From: Michal Hocko <mhocko@kernel.org>
To: Waiman Long <longman@redhat.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>,
Jonathan Corbet <corbet@lwn.net>,
"Luis R. Rodriguez" <mcgrof@kernel.org>,
Kees Cook <keescook@chromium.org>,
linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
linux-mm@kvack.org, linux-doc@vger.kernel.org,
Linus Torvalds <torvalds@linux-foundation.org>,
Jan Kara <jack@suse.cz>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
Andrew Morton <akpm@linux-foundation.org>,
Ingo Molnar <mingo@kernel.org>,
Miklos Szeredi <mszeredi@redhat.com>,
Matthew Wilcox <willy@infradead.org>,
Larry Woodman <lwoodman@redhat.com>,
James Bottomley <James.Bottomley@HansenPartnership.com>,
"Wangkai (Kevin C)" <wangkai86@huawei.com>
Subject: Re: [PATCH v6 0/7] fs/dcache: Track & limit # of negative dentries
Date: Wed, 11 Jul 2018 12:21:39 +0200 [thread overview]
Message-ID: <20180711102139.GG20050@dhcp22.suse.cz> (raw)
In-Reply-To: <a2794bcc-9193-cbca-3a54-47420a2ab52c@redhat.com>
On Tue 10-07-18 12:09:17, Waiman Long wrote:
> On 07/10/2018 10:27 AM, Michal Hocko wrote:
> > On Mon 09-07-18 12:01:04, Waiman Long wrote:
> >> On 07/09/2018 04:19 AM, Michal Hocko wrote:
[...]
> >>> percentage has turned out to be a really wrong unit for many tunables
> >>> over time. Even 1% can be just too much on really large machines.
> >> Yes, that is true. Do you have any suggestion of what kind of unit
> >> should be used? I can scale down the unit to 0.1% of the system memory.
> >> Alternatively, one unit can be 10k/cpu thread, so a 20-thread system
> >> corresponds to 200k, etc.
> > I simply think this is a strange user interface. How much is a
> > reasonable number? How can any admin figure that out?
>
> Without the optional enforcement, the limit is essentially just a
> notification mechanism where the system signals that there is something
> wrong going on and the system administrator need to take a look. So it
> is perfectly OK if the limit is sufficiently high that normally we won't
> need to use that many negative dentries. The goal is to prevent negative
> dentries from consuming a significant portion of the system memory.
So again. How do you tell the right number?
> I am going to reduce the granularity of each unit to 1/1000 of the total
> system memory so that for large system with TB of memory, a smaller
> amount of memory can be specified.
It is just a matter of time for this to be too coarse as well.
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2018-07-11 10:21 UTC|newest]
Thread overview: 49+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-07-06 19:32 [PATCH v6 0/7] fs/dcache: Track & limit # of negative dentries Waiman Long
2018-07-06 19:32 ` [PATCH v6 1/7] fs/dcache: Track & report number " Waiman Long
2018-07-06 19:32 ` [PATCH v6 2/7] fs/dcache: Add sysctl parameter neg-dentry-pc as a soft limit on " Waiman Long
2018-07-06 19:32 ` [PATCH v6 3/7] fs/dcache: Enable automatic pruning of " Waiman Long
2018-07-06 19:32 ` [PATCH v6 4/7] fs/dcache: Spread negative dentry pruning across multiple CPUs Waiman Long
2018-07-06 19:32 ` [PATCH v6 5/7] fs/dcache: Add negative dentries to LRU head initially Waiman Long
2018-07-06 19:32 ` [PATCH v6 6/7] fs/dcache: Allow optional enforcement of negative dentry limit Waiman Long
2018-07-06 19:32 ` [PATCH v6 7/7] fs/dcache: Allow deconfiguration of negative dentry code to reduce kernel size Waiman Long
2018-07-06 21:54 ` Eric Biggers
2018-07-06 22:28 ` [PATCH v6 0/7] fs/dcache: Track & limit # of negative dentries Al Viro
2018-07-07 3:02 ` Waiman Long
2018-07-09 8:19 ` Michal Hocko
2018-07-09 16:01 ` Waiman Long
2018-07-10 14:27 ` Michal Hocko
2018-07-10 16:09 ` Waiman Long
2018-07-11 10:21 ` Michal Hocko [this message]
2018-07-11 15:13 ` Waiman Long
2018-07-11 17:42 ` James Bottomley
2018-07-11 19:07 ` Waiman Long
2018-07-11 19:21 ` James Bottomley
2018-07-12 15:54 ` Waiman Long
2018-07-12 16:04 ` James Bottomley
2018-07-12 16:26 ` Waiman Long
2018-07-12 17:33 ` James Bottomley
2018-07-13 15:32 ` Waiman Long
2018-07-12 16:49 ` Matthew Wilcox
2018-07-12 17:21 ` James Bottomley
2018-07-12 18:06 ` Linus Torvalds
2018-07-12 19:57 ` James Bottomley
2018-07-13 0:36 ` Dave Chinner
2018-07-13 15:46 ` James Bottomley
2018-07-13 23:17 ` Dave Chinner
2018-07-16 9:10 ` Michal Hocko
2018-07-16 14:42 ` James Bottomley
2018-07-16 9:09 ` Michal Hocko
2018-07-16 9:12 ` Michal Hocko
2018-07-16 12:41 ` Matthew Wilcox
2018-07-16 23:40 ` Andrew Morton
2018-07-17 1:30 ` Matthew Wilcox
2018-07-17 8:33 ` Michal Hocko
2018-07-19 0:33 ` Dave Chinner
2018-07-19 8:45 ` Michal Hocko
2018-07-19 9:13 ` Jan Kara
2018-07-18 18:39 ` Waiman Long
2018-07-18 16:17 ` Waiman Long
2018-07-19 8:48 ` Michal Hocko
2018-07-12 8:48 ` Michal Hocko
2018-07-12 16:12 ` Waiman Long
2018-07-12 23:16 ` Andrew Morton
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