Re: [PATCH] mm: vmscan: handle isolated pages with lru lock released
From: Hillf Danton
Date: Sat Jan 14 2012 - 07:05:42 EST
On Fri, Jan 13, 2012 at 11:00 PM, Hillf Danton <dhillf@xxxxxxxxx> wrote:
> When shrinking inactive lru list, isolated pages are queued on locally private
> list, which opens a window for pulling update_isolated_counts() out of the lock
> protection to reduce the lock-hold time.
>
> To achive that, firstly we have to delay updating reclaim stat, which is pointed
> out by Hugh, but not over the deadline where fresh data is used for setting up
> scan budget for shrinking zone in get_scan_count(). The delay is terminated in
> the putback stage after reacquiring lru lock.
>
> Secondly operations related to vm and zone stats, namely __count_vm_events() and
> __mod_zone_page_state(), are proteced with preemption disabled as they
> are per-cpu
> operations.
>
> Thanks for comments and ideas recieved.
>
>
> Signed-off-by: Hillf Danton <dhillf@xxxxxxxxx>
> ---
>
> --- a/mm/vmscan.c    Fri Jan 13 21:30:58 2012
> +++ b/mm/vmscan.c    Fri Jan 13 22:07:14 2012
> @@ -1408,6 +1408,13 @@ putback_lru_pages(struct mem_cgroup_zone
> Â Â Â Â * Put back any unfreeable pages.
> Â Â Â Â */
> Â Â Â Âspin_lock(&zone->lru_lock);
> + Â Â Â /*
> + Â Â Â Â* Here we finish updating reclaim stat that is delayed in
> + Â Â Â Â* update_isolated_counts()
> + Â Â Â Â*/
> + Â Â Â reclaim_stat->recent_scanned[0] += nr_anon;
> + Â Â Â reclaim_stat->recent_scanned[1] += nr_file;
> +
> Â Â Â Âwhile (!list_empty(page_list)) {
> Â Â Â Â Â Â Â Âint lru;
> Â Â Â Â Â Â Â Âpage = lru_to_page(page_list);
> @@ -1461,9 +1468,19 @@ update_isolated_counts(struct mem_cgroup
> Â Â Â Âunsigned long nr_active;
> Â Â Â Âstruct zone *zone = mz->zone;
> Â Â Â Âunsigned int count[NR_LRU_LISTS] = { 0, };
> - Â Â Â struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(mz);
>
> Â Â Â Ânr_active = clear_active_flags(isolated_list, count);
> + Â Â Â /*
> + Â Â Â Â* Without lru lock held,
> + Â Â Â Â* 1, we have to delay updating zone reclaim stat, and the deadline is
> + Â Â Â Â* Â Âwhen fresh data is used for setting up scan budget for another
> + Â Â Â Â* Â Âround shrinking, see get_scan_count(). It is actually updated in
> + Â Â Â Â* Â Âthe putback stage after reacquiring the lock.
> + Â Â Â Â*
> + Â Â Â Â* 2, __count_vm_events() and __mod_zone_page_state() are protected
> + Â Â Â Â* Â Âwith preempt disabled as they are per-cpu operations.
> + Â Â Â Â*/
> + Â Â Â preempt_disable();
> Â Â Â Â__count_vm_events(PGDEACTIVATE, nr_active);
>
> Â Â Â Â__mod_zone_page_state(zone, NR_ACTIVE_FILE,
> @@ -1479,9 +1496,7 @@ update_isolated_counts(struct mem_cgroup
> Â Â Â Â*nr_file = count[LRU_ACTIVE_FILE] + count[LRU_INACTIVE_FILE];
> Â Â Â Â__mod_zone_page_state(zone, NR_ISOLATED_ANON, *nr_anon);
> Â Â Â Â__mod_zone_page_state(zone, NR_ISOLATED_FILE, *nr_file);
> -
> - Â Â Â reclaim_stat->recent_scanned[0] += *nr_anon;
> - Â Â Â reclaim_stat->recent_scanned[1] += *nr_file;
> + Â Â Â preempt_enable();
> Â}
>
> Â/*
> @@ -1577,15 +1592,12 @@ shrink_inactive_list(unsigned long nr_to
> Â Â Â Â Â Â Â Â Â Â Â Â__count_zone_vm_events(PGSCAN_DIRECT, zone,
> Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â nr_scanned);
> Â Â Â Â}
> + Â Â Â spin_unlock_irq(&zone->lru_lock);
>
> - Â Â Â if (nr_taken == 0) {
> - Â Â Â Â Â Â Â spin_unlock_irq(&zone->lru_lock);
> + Â Â Â if (nr_taken == 0)
> Â Â Â Â Â Â Â Âreturn 0;
> - Â Â Â }
>
> Â Â Â Âupdate_isolated_counts(mz, sc, &nr_anon, &nr_file, &page_list);
> -
> - Â Â Â spin_unlock_irq(&zone->lru_lock);
>
> Â Â Â Ânr_reclaimed = shrink_page_list(&page_list, mz, sc, priority,
> Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â&nr_dirty, &nr_writeback);
Hi all
It is re-prepared based on the mainline for easy review.
Thanks
Hillf
===cut here===
From: Hillf Danton <dhillf@xxxxxxxxx>
Subject: [PATCH] mm: vmscan: handle isolated pages with lru lock released
When shrinking inactive lru list, isolated pages are queued on locally private
list, so the lock-hold time could be reduced if pages are counted without lock
protection. To achive that, firstly updating reclaim stat is delayed until the
putback stage, which is pointed out by Hugh, after reacquiring the lru lock.
Secondly operations related to vm and zone stats, are now proteced with
preemption disabled as they are per-cpu operation.
Thanks for comments and ideas received.
Signed-off-by: Hillf Danton <dhillf@xxxxxxxxx>
---
--- a/mm/vmscan.c Sat Jan 14 14:02:20 2012
+++ b/mm/vmscan.c Sat Jan 14 20:00:46 2012
@@ -1414,7 +1414,6 @@ update_isolated_counts(struct mem_cgroup
unsigned long *nr_anon,
unsigned long *nr_file)
{
- struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(mz);
struct zone *zone = mz->zone;
unsigned int count[NR_LRU_LISTS] = { 0, };
unsigned long nr_active = 0;
@@ -1435,6 +1434,7 @@ update_isolated_counts(struct mem_cgroup
count[lru] += numpages;
}
+ preempt_disable();
__count_vm_events(PGDEACTIVATE, nr_active);
__mod_zone_page_state(zone, NR_ACTIVE_FILE,
@@ -1449,8 +1449,9 @@ update_isolated_counts(struct mem_cgroup
*nr_anon = count[LRU_ACTIVE_ANON] + count[LRU_INACTIVE_ANON];
*nr_file = count[LRU_ACTIVE_FILE] + count[LRU_INACTIVE_FILE];
- reclaim_stat->recent_scanned[0] += *nr_anon;
- reclaim_stat->recent_scanned[1] += *nr_file;
+ __mod_zone_page_state(zone, NR_ISOLATED_ANON, *nr_anon);
+ __mod_zone_page_state(zone, NR_ISOLATED_FILE, *nr_file);
+ preempt_enable();
}
/*
@@ -1512,6 +1513,7 @@ shrink_inactive_list(unsigned long nr_to
unsigned long nr_writeback = 0;
isolate_mode_t reclaim_mode = ISOLATE_INACTIVE;
struct zone *zone = mz->zone;
+ struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(mz);
while (unlikely(too_many_isolated(zone, file, sc))) {
congestion_wait(BLK_RW_ASYNC, HZ/10);
@@ -1546,19 +1548,13 @@ shrink_inactive_list(unsigned long nr_to
__count_zone_vm_events(PGSCAN_DIRECT, zone,
nr_scanned);
}
+ spin_unlock_irq(&zone->lru_lock);
- if (nr_taken == 0) {
- spin_unlock_irq(&zone->lru_lock);
+ if (nr_taken == 0)
return 0;
- }
update_isolated_counts(mz, &page_list, &nr_anon, &nr_file);
- __mod_zone_page_state(zone, NR_ISOLATED_ANON, nr_anon);
- __mod_zone_page_state(zone, NR_ISOLATED_FILE, nr_file);
-
- spin_unlock_irq(&zone->lru_lock);
-
nr_reclaimed = shrink_page_list(&page_list, mz, sc, priority,
&nr_dirty, &nr_writeback);
@@ -1570,6 +1566,9 @@ shrink_inactive_list(unsigned long nr_to
}
spin_lock_irq(&zone->lru_lock);
+
+ reclaim_stat->recent_scanned[0] += nr_anon;
+ reclaim_stat->recent_scanned[1] += nr_file;
if (current_is_kswapd())
__count_vm_events(KSWAPD_STEAL, nr_reclaimed);
--
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