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From: Vlastimil Babka <vbabka@suse.cz>
To: Hillf Danton <hillf.zj@alibaba-inc.com>,
	"'Mel Gorman'" <mgorman@techsingularity.net>
Cc: "'Andrew Morton'" <akpm@linux-foundation.org>,
	"'Shantanu Goel'" <sgoel01@yahoo.com>,
	"'Chris Mason'" <clm@fb.com>,
	"'Johannes Weiner'" <hannes@cmpxchg.org>,
	"'LKML'" <linux-kernel@vger.kernel.org>,
	"'Linux-MM'" <linux-mm@kvack.org>
Subject: Re: [PATCH 3/3] mm, vmscan: Prevent kswapd sleeping prematurely due to mismatched classzone_idx
Date: Mon, 20 Feb 2017 17:34:21 +0100	[thread overview]
Message-ID: <d4e3317b-5ae8-f61c-4d71-5a74a4014cc7@suse.cz> (raw)
In-Reply-To: <001f01d2882d$9dd14850$d973d8f0$@alibaba-inc.com>

On 02/16/2017 09:21 AM, Hillf Danton wrote:
> 
> On February 16, 2017 4:11 PM Mel Gorman wrote:
>> On Thu, Feb 16, 2017 at 02:23:08PM +0800, Hillf Danton wrote:
>> > On February 15, 2017 5:23 PM Mel Gorman wrote:
>> > >   */
>> > >  static int kswapd(void *p)
>> > >  {
>> > > -	unsigned int alloc_order, reclaim_order, classzone_idx;
>> > > +	unsigned int alloc_order, reclaim_order;
>> > > +	unsigned int classzone_idx = MAX_NR_ZONES - 1;
>> > >  	pg_data_t *pgdat = (pg_data_t*)p;
>> > >  	struct task_struct *tsk = current;
>> > >
>> > > @@ -3447,20 +3466,23 @@ static int kswapd(void *p)
>> > >  	tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD;
>> > >  	set_freezable();
>> > >
>> > > -	pgdat->kswapd_order = alloc_order = reclaim_order = 0;
>> > > -	pgdat->kswapd_classzone_idx = classzone_idx = 0;
>> > > +	pgdat->kswapd_order = 0;
>> > > +	pgdat->kswapd_classzone_idx = MAX_NR_ZONES;
>> > >  	for ( ; ; ) {
>> > >  		bool ret;
>> > >
>> > > +		alloc_order = reclaim_order = pgdat->kswapd_order;
>> > > +		classzone_idx = kswapd_classzone_idx(pgdat, classzone_idx);
>> > > +
>> > >  kswapd_try_sleep:
>> > >  		kswapd_try_to_sleep(pgdat, alloc_order, reclaim_order,
>> > >  					classzone_idx);
>> > >
>> > >  		/* Read the new order and classzone_idx */
>> > >  		alloc_order = reclaim_order = pgdat->kswapd_order;
>> > > -		classzone_idx = pgdat->kswapd_classzone_idx;
>> > > +		classzone_idx = kswapd_classzone_idx(pgdat, 0);
>> > >  		pgdat->kswapd_order = 0;
>> > > -		pgdat->kswapd_classzone_idx = 0;
>> > > +		pgdat->kswapd_classzone_idx = MAX_NR_ZONES;
>> > >
>> > >  		ret = try_to_freeze();
>> > >  		if (kthread_should_stop())
>> > > @@ -3486,9 +3508,6 @@ static int kswapd(void *p)
>> > >  		reclaim_order = balance_pgdat(pgdat, alloc_order, classzone_idx);
>> > >  		if (reclaim_order < alloc_order)
>> > >  			goto kswapd_try_sleep;
>> >
>> > If we fail order-5 request,  can we then give up order-5, and
>> > try order-3 if requested, after napping?
>> >
>> 
>> That has no bearing upon this patch. At this point, kswapd has stopped
>> reclaiming at the requested order and is preparing to sleep. If there is
>> a parallel request for order-3 while it's sleeping, it'll wake and start
>> reclaiming at order-3 as requested.
>> 
> Right, but the order-3 request can also come up while kswapd is active and
> gives up order-5.

"Giving up on order-5" means it will set sc.order to 0, go to sleep (assuming
order-0 watermarks are OK) and wakeup kcompactd for order-5. There's no way how
kswapd could help an order-3 allocation at that point - it's up to kcompactd.

> thanks
> Hillf
> 

WARNING: multiple messages have this Message-ID (diff)
From: Vlastimil Babka <vbabka@suse.cz>
To: Hillf Danton <hillf.zj@alibaba-inc.com>,
	'Mel Gorman' <mgorman@techsingularity.net>
Cc: 'Andrew Morton' <akpm@linux-foundation.org>,
	'Shantanu Goel' <sgoel01@yahoo.com>, 'Chris Mason' <clm@fb.com>,
	'Johannes Weiner' <hannes@cmpxchg.org>,
	'LKML' <linux-kernel@vger.kernel.org>,
	'Linux-MM' <linux-mm@kvack.org>
Subject: Re: [PATCH 3/3] mm, vmscan: Prevent kswapd sleeping prematurely due to mismatched classzone_idx
Date: Mon, 20 Feb 2017 17:34:21 +0100	[thread overview]
Message-ID: <d4e3317b-5ae8-f61c-4d71-5a74a4014cc7@suse.cz> (raw)
In-Reply-To: <001f01d2882d$9dd14850$d973d8f0$@alibaba-inc.com>

On 02/16/2017 09:21 AM, Hillf Danton wrote:
> 
> On February 16, 2017 4:11 PM Mel Gorman wrote:
>> On Thu, Feb 16, 2017 at 02:23:08PM +0800, Hillf Danton wrote:
>> > On February 15, 2017 5:23 PM Mel Gorman wrote:
>> > >   */
>> > >  static int kswapd(void *p)
>> > >  {
>> > > -	unsigned int alloc_order, reclaim_order, classzone_idx;
>> > > +	unsigned int alloc_order, reclaim_order;
>> > > +	unsigned int classzone_idx = MAX_NR_ZONES - 1;
>> > >  	pg_data_t *pgdat = (pg_data_t*)p;
>> > >  	struct task_struct *tsk = current;
>> > >
>> > > @@ -3447,20 +3466,23 @@ static int kswapd(void *p)
>> > >  	tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD;
>> > >  	set_freezable();
>> > >
>> > > -	pgdat->kswapd_order = alloc_order = reclaim_order = 0;
>> > > -	pgdat->kswapd_classzone_idx = classzone_idx = 0;
>> > > +	pgdat->kswapd_order = 0;
>> > > +	pgdat->kswapd_classzone_idx = MAX_NR_ZONES;
>> > >  	for ( ; ; ) {
>> > >  		bool ret;
>> > >
>> > > +		alloc_order = reclaim_order = pgdat->kswapd_order;
>> > > +		classzone_idx = kswapd_classzone_idx(pgdat, classzone_idx);
>> > > +
>> > >  kswapd_try_sleep:
>> > >  		kswapd_try_to_sleep(pgdat, alloc_order, reclaim_order,
>> > >  					classzone_idx);
>> > >
>> > >  		/* Read the new order and classzone_idx */
>> > >  		alloc_order = reclaim_order = pgdat->kswapd_order;
>> > > -		classzone_idx = pgdat->kswapd_classzone_idx;
>> > > +		classzone_idx = kswapd_classzone_idx(pgdat, 0);
>> > >  		pgdat->kswapd_order = 0;
>> > > -		pgdat->kswapd_classzone_idx = 0;
>> > > +		pgdat->kswapd_classzone_idx = MAX_NR_ZONES;
>> > >
>> > >  		ret = try_to_freeze();
>> > >  		if (kthread_should_stop())
>> > > @@ -3486,9 +3508,6 @@ static int kswapd(void *p)
>> > >  		reclaim_order = balance_pgdat(pgdat, alloc_order, classzone_idx);
>> > >  		if (reclaim_order < alloc_order)
>> > >  			goto kswapd_try_sleep;
>> >
>> > If we fail order-5 request,  can we then give up order-5, and
>> > try order-3 if requested, after napping?
>> >
>> 
>> That has no bearing upon this patch. At this point, kswapd has stopped
>> reclaiming at the requested order and is preparing to sleep. If there is
>> a parallel request for order-3 while it's sleeping, it'll wake and start
>> reclaiming at order-3 as requested.
>> 
> Right, but the order-3 request can also come up while kswapd is active and
> gives up order-5.

"Giving up on order-5" means it will set sc.order to 0, go to sleep (assuming
order-0 watermarks are OK) and wakeup kcompactd for order-5. There's no way how
kswapd could help an order-3 allocation at that point - it's up to kcompactd.

> thanks
> Hillf
> 

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  parent reply	other threads:[~2017-02-20 16:34 UTC|newest]

Thread overview: 50+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-02-15  9:22 [PATCH 0/3] Reduce amount of time kswapd sleeps prematurely Mel Gorman
2017-02-15  9:22 ` Mel Gorman
2017-02-15  9:22 ` [PATCH 1/3] mm, vmscan: fix zone balance check in prepare_kswapd_sleep Mel Gorman
2017-02-15  9:22   ` Mel Gorman
2017-02-16  2:50   ` Hillf Danton
2017-02-16  2:50     ` Hillf Danton
2017-02-22  7:00   ` Minchan Kim
2017-02-22  7:00     ` Minchan Kim
2017-02-23 15:05     ` Mel Gorman
2017-02-23 15:05       ` Mel Gorman
2017-02-24  1:17       ` Minchan Kim
2017-02-24  1:17         ` Minchan Kim
2017-02-24  9:11         ` Mel Gorman
2017-02-24  9:11           ` Mel Gorman
2017-02-27  6:16           ` Minchan Kim
2017-02-27  6:16             ` Minchan Kim
2017-02-15  9:22 ` [PATCH 2/3] mm, vmscan: Only clear pgdat congested/dirty/writeback state when balanced Mel Gorman
2017-02-15  9:22   ` Mel Gorman
2017-02-15  9:22 ` [PATCH 3/3] mm, vmscan: Prevent kswapd sleeping prematurely due to mismatched classzone_idx Mel Gorman
2017-02-15  9:22   ` Mel Gorman
2017-02-16  6:23   ` Hillf Danton
2017-02-16  6:23     ` Hillf Danton
2017-02-16  8:10     ` Mel Gorman
2017-02-16  8:10       ` Mel Gorman
2017-02-16  8:21       ` Hillf Danton
2017-02-16  8:21         ` Hillf Danton
2017-02-16  9:32         ` Mel Gorman
2017-02-16  9:32           ` Mel Gorman
2017-02-20 16:34         ` Vlastimil Babka [this message]
2017-02-20 16:34           ` Vlastimil Babka
2017-02-21  4:10           ` Hillf Danton
2017-02-21  4:10             ` Hillf Danton
2017-02-20 16:42   ` Vlastimil Babka
2017-02-20 16:42     ` Vlastimil Babka
2017-02-23 15:01     ` Mel Gorman
2017-02-23 15:01       ` Mel Gorman
2017-03-01  9:04       ` Vlastimil Babka
2017-03-01  9:04         ` Vlastimil Babka
2017-02-15 20:30 ` [PATCH 0/3] Reduce amount of time kswapd sleeps prematurely Andrew Morton
2017-02-15 20:30   ` Andrew Morton
2017-02-15 21:29   ` Mel Gorman
2017-02-15 21:29     ` Mel Gorman
2017-02-15 21:56     ` Andrew Morton
2017-02-15 21:56       ` Andrew Morton
2017-02-15 22:15       ` Mel Gorman
2017-02-15 22:15         ` Mel Gorman
2017-02-15 22:00     ` Vlastimil Babka
2017-02-15 22:00       ` Vlastimil Babka
2017-03-09  7:56 [PATCH 0/3] Reduce amount of time kswapd sleeps prematurely v2 Mel Gorman
2017-03-09  7:56 ` [PATCH 3/3] mm, vmscan: Prevent kswapd sleeping prematurely due to mismatched classzone_idx Mel Gorman
2017-03-09  7:56   ` Mel Gorman

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