (likely(order == 0) && !in_irq()) {
page = rmqueue_pcplist(preferred_zone, zone, order,
gfp_flags, migratetype);
goto out;
--
Mel Gorman
SUSE Labs
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