From: Peter Zijlstra <peterz@infradead.org>
To: Dave Chinner <david@fromorbit.com>
Cc: Waiman Long <longman@redhat.com>, Ingo Molnar <mingo@redhat.com>,
Will Deacon <will.deacon@arm.com>,
Alexander Viro <viro@zeniv.linux.org.uk>,
Mike Kravetz <mike.kravetz@oracle.com>,
linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
linux-mm@kvack.org, Davidlohr Bueso <dave@stgolabs.net>
Subject: Re: [PATCH 0/5] hugetlbfs: Disable PMD sharing for large systems
Date: Wed, 25 Sep 2019 10:35:57 +0200 [thread overview]
Message-ID: <20190925083557.GA4553@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20190913015043.GF27547@dread.disaster.area>
On Fri, Sep 13, 2019 at 11:50:43AM +1000, Dave Chinner wrote:
> On Wed, Sep 11, 2019 at 04:05:32PM +0100, Waiman Long wrote:
> > A customer with large SMP systems (up to 16 sockets) with application
> > that uses large amount of static hugepages (~500-1500GB) are experiencing
> > random multisecond delays. These delays was caused by the long time it
> > took to scan the VMA interval tree with mmap_sem held.
> >
> > To fix this problem while perserving existing behavior as much as
> > possible, we need to allow timeout in down_write() and disabling PMD
> > sharing when it is taking too long to do so. Since a transaction can
> > involving touching multiple huge pages, timing out for each of the huge
> > page interactions does not completely solve the problem. So a threshold
> > is set to completely disable PMD sharing if too many timeouts happen.
> >
> > The first 4 patches of this 5-patch series adds a new
> > down_write_timedlock() API which accepts a timeout argument and return
> > true is locking is successful or false otherwise. It works more or less
> > than a down_write_trylock() but the calling thread may sleep.
>
> Just on general principle, this is a non-starter. If a lock is being
> held too long, then whatever the lock is protecting needs fixing.
> Adding timeouts to locks and sysctls to tune them is not a viable
> solution to address latencies caused by algorithm scalability
> issues.
I'm very much agreeing here. Lock functions with timeouts are a sign of
horrific design.
prev parent reply other threads:[~2019-09-25 8:36 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-11 15:05 [PATCH 0/5] hugetlbfs: Disable PMD sharing for large systems Waiman Long
2019-09-11 15:05 ` [PATCH 1/5] locking/rwsem: Add down_write_timedlock() Waiman Long
2019-09-11 15:05 ` [PATCH 2/5] locking/rwsem: Enable timeout check when spinning on owner Waiman Long
2019-09-11 15:05 ` [PATCH 3/5] locking/osq: Allow early break from OSQ Waiman Long
2019-09-11 15:05 ` [PATCH 4/5] locking/rwsem: Enable timeout check when staying in the OSQ Waiman Long
2019-09-11 15:05 ` [PATCH 5/5] hugetlbfs: Limit wait time when trying to share huge PMD Waiman Long
2019-09-11 15:14 ` Matthew Wilcox
2019-09-11 15:44 ` Waiman Long
2019-09-11 17:03 ` Mike Kravetz
2019-09-11 17:15 ` Waiman Long
2019-09-11 17:22 ` Qian Cai
2019-09-11 17:28 ` Waiman Long
2019-09-11 16:01 ` Qian Cai
2019-09-11 16:34 ` Waiman Long
2019-09-11 19:42 ` Qian Cai
2019-09-11 20:54 ` Waiman Long
2019-09-11 21:57 ` Qian Cai
2019-09-11 19:57 ` Matthew Wilcox
2019-09-11 20:51 ` Waiman Long
2019-09-12 3:26 ` Mike Kravetz
2019-09-12 3:41 ` Matthew Wilcox
2019-09-12 4:40 ` Davidlohr Bueso
2019-09-16 13:53 ` Waiman Long
2019-09-12 9:06 ` Waiman Long
2019-09-12 16:43 ` Mike Kravetz
2019-09-13 18:23 ` Waiman Long
2019-09-13 1:50 ` [PATCH 0/5] hugetlbfs: Disable PMD sharing for large systems Dave Chinner
2019-09-25 8:35 ` Peter Zijlstra [this message]
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