Linux-Fsdevel Archive on lore.kernel.org
 help / color / Atom feed
From: Dave Chinner <david@fromorbit.com>
To: Waiman Long <longman@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
	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: Fri, 13 Sep 2019 11:50:43 +1000
Message-ID: <20190913015043.GF27547@dread.disaster.area> (raw)
In-Reply-To: <20190911150537.19527-1-longman@redhat.com>

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.

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com

  parent reply index

Thread overview: 28+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-09-11 15:05 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 ` Dave Chinner [this message]
2019-09-25  8:35   ` [PATCH 0/5] hugetlbfs: Disable PMD sharing for large systems Peter Zijlstra

Reply instructions:

You may reply publically to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20190913015043.GF27547@dread.disaster.area \
    --to=david@fromorbit.com \
    --cc=dave@stgolabs.net \
    --cc=linux-fsdevel@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-mm@kvack.org \
    --cc=longman@redhat.com \
    --cc=mike.kravetz@oracle.com \
    --cc=mingo@redhat.com \
    --cc=peterz@infradead.org \
    --cc=viro@zeniv.linux.org.uk \
    --cc=will.deacon@arm.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Linux-Fsdevel Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-fsdevel/0 linux-fsdevel/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-fsdevel linux-fsdevel/ https://lore.kernel.org/linux-fsdevel \
		linux-fsdevel@vger.kernel.org
	public-inbox-index linux-fsdevel

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-fsdevel


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git