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Message-ID: <ZbQW3PRAIw8e7m0m@casper.infradead.org>
Date: Fri, 26 Jan 2024 20:32:28 +0000
From: Matthew Wilcox <willy@...radead.org>
To: Luis Chamberlain <mcgrof@...nel.org>
Cc: kernel test robot <oliver.sang@...el.com>,
Daniel Gomez <da.gomez@...sung.com>, oe-lkp@...ts.linux.dev,
lkp@...el.com, linux-kernel@...r.kernel.org,
"gost.dev@...sung.com" <gost.dev@...sung.com>,
Pankaj Raghav <p.raghav@...sung.com>
Subject: Re: [PATCH 1/2] test_xarray: add tests for advanced multi-index use
On Fri, Jan 26, 2024 at 12:04:44PM -0800, Luis Chamberlain wrote:
> > We have a perfectly good system for "relaxing":
> >
> > xas_for_each_marked(&xas, page, end, PAGECACHE_TAG_DIRTY) {
> > xas_set_mark(&xas, PAGECACHE_TAG_TOWRITE);
> > if (++tagged % XA_CHECK_SCHED)
> > continue;
> >
> > xas_pause(&xas);
> > xas_unlock_irq(&xas);
> > cond_resched();
> > xas_lock_irq(&xas);
> > }
>
> And yet we can get a soft lockup with order 20 (1,048,576 entries),
> granted busy looping over 1 million entries is insane, but it seems it
> the existing code may not be enough to avoid the soft lockup. Also
> cond_resched() may be eventually removed [0].
what? you're in charge of when you sleep. you can do this:
unsigned i = 0;
rcu_read_lock();
xas_for_each(...) {
...
if (iter++ % XA_CHECK_SCHED)
continue;
xas_pause();
rcu_read_unlock();
rcu_read_lock();
}
rcu_read_unlock();
and that will get rid of the rcu warnings. right?
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