From: James Bottomley <James.Bottomley@HansenPartnership.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: Waiman Long <longman@redhat.com>,
Michal Hocko <mhocko@kernel.org>,
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>,
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: Thu, 12 Jul 2018 10:21:20 -0700 [thread overview]
Message-ID: <1531416080.18255.8.camel@HansenPartnership.com> (raw)
In-Reply-To: <20180712164932.GA3475@bombadil.infradead.org>
On Thu, 2018-07-12 at 09:49 -0700, Matthew Wilcox wrote:
> On Thu, Jul 12, 2018 at 09:04:54AM -0700, James Bottomley wrote:
[...]
> > The question I'm trying to get an answer to is why does the dentry
> > cache need special limits when the mm handling of the page cache
> > (and other mm caches) just works?
>
> I don't know that it does work. Or that it works well.
I'm not claiming the general heuristics are perfect (in fact I know we
still have a lot of problems with dirty reclaim and writeback). I am
willing to bet that any discussion of the heuristics will get a lot of
opposition if we try to introduce per-object limits for every object.
Our clean cache heuristics are simple: clean caches are easy to reclaim
and are thus treated like free memory (there's little cost to filling
them or reclaiming them again). There is speculation that this
equivalence is problematic because the shrinkers reclaim objects but mm
is looking to reclaim pages and thus you can end up with a few objects
pinning many pages even if the shrinker freed a lot of them.
However, we haven't even reached that level yet ... I'm still
struggling to establish that we have a problem with the behaviour of
the dentry cache under current mm heuristics.
James
WARNING: multiple messages have this Message-ID (diff)
From: James Bottomley <James.Bottomley@HansenPartnership.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: Waiman Long <longman@redhat.com>,
Michal Hocko <mhocko@kernel.org>,
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>,
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: Thu, 12 Jul 2018 10:21:20 -0700 [thread overview]
Message-ID: <1531416080.18255.8.camel@HansenPartnership.com> (raw)
In-Reply-To: <20180712164932.GA3475@bombadil.infradead.org>
On Thu, 2018-07-12 at 09:49 -0700, Matthew Wilcox wrote:
> On Thu, Jul 12, 2018 at 09:04:54AM -0700, James Bottomley wrote:
[...]
> > The question I'm trying to get an answer to is why does the dentry
> > cache need special limits when the mm handling of the page cache
> > (and other mm caches) just works?
>
> I don't know that it does work. Or that it works well.
I'm not claiming the general heuristics are perfect (in fact I know we
still have a lot of problems with dirty reclaim and writeback). I am
willing to bet that any discussion of the heuristics will get a lot of
opposition if we try to introduce per-object limits for every object.
Our clean cache heuristics are simple: clean caches are easy to reclaim
and are thus treated like free memory (there's little cost to filling
them or reclaiming them again). There is speculation that this
equivalence is problematic because the shrinkers reclaim objects but mm
is looking to reclaim pages and thus you can end up with a few objects
pinning many pages even if the shrinker freed a lot of them.
However, we haven't even reached that level yet ... I'm still
struggling to establish that we have a problem with the behaviour of
the dentry cache under current mm heuristics.
James
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WARNING: multiple messages have this Message-ID (diff)
From: James Bottomley <James.Bottomley@HansenPartnership.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: Waiman Long <longman@redhat.com>,
Michal Hocko <mhocko@kernel.org>,
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>,
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: Thu, 12 Jul 2018 10:21:20 -0700 [thread overview]
Message-ID: <1531416080.18255.8.camel@HansenPartnership.com> (raw)
In-Reply-To: <20180712164932.GA3475@bombadil.infradead.org>
On Thu, 2018-07-12 at 09:49 -0700, Matthew Wilcox wrote:
> On Thu, Jul 12, 2018 at 09:04:54AM -0700, James Bottomley wrote:
[...]
> > The question I'm trying to get an answer to is why does the dentry
> > cache need special limits when the mm handling of the page cache
> > (and other mm caches) just works?
>
> I don't know that it does work.A A Or that it works well.
I'm not claiming the general heuristics are perfect (in fact I know we
still have a lot of problems with dirty reclaim and writeback). I am
willing to bet that any discussion of the heuristics will get a lot of
opposition if we try to introduce per-object limits for every object.
Our clean cache heuristics are simple: clean caches are easy to reclaim
and are thus treated like free memory (there's little cost to filling
them or reclaiming them again). There is speculation that this
equivalence is problematic because the shrinkers reclaim objects but mm
is looking to reclaim pages and thus you can end up with a few objects
pinning many pages even if the shrinker freed a lot of them.
However, we haven't even reached that level yet ... I'm still
struggling to establish that we have a problem with the behaviour of
the dentry cache under current mm heuristics.
James
next prev parent reply other threads:[~2018-07-12 17:21 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 [this message]
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
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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