From: James Bottomley <James.Bottomley@HansenPartnership.com>
To: Dave Chinner <david@fromorbit.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Matthew Wilcox <willy@infradead.org>,
Waiman Long <longman@redhat.com>,
Michal Hocko <mhocko@kernel.org>,
Al Viro <viro@zeniv.linux.org.uk>,
Jonathan Corbet <corbet@lwn.net>,
"Luis R. Rodriguez" <mcgrof@kernel.org>,
Kees Cook <keescook@chromium.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
linux-mm <linux-mm@kvack.org>,
"open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
Jan Kara <jack@suse.cz>,
Paul McKenney <paulmck@linux.vnet.ibm.com>,
Andrew Morton <akpm@linux-foundation.org>,
Ingo Molnar <mingo@kernel.org>,
Miklos Szeredi <mszeredi@redhat.com>,
Larry Woodman <lwoodman@redhat.com>,
"Wangkai (Kevin,C)" <wangkai86@huawei.com>
Subject: Re: [PATCH v6 0/7] fs/dcache: Track & limit # of negative dentries
Date: Fri, 13 Jul 2018 08:46:52 -0700 [thread overview]
Message-ID: <1531496812.3361.9.camel@HansenPartnership.com> (raw)
In-Reply-To: <20180713003614.GW2234@dastard>
On Fri, 2018-07-13 at 10:36 +1000, Dave Chinner wrote:
> On Thu, Jul 12, 2018 at 12:57:15PM -0700, James Bottomley wrote:
> > What surprises me most about this behaviour is the steadiness of
> > the page cache ... I would have thought we'd have shrunk it
> > somewhat given the intense call on the dcache.
>
> Oh, good, the page cache vs superblock shrinker balancing still
> protects the working set of each cache the way it's supposed to
> under heavy single cache pressure. :)
Well, yes, but my expectation is most of the page cache is clean, so
easily reclaimable. I suppose part of my surprise is that I expected
us to reclaim the clean caches first before we started pushing out the
dirty stuff and reclaiming it. I'm not saying it's a bad thing, just
saying I didn't expect us to make such good decisions under the
parameters of this test.
> Keep in mind that the amount of work slab cache shrinkers perform is
> directly proportional to the amount of page cache reclaim that is
> performed and the size of the slab cache being reclaimed. IOWs,
> under a "single cache pressure" workload we should be directing
> reclaim work to the huge cache creating the pressure and do very
> little reclaim from other caches....
That definitely seems to happen. The thing I was most surprised about
is the steady pushing of anonymous objects to swap. I agree the dentry
cache doesn't seem to be growing hugely after the initial jump, so it
seems to be the largest source of reclaim.
> [ What follows from here is conjecture, but is based on what I've
> seen in the past 10+ years on systems with large numbers of negative
> dentries and fragmented dentry/inode caches. ]
OK, so I fully agree with the concern about pathological object vs page
freeing problems (I referred to it previously). However, I did think
the compaction work that's been ongoing in mm was supposed to help
here?
James
WARNING: multiple messages have this Message-ID (diff)
From: James Bottomley <James.Bottomley@HansenPartnership.com>
To: Dave Chinner <david@fromorbit.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Matthew Wilcox <willy@infradead.org>,
Waiman Long <longman@redhat.com>,
Michal Hocko <mhocko@kernel.org>,
Al Viro <viro@zeniv.linux.org.uk>,
Jonathan Corbet <corbet@lwn.net>,
"Luis R. Rodriguez" <mcgrof@kernel.org>,
Kees Cook <keescook@chromium.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
linux-mm <linux-mm@kvack.org>,
"open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
Jan Kara <jack@suse.cz>,
Paul McKenney <paulmck@linux.vnet.ibm.com>,
Andrew Morton <akpm@linux-foundation.org>,
Ingo Molnar <mingo@kernel.org>,
Miklos Szeredi <mszeredi@redhat.com>,
Larry Woodman <lwoodman@redhat.com>,
"Wangkai (Kevin,C)" <wangkai86@huawei.com>
Subject: Re: [PATCH v6 0/7] fs/dcache: Track & limit # of negative dentries
Date: Fri, 13 Jul 2018 08:46:52 -0700 [thread overview]
Message-ID: <1531496812.3361.9.camel@HansenPartnership.com> (raw)
In-Reply-To: <20180713003614.GW2234@dastard>
On Fri, 2018-07-13 at 10:36 +1000, Dave Chinner wrote:
> On Thu, Jul 12, 2018 at 12:57:15PM -0700, James Bottomley wrote:
> > What surprises me most about this behaviour is the steadiness of
> > the page cache ... I would have thought we'd have shrunk it
> > somewhat given the intense call on the dcache.
>
> Oh, good, the page cache vs superblock shrinker balancing still
> protects the working set of each cache the way it's supposed to
> under heavy single cache pressure. :)
Well, yes, but my expectation is most of the page cache is clean, so
easily reclaimable. I suppose part of my surprise is that I expected
us to reclaim the clean caches first before we started pushing out the
dirty stuff and reclaiming it. I'm not saying it's a bad thing, just
saying I didn't expect us to make such good decisions under the
parameters of this test.
> Keep in mind that the amount of work slab cache shrinkers perform is
> directly proportional to the amount of page cache reclaim that is
> performed and the size of the slab cache being reclaimed. IOWs,
> under a "single cache pressure" workload we should be directing
> reclaim work to the huge cache creating the pressure and do very
> little reclaim from other caches....
That definitely seems to happen. The thing I was most surprised about
is the steady pushing of anonymous objects to swap. I agree the dentry
cache doesn't seem to be growing hugely after the initial jump, so it
seems to be the largest source of reclaim.
> [ What follows from here is conjecture, but is based on what I've
> seen in the past 10+ years on systems with large numbers of negative
> dentries and fragmented dentry/inode caches. ]
OK, so I fully agree with the concern about pathological object vs page
freeing problems (I referred to it previously). However, I did think
the compaction work that's been ongoing in mm was supposed to help
here?
James
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WARNING: multiple messages have this Message-ID (diff)
From: James Bottomley <James.Bottomley@HansenPartnership.com>
To: Dave Chinner <david@fromorbit.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Matthew Wilcox <willy@infradead.org>,
Waiman Long <longman@redhat.com>,
Michal Hocko <mhocko@kernel.org>,
Al Viro <viro@zeniv.linux.org.uk>,
Jonathan Corbet <corbet@lwn.net>,
"Luis R. Rodriguez" <mcgrof@kernel.org>,
Kees Cook <keescook@chromium.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
linux-mm <linux-mm@kvack.org>,
"open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
Jan Kara <jack@suse.cz>,
Paul McKenney <paulmck@linux.vnet.ibm.com>,
Andrew Morton <akpm@linux-foundation.org>,
Ingo Molnar <mingo@kernel.org>,
Miklos Szeredi <mszeredi@redhat.com>,
Larry Woodman <lwoodman@redhat.com>,
"Wangkai (Kevin,C)" <wangkai86@huawei.com>
Subject: Re: [PATCH v6 0/7] fs/dcache: Track & limit # of negative dentries
Date: Fri, 13 Jul 2018 08:46:52 -0700 [thread overview]
Message-ID: <1531496812.3361.9.camel@HansenPartnership.com> (raw)
In-Reply-To: <20180713003614.GW2234@dastard>
On Fri, 2018-07-13 at 10:36 +1000, Dave Chinner wrote:
> On Thu, Jul 12, 2018 at 12:57:15PM -0700, James Bottomley wrote:
> > What surprises me most about this behaviour is the steadiness of
> > the page cache ... I would have thought we'd have shrunk it
> > somewhat given the intense call on the dcache.
>
> Oh, good, the page cache vs superblock shrinker balancing still
> protects the working set of each cache the way it's supposed to
> under heavy single cache pressure. :)
Well, yes, but my expectation is most of the page cache is clean, so
easily reclaimable. I suppose part of my surprise is that I expected
us to reclaim the clean caches first before we started pushing out the
dirty stuff and reclaiming it. I'm not saying it's a bad thing, just
saying I didn't expect us to make such good decisions under the
parameters of this test.
> Keep in mind that the amount of work slab cache shrinkers perform is
> directly proportional to the amount of page cache reclaim that is
> performed and the size of the slab cache being reclaimed.A A IOWs,
> under a "single cache pressure" workload we should be directing
> reclaim work to the huge cache creating the pressure and do very
> little reclaim from other caches....
That definitely seems to happen. The thing I was most surprised about
is the steady pushing of anonymous objects to swap. I agree the dentry
cache doesn't seem to be growing hugely after the initial jump, so it
seems to be the largest source of reclaim.
> [ What follows from here is conjecture, but is based on what I've
> seen in the past 10+ years on systems with large numbers of negative
> dentries and fragmented dentry/inode caches. ]
OK, so I fully agree with the concern about pathological object vs page
freeing problems (I referred to it previously). However, I did think
the compaction work that's been ongoing in mm was supposed to help
here?
James
next prev parent reply other threads:[~2018-07-13 15:46 UTC|newest]
Thread overview: 114+ 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 ` Waiman Long
2018-07-06 19:32 ` [PATCH v6 1/7] fs/dcache: Track & report number " Waiman Long
2018-07-06 19:32 ` 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 ` Waiman Long
2018-07-06 19:32 ` [PATCH v6 3/7] fs/dcache: Enable automatic pruning of " Waiman Long
2018-07-06 19:32 ` 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 ` 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 ` 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 ` 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 19:32 ` Waiman Long
2018-07-06 21:54 ` Eric Biggers
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
2018-07-06 22:28 ` Al Viro
2018-07-07 3:02 ` Waiman Long
2018-07-07 3:02 ` Waiman Long
2018-07-09 8:19 ` Michal Hocko
2018-07-09 8:19 ` Michal Hocko
2018-07-09 16:01 ` Waiman Long
2018-07-09 16:01 ` Waiman Long
2018-07-10 14:27 ` Michal Hocko
2018-07-10 14:27 ` Michal Hocko
2018-07-10 16:09 ` Waiman Long
2018-07-10 16:09 ` Waiman Long
2018-07-11 10:21 ` Michal Hocko
2018-07-11 10:21 ` Michal Hocko
2018-07-11 15:13 ` Waiman Long
2018-07-11 15:13 ` Waiman Long
2018-07-11 17:42 ` James Bottomley
2018-07-11 17:42 ` James Bottomley
2018-07-11 17:42 ` James Bottomley
2018-07-11 19:07 ` Waiman Long
2018-07-11 19:07 ` Waiman Long
2018-07-11 19:21 ` James Bottomley
2018-07-11 19:21 ` James Bottomley
2018-07-11 19:21 ` James Bottomley
2018-07-11 19:21 ` James Bottomley
2018-07-12 15:54 ` Waiman Long
2018-07-12 15:54 ` Waiman Long
2018-07-12 16:04 ` James Bottomley
2018-07-12 16:04 ` James Bottomley
2018-07-12 16:04 ` James Bottomley
2018-07-12 16:04 ` James Bottomley
2018-07-12 16:26 ` Waiman Long
2018-07-12 16:26 ` Waiman Long
2018-07-12 17:33 ` James Bottomley
2018-07-12 17:33 ` James Bottomley
2018-07-12 17:33 ` James Bottomley
2018-07-12 17:33 ` James Bottomley
2018-07-13 15:32 ` Waiman Long
2018-07-13 15:32 ` Waiman Long
2018-07-12 16:49 ` Matthew Wilcox
2018-07-12 16:49 ` Matthew Wilcox
2018-07-12 17:21 ` James Bottomley
2018-07-12 17:21 ` James Bottomley
2018-07-12 17:21 ` James Bottomley
2018-07-12 17:21 ` James Bottomley
2018-07-12 18:06 ` Linus Torvalds
2018-07-12 19:57 ` James Bottomley
2018-07-12 19:57 ` James Bottomley
2018-07-12 19:57 ` James Bottomley
2018-07-12 19:57 ` James Bottomley
2018-07-13 0:36 ` Dave Chinner
2018-07-13 0:36 ` Dave Chinner
2018-07-13 15:46 ` James Bottomley [this message]
2018-07-13 15:46 ` James Bottomley
2018-07-13 15:46 ` James Bottomley
2018-07-13 15:46 ` James Bottomley
2018-07-13 23:17 ` Dave Chinner
2018-07-13 23:17 ` Dave Chinner
2018-07-13 23:17 ` Dave Chinner
2018-07-13 23:17 ` Dave Chinner
2018-07-16 9:10 ` Michal Hocko
2018-07-16 9:10 ` Michal Hocko
2018-07-16 14:42 ` James Bottomley
2018-07-16 14:42 ` James Bottomley
2018-07-16 14:42 ` James Bottomley
2018-07-16 14:42 ` James Bottomley
2018-07-16 9:09 ` Michal Hocko
2018-07-16 9:09 ` Michal Hocko
2018-07-16 9:12 ` Michal Hocko
2018-07-16 9:12 ` Michal Hocko
2018-07-16 12:41 ` Matthew Wilcox
2018-07-16 12:41 ` Matthew Wilcox
2018-07-16 23:40 ` Andrew Morton
2018-07-16 23:40 ` Andrew Morton
2018-07-17 1:30 ` Matthew Wilcox
2018-07-17 1:30 ` Matthew Wilcox
2018-07-17 8:33 ` Michal Hocko
2018-07-17 8:33 ` Michal Hocko
2018-07-19 0:33 ` Dave Chinner
2018-07-19 0:33 ` Dave Chinner
2018-07-19 8:45 ` Michal Hocko
2018-07-19 8:45 ` Michal Hocko
2018-07-19 9:13 ` Jan Kara
2018-07-19 9:13 ` Jan Kara
2018-07-18 18:39 ` Waiman Long
2018-07-18 18:39 ` Waiman Long
2018-07-18 16:17 ` Waiman Long
2018-07-18 16:17 ` Waiman Long
2018-07-19 8:48 ` Michal Hocko
2018-07-19 8:48 ` Michal Hocko
2018-07-12 8:48 ` Michal Hocko
2018-07-12 8:48 ` Michal Hocko
2018-07-12 16:12 ` Waiman Long
2018-07-12 16:12 ` Waiman Long
2018-07-12 23:16 ` Andrew Morton
2018-07-12 23:16 ` Andrew Morton
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