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From: Mel Gorman <mgorman@techsingularity.net>
To: Dave Chinner <david@fromorbit.com>
Cc: NeilBrown <neilb@suse.de>, Linux-MM <linux-mm@kvack.org>,
	Theodore Ts'o <tytso@mit.edu>,
	Andreas Dilger <adilger.kernel@dilger.ca>,
	"Darrick J . Wong" <djwong@kernel.org>,
	Matthew Wilcox <willy@infradead.org>,
	Michal Hocko <mhocko@suse.com>, Rik van Riel <riel@surriel.com>,
	Vlastimil Babka <vbabka@suse.cz>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Jonathan Corbet <corbet@lwn.net>,
	Linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 1/5] mm/vmscan: Throttle reclaim until some writeback completes if congested
Date: Wed, 22 Sep 2021 09:03:51 +0100	[thread overview]
Message-ID: <20210922080351.GU3959@techsingularity.net> (raw)
In-Reply-To: <20210922060447.GA2361455@dread.disaster.area>

On Wed, Sep 22, 2021 at 04:04:47PM +1000, Dave Chinner wrote:
> On Tue, Sep 21, 2021 at 11:58:31AM +0100, Mel Gorman wrote:
> > On Tue, Sep 21, 2021 at 10:13:17AM +1000, NeilBrown wrote:
> > > On Mon, 20 Sep 2021, Mel Gorman wrote:
> > > > -long wait_iff_congested(int sync, long timeout)
> > > > -{
> > > > -	long ret;
> > > > -	unsigned long start = jiffies;
> > > > -	DEFINE_WAIT(wait);
> > > > -	wait_queue_head_t *wqh = &congestion_wqh[sync];
> > > > -
> > > > -	/*
> > > > -	 * If there is no congestion, yield if necessary instead
> > > > -	 * of sleeping on the congestion queue
> > > > -	 */
> > > > -	if (atomic_read(&nr_wb_congested[sync]) == 0) {
> > > > -		cond_resched();
> > > > -
> > > > -		/* In case we scheduled, work out time remaining */
> > > > -		ret = timeout - (jiffies - start);
> > > > -		if (ret < 0)
> > > > -			ret = 0;
> > > > -
> > > > -		goto out;
> > > > -	}
> > > > -
> > > > -	/* Sleep until uncongested or a write happens */
> > > > -	prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
> > > 
> > > Uninterruptible wait.
> > > 
> > > ....
> > > > +static void
> > > > +reclaim_throttle(pg_data_t *pgdat, enum vmscan_throttle_state reason,
> > > > +							long timeout)
> > > > +{
> > > > +	wait_queue_head_t *wqh = &pgdat->reclaim_wait;
> > > > +	unsigned long start = jiffies;
> > > > +	long ret;
> > > > +	DEFINE_WAIT(wait);
> > > > +
> > > > +	atomic_inc(&pgdat->nr_reclaim_throttled);
> > > > +	WRITE_ONCE(pgdat->nr_reclaim_start,
> > > > +		 node_page_state(pgdat, NR_THROTTLED_WRITTEN));
> > > > +
> > > > +	prepare_to_wait(wqh, &wait, TASK_INTERRUPTIBLE);
> > > 
> > > Interruptible wait.
> > > 
> > > Why the change?  I think these waits really need to be TASK_UNINTERRUPTIBLE.
> > > 
> > 
> > Because from mm/ context, I saw no reason why the task *should* be
> > uninterruptible. It's waiting on other tasks to complete IO and it is not
> > protecting device state, filesystem state or anything else. If it gets
> > a signal, it's safe to wake up, particularly if that signal is KILL and
> > the context is a direct reclaimer.
> 
> I disagree. whether the sleep should be interruptable or
> not is entirely dependent on whether the caller can handle failure
> or not. If this is GFP_NOFAIL, allocation must not fail no matter
> what the context is, so signals and the like are irrelevant.
> 
> For a context that can handle allocation failure, then it makes
> sense to wake on events that will result in the allocation failing
> immediately. But if all this does is make the allocation code go
> around another retry loop sooner, then an interruptible sleep still
> doesn't make any sense at all here...
> 

Ok, between this and Neil's mail on the same topic, I'm convinced.

-- 
Mel Gorman
SUSE Labs

  reply	other threads:[~2021-09-22  8:03 UTC|newest]

Thread overview: 33+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-20  8:54 [RFC PATCH 0/5] Remove dependency on congestion_wait in mm/ Mel Gorman
2021-09-20  8:54 ` [PATCH 1/5] mm/vmscan: Throttle reclaim until some writeback completes if congested Mel Gorman
2021-09-20 23:19   ` NeilBrown
2021-09-21 11:12     ` Mel Gorman
2021-09-21 21:27       ` NeilBrown
2021-09-21  0:13   ` NeilBrown
2021-09-21 10:58     ` Mel Gorman
2021-09-21 21:40       ` NeilBrown
2021-09-22  6:04       ` Dave Chinner
2021-09-22  8:03         ` Mel Gorman [this message]
2021-09-22 12:16   ` Hillf Danton
2021-09-22 14:13     ` Mel Gorman
2021-09-20  8:54 ` [PATCH 2/5] mm/vmscan: Throttle reclaim and compaction when too may pages are isolated Mel Gorman
2021-09-20 23:27   ` NeilBrown
2021-09-21 11:03     ` Mel Gorman
2021-09-21 18:45   ` Yang Shi
2021-09-21 18:45     ` Yang Shi
2021-09-22  8:11     ` Mel Gorman
2021-09-20  8:54 ` [PATCH 3/5] mm/vmscan: Throttle reclaim when no progress is being made Mel Gorman
2021-09-20 23:31   ` NeilBrown
2021-09-21 11:16     ` Mel Gorman
2021-09-21 21:46       ` NeilBrown
2021-09-22  9:21         ` Mel Gorman
2021-09-20  8:54 ` [PATCH 4/5] mm/writeback: Throttle based on page writeback instead of congestion Mel Gorman
2021-09-20  8:54 ` [PATCH 5/5] mm/page_alloc: Remove the throttling logic from the page allocator Mel Gorman
2021-09-20 11:42 ` [RFC PATCH 0/5] Remove dependency on congestion_wait in mm/ Matthew Wilcox
2021-09-20 12:50   ` Mel Gorman
2021-09-20 14:11     ` David Sterba
2021-09-21 11:18       ` Mel Gorman
2021-09-20 19:51   ` Mel Gorman
2021-09-21 20:46 ` Dave Chinner
2021-09-22 17:52   ` Mel Gorman
2021-09-29 10:09 [PATCH 0/5] Remove dependency on congestion_wait in mm/ v2 Mel Gorman
2021-09-29 10:09 ` [PATCH 1/5] mm/vmscan: Throttle reclaim until some writeback completes if congested Mel Gorman

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