On Fri, Jul 23, 2010 at 11:10:49PM +0800, KOSAKI Motohiro wrote:
> > The zone->lru_lock is heavily contented in workload where activate_page()
> > is frequently used. We could do batch activate_page() to reduce the lock
> > contention. The batched pages will be added into zone list when the pool
> > is full or page reclaim is trying to drain them.
> >
> > For example, in a 4 socket 64 CPU system, create a sparse file and 64 processes,
> > processes shared map to the file. Each process read access the whole file and
> > then exit. The process exit will do unmap_vmas() and cause a lot of
> > activate_page() call. In such workload, we saw about 58% total time reduction
> > with below patch.
>
> I'm not sure this. Why process exiting on your workload call unmap_vmas?
> Can you please explain why we can't stop activate_page? Is this proper page activation?
>
>
> >
> > But we did see some strange regression. The regression is small (usually < 2%)
> > and most are from multithread test and none heavily use activate_page(). For
> > example, in the same system, we create 64 threads. Each thread creates a private
> > mmap region and does read access. We measure the total time and saw about 2%
> > regression. But in such workload, 99% time is on page fault and activate_page()
> > takes no time. Very strange, we haven't a good explanation for this so far,
> > hopefully somebody can share a hint.
> >
> > Signed-off-by: Shaohua Li <shaohua.li@xxxxxxxxx>
> >
> > diff --git a/mm/swap.c b/mm/swap.c
> > index 3ce7bc3..4a3fd7f 100644
> > --- a/mm/swap.c
> > +++ b/mm/swap.c
> > @@ -39,6 +39,7 @@ int page_cluster;
> >
> > static DEFINE_PER_CPU(struct pagevec[NR_LRU_LISTS], lru_add_pvecs);
> > static DEFINE_PER_CPU(struct pagevec, lru_rotate_pvecs);
> > +static DEFINE_PER_CPU(struct pagevec, activate_page_pvecs);
> >
> > /*
> > * This path almost never happens for VM activity - pages are normally
> > @@ -175,11 +176,10 @@ static void update_page_reclaim_stat(struct zone *zone, struct page *page,
> > /*
> > * FIXME: speed this up?
> > */
> > -void activate_page(struct page *page)
> > +static void __activate_page(struct page *page)
> > {
> > struct zone *zone = page_zone(page);
>
> this page_zone() can move in following branch.
>
>
> > - spin_lock_irq(&zone->lru_lock);
> > if (PageLRU(page) && !PageActive(page) && !PageUnevictable(page)) {
> > int file = page_is_file_cache(page);
> > int lru = page_lru_base_type(page);
> > @@ -192,7 +192,46 @@ void activate_page(struct page *page)
> >
> > update_page_reclaim_stat(zone, page, file, 1);
> > }
> > - spin_unlock_irq(&zone->lru_lock);
> > +}
> > +
> > +static void activate_page_drain_cpu(int cpu)
> > +{
> > + struct pagevec *pvec = &per_cpu(activate_page_pvecs, cpu);
> > + struct zone *last_zone = NULL, *zone;
> > + int i, j;
> > +
> > + for (i = 0; i < pagevec_count(pvec); i++) {
> > + zone = page_zone(pvec->pages[i]);
> > + if (zone == last_zone)
> > + continue;
> > +
> > + if (last_zone)
> > + spin_unlock_irq(&last_zone->lru_lock);
> > + last_zone = zone;
> > + spin_lock_irq(&last_zone->lru_lock);
> > +
> > + for (j = i; j < pagevec_count(pvec); j++) {
> > + struct page *page = pvec->pages[j];
> > +
> > + if (last_zone != page_zone(page))
> > + continue;
> > + __activate_page(page);
> > + }
> > + }
> > + if (last_zone)
> > + spin_unlock_irq(&last_zone->lru_lock);
> > + release_pages(pvec->pages, pagevec_count(pvec), pvec->cold);
> > + pagevec_reinit(pvec);
> > +}
>
> Can we unify this and ____pagevec_lru_add(). they are very similar.
Very good suggestions. I slightly updated the patch to reduce some locking
in worst case in pagevec_lru_move_fn(). Since the regression I mentioned
before isn't stable, I removed that comment too. Below is updated patch.
Thanks,
Shaohua
Subject: mm: batch activate_page() to reduce lock contention
The zone->lru_lock is heavily contented in workload where activate_page()
is frequently used. We could do batch activate_page() to reduce the lock
contention. The batched pages will be added into zone list when the pool
is full or page reclaim is trying to drain them.
For example, in a 4 socket 64 CPU system, create a sparse file and 64 processes,
processes shared map to the file. Each process read access the whole file and
then exit. The process exit will do unmap_vmas() and cause a lot of
activate_page() call. In such workload, we saw about 58% total time reduction
with below patch.
Signed-off-by: Shaohua Li <shaohua.li@xxxxxxxxx>
Reviewed-by: Minchan Kim <minchan.kim@xxxxxxxxx>
Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
diff --git a/mm/swap.c b/mm/swap.c
index 3ce7bc3..3738134 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -39,6 +39,7 @@ int page_cluster;
static DEFINE_PER_CPU(struct pagevec[NR_LRU_LISTS], lru_add_pvecs);
static DEFINE_PER_CPU(struct pagevec, lru_rotate_pvecs);
+static DEFINE_PER_CPU(struct pagevec, activate_page_pvecs);
/*
* This path almost never happens for VM activity - pages are normally
@@ -172,27 +173,72 @@ static void update_page_reclaim_stat(struct zone *zone, struct page *page,
memcg_reclaim_stat->recent_rotated[file]++;
}
-/*
- * FIXME: speed this up?
- */
-void activate_page(struct page *page)
+static void __activate_page(struct page *page, void *arg)
{
- struct zone *zone = page_zone(page);
-
- spin_lock_irq(&zone->lru_lock);
if (PageLRU(page) && !PageActive(page) && !PageUnevictable(page)) {
+ struct zone *zone = page_zone(page);
int file = page_is_file_cache(page);
int lru = page_lru_base_type(page);
+
del_page_from_lru_list(zone, page, lru);
SetPageActive(page);
lru += LRU_ACTIVE;
add_page_to_lru_list(zone, page, lru);
- __count_vm_event(PGACTIVATE);
+ __count_vm_event(PGACTIVATE);
update_page_reclaim_stat(zone, page, file, 1);
}
- spin_unlock_irq(&zone->lru_lock);
+}
+
+static void pagevec_lru_move_fn(struct pagevec *pvec,
+ void (*move_fn)(struct page *page, void *arg),
+ void *arg)
+{
+ struct zone *last_zone = NULL;
+ int i, j;
+ DECLARE_BITMAP(pages_done, PAGEVEC_SIZE);
+
+ bitmap_zero(pages_done, PAGEVEC_SIZE);
+ for (i = 0; i < pagevec_count(pvec); i++) {
+ if (test_bit(i, pages_done))
+ continue;
+
+ if (last_zone)
+ spin_unlock_irq(&last_zone->lru_lock);
+ last_zone = page_zone(pvec->pages[i]);
+ spin_lock_irq(&last_zone->lru_lock);
+
+ for (j = i; j < pagevec_count(pvec); j++) {
+ struct page *page = pvec->pages[j];
+
+ if (last_zone != page_zone(page))
+ continue;
+ (*move_fn)(page, arg);
+ __set_bit(j, pages_done);
+ }
+ }
+ if (last_zone)
+ spin_unlock_irq(&last_zone->lru_lock);
+ release_pages(pvec->pages, pagevec_count(pvec), pvec->cold);
+ pagevec_reinit(pvec);
+}
+
+static void activate_page_drain(struct pagevec *pvec)
+{
+ pagevec_lru_move_fn(pvec, __activate_page, NULL);
+}
+
+void activate_page(struct page *page)
+{
+ if (PageLRU(page) && !PageActive(page) && !PageUnevictable(page)) {
+ struct pagevec *pvec = &get_cpu_var(activate_page_pvecs);
+
+ page_cache_get(page);
+ if (!pagevec_add(pvec, page))
+ activate_page_drain(pvec);
+ put_cpu_var(activate_page_pvecs);
+ }
}
/*
@@ -292,6 +338,10 @@ static void drain_cpu_pagevecs(int cpu)
pagevec_move_tail(pvec);
local_irq_restore(flags);
}
+
+ pvec = &per_cpu(activate_page_pvecs, cpu);
+ if (pagevec_count(pvec))
+ activate_page_drain(pvec);
}
void lru_add_drain(void)
@@ -398,46 +448,34 @@ void __pagevec_release(struct pagevec *pvec)
EXPORT_SYMBOL(__pagevec_release);
+static void ____pagevec_lru_add_fn(struct page *page, void *arg)
+{
+ enum lru_list lru = (enum lru_list)arg;
+ struct zone *zone = page_zone(page);
+ int file = is_file_lru(lru);
+ int active = is_active_lru(lru);
+
+ VM_BUG_ON(PageActive(page));
+ VM_BUG_ON(PageUnevictable(page));
+ VM_BUG_ON(PageLRU(page));
+
+ SetPageLRU(page);
+ if (active)
+ SetPageActive(page);
+ update_page_reclaim_stat(zone, page, file, active);
+ add_page_to_lru_list(zone, page, lru);
+}
+
/*
* Add the passed pages to the LRU, then drop the caller's refcount
* on them. Reinitialises the caller's pagevec.
*/
void ____pagevec_lru_add(struct pagevec *pvec, enum lru_list lru)
{
- int i;
- struct zone *zone = NULL;
-
VM_BUG_ON(is_unevictable_lru(lru));
- for (i = 0; i < pagevec_count(pvec); i++) {
- struct page *page = pvec->pages[i];
- struct zone *pagezone = page_zone(page);
- int file;
- int active;
-
- if (pagezone != zone) {
- if (zone)
- spin_unlock_irq(&zone->lru_lock);
- zone = pagezone;
- spin_lock_irq(&zone->lru_lock);
- }
- VM_BUG_ON(PageActive(page));
- VM_BUG_ON(PageUnevictable(page));
- VM_BUG_ON(PageLRU(page));
- SetPageLRU(page);
- active = is_active_lru(lru);
- file = is_file_lru(lru);
- if (active)
- SetPageActive(page);
- update_page_reclaim_stat(zone, page, file, active);
- add_page_to_lru_list(zone, page, lru);
- }
- if (zone)
- spin_unlock_irq(&zone->lru_lock);
- release_pages(pvec->pages, pvec->nr, pvec->cold);
- pagevec_reinit(pvec);
+ pagevec_lru_move_fn(pvec, ____pagevec_lru_add_fn, (void *)lru);
}
-
EXPORT_SYMBOL(____pagevec_lru_add);
/*
--
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