From: Eric Dumazet <dada1@cosmosbay•com>
To: Al Viro <viro@ZenIV•linux.org.uk>
Cc: Ingo Molnar <mingo@elte•hu>, David Miller <davem@davemloft•net>,
"Rafael J. Wysocki" <rjw@sisk•pl>,
linux-kernel@vger•kernel.org, kernel-testers@vger•kernel.org,
Mike Galbraith <efault@gmx•de>,
Peter Zijlstra <a.p.zijlstra@chello•nl>,
Linux Netdev List <netdev@vger•kernel.org>,
Christoph Lameter <cl@linux-foundation•org>,
Christoph Hellwig <hch@infradead•org>,
rth@twiddle•net, ink@jurassic•park.msu.ru
Subject: Re: [PATCH 6/6] fs: Introduce kern_mount_special() to mount special vfs
Date: Fri, 28 Nov 2008 23:37:43 +0100 [thread overview]
Message-ID: <493072B7.5050308@cosmosbay.com> (raw)
In-Reply-To: <20081128092604.GL28946@ZenIV.linux.org.uk>
Al Viro a écrit :
> On Thu, Nov 27, 2008 at 12:32:59AM +0100, Eric Dumazet wrote:
>> This function arms a flag (MNT_SPECIAL) on the vfs, to avoid
>> refcounting on permanent system vfs.
>> Use this function for sockets, pipes, anonymous fds.
>
> IMO that's pushing it past the point of usefulness; unless you can show
> that this really gives considerable win on pipes et.al. *AND* that it
> doesn't hurt other loads...
Well, if this is the last cache line that might be shared, then yes, numbers can talk.
But coming from 10 to 1 instead of 0 is OK I guess
>
> dput() part: again, I want to see what happens on other loads; it's probably
> fine (and win is certainly more than from mntput() change), but... The
> thing is, atomic_dec_and_lock() in there is often done on dentries with
> d_count > 1 and that's fairly cheap (and doesn't involve contention on
> dcache_lock on sane targets).
>
> FWIW, unless there's a really good reason to do alpha atomic_dec_and_lock()
> in a special way, I'd try to compare with
> if (atomic_add_unless(&dentry->d_count, -1, 1))
> return;
I dont know, but *reading* d_count before trying to write it is expensive
on modern cpus. Oprofile clearly show that on Intel Core2.
Then, *testing* the flag before doing the atomic_something() has the same
problem. Or we should put flag in a different cache line.
I am lazy (time for a sleep here), maybe we are smart here and use a trick like that already ?
atomic_t atomic_read_with_write_intent(atomic_t *v)
{
int val = 0;
/*
* No LOCK prefix here, we only give a write intent hint to cpu
*/
asm volatile("xaddl %0, %1"
: "+r" (val), "+m" (v->counter)
: : "memory");
return val;
}
> if (your flag)
> sod off to special
> spin_lock(&dcache_lock);
> if (atomic_dec_and_test(&dentry->d_count)) {
> spin_unlock(&dcache_lock);
> return;
> }
> the rest as usual
>
next prev parent reply other threads:[~2008-11-28 22:38 UTC|newest]
Thread overview: 75+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <Pine.LNX.4.64.0811201727070.9089@quilx.com>
[not found] ` <20081121083044.GL16242@elte.hu>
[not found] ` <49267694.1030506@cosmosbay.com>
[not found] ` <20081121.010508.40225532.davem@davemloft.net>
[not found] ` <4926AEDB.10007@cosmosbay.com>
[not found] ` <4926AEDB.10007-fPLkHRcR87vqlBn2x/YWAg@public.gmane.org>
2008-11-21 15:13 ` [PATCH] fs: pipe/sockets/anon dentries should not have a parent Eric Dumazet
[not found] ` <4926D022.5060008-fPLkHRcR87vqlBn2x/YWAg@public.gmane.org>
2008-11-21 15:21 ` Ingo Molnar
[not found] ` <20081121152148.GA20388-X9Un+BFzKDI@public.gmane.org>
2008-11-21 15:28 ` Eric Dumazet
[not found] ` <4926D39D.9050603-fPLkHRcR87vqlBn2x/YWAg@public.gmane.org>
2008-11-21 15:34 ` Ingo Molnar
2008-11-26 23:27 ` [PATCH 0/6] fs: Scalability of sockets/pipes allocation/deallocation on SMP Eric Dumazet
2008-11-27 9:39 ` Christoph Hellwig
2008-11-28 18:03 ` Ingo Molnar
[not found] ` <20081128180318.GL10487-X9Un+BFzKDI@public.gmane.org>
2008-11-28 18:47 ` Peter Zijlstra
2008-11-29 6:38 ` Christoph Hellwig
[not found] ` <20081129063816.GA869-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>
2008-11-29 8:07 ` Eric Dumazet
2008-11-29 8:43 ` [PATCH v2 0/5] " Eric Dumazet
2008-12-11 22:38 ` [PATCH v3 0/7] " Eric Dumazet
2008-12-11 22:38 ` [PATCH v3 1/7] fs: Use a percpu_counter to track nr_dentry Eric Dumazet
2007-07-24 1:24 ` Nick Piggin
[not found] ` <49419680.8010409-fPLkHRcR87vqlBn2x/YWAg@public.gmane.org>
2008-12-16 21:04 ` Paul E. McKenney
2008-12-11 22:39 ` [PATCH v3 2/7] fs: Use a percpu_counter to track nr_inodes Eric Dumazet
[not found] ` <4941968E.3020201-fPLkHRcR87vqlBn2x/YWAg@public.gmane.org>
2007-07-24 1:30 ` Nick Piggin
[not found] ` <200707241130.56767.nickpiggin-/E1597aS9LT0CCvOHzKKcA@public.gmane.org>
2008-12-12 5:11 ` Eric Dumazet
2008-12-16 21:10 ` Paul E. McKenney
2008-12-11 22:39 ` [PATCH v3 3/7] fs: Introduce a per_cpu last_ino allocator Eric Dumazet
2007-07-24 1:34 ` Nick Piggin
2008-12-16 21:26 ` Paul E. McKenney
2008-12-11 22:39 ` [PATCH v3 4/7] fs: Introduce SINGLE dentries for pipes, socket, anon fd Eric Dumazet
[not found] ` <494196AA.6080002-fPLkHRcR87vqlBn2x/YWAg@public.gmane.org>
2008-12-16 21:40 ` Paul E. McKenney
2008-12-11 22:40 ` [PATCH v3 5/7] fs: new_inode_single() and iput_single() Eric Dumazet
2008-12-16 21:41 ` Paul E. McKenney
[not found] ` <493100B0.6090104-fPLkHRcR87vqlBn2x/YWAg@public.gmane.org>
2008-12-11 22:40 ` [PATCH v3 6/7] fs: struct file move from call_rcu() to SLAB_DESTROY_BY_RCU Eric Dumazet
2007-07-24 1:13 ` Nick Piggin
2008-12-12 2:50 ` Nick Piggin
2008-12-12 4:45 ` Eric Dumazet
[not found] ` <4941EC65.5040903-fPLkHRcR87vqlBn2x/YWAg@public.gmane.org>
2008-12-12 16:48 ` Eric Dumazet
[not found] ` <494295C6.2020906-fPLkHRcR87vqlBn2x/YWAg@public.gmane.org>
2008-12-13 2:07 ` Christoph Lameter
[not found] ` <Pine.LNX.4.64.0812121958470.15781-dRBSpnHQED8AvxtiuMwx3w@public.gmane.org>
2008-12-17 20:25 ` Eric Dumazet
2008-12-13 1:41 ` Christoph Lameter
2008-12-11 22:41 ` [PATCH v3 7/7] fs: MS_NOREFCOUNT Eric Dumazet
2008-11-29 8:44 ` [PATCH v2 3/5] fs: Introduce a per_cpu last_ino allocator Eric Dumazet
[not found] ` <492DDB6A.8090806-fPLkHRcR87vqlBn2x/YWAg@public.gmane.org>
2008-11-27 1:37 ` [PATCH 0/6] fs: Scalability of sockets/pipes allocation/deallocation on SMP Christoph Lameter
[not found] ` <Pine.LNX.4.64.0811261935330.31159-dRBSpnHQED8AvxtiuMwx3w@public.gmane.org>
2008-11-27 6:27 ` Eric Dumazet
[not found] ` <492E3DEF.8030602-fPLkHRcR87vqlBn2x/YWAg@public.gmane.org>
2008-11-27 14:44 ` Christoph Lameter
2008-11-29 8:43 ` [PATCH v2 1/5] fs: Use a percpu_counter to track nr_dentry Eric Dumazet
2008-11-29 8:43 ` [PATCH v2 2/5] fs: Use a percpu_counter to track nr_inodes Eric Dumazet
2008-11-29 8:44 ` [PATCH v2 4/5] fs: Introduce SINGLE dentries for pipes, socket, anon fd Eric Dumazet
[not found] ` <493100E7.3030907-fPLkHRcR87vqlBn2x/YWAg@public.gmane.org>
2008-11-29 10:38 ` Jörn Engel
[not found] ` <20081129103836.GA11959-PCqxUs/MD9bYtjvyW6yDsg@public.gmane.org>
2008-11-29 11:14 ` Eric Dumazet
2008-11-29 8:45 ` [PATCH v2 5/5] fs: new_inode_single() and iput_single() Eric Dumazet
2008-11-29 11:14 ` Jörn Engel
[not found] ` <20081121153453.GA23713-X9Un+BFzKDI@public.gmane.org>
2008-11-26 23:30 ` [PATCH 1/6] fs: Introduce a per_cpu nr_dentry Eric Dumazet
[not found] ` <492DDC0B.8060804-fPLkHRcR87vqlBn2x/YWAg@public.gmane.org>
2008-11-27 9:41 ` Christoph Hellwig
2008-11-26 23:32 ` [PATCH 4/6] fs: Introduce a per_cpu nr_inodes Eric Dumazet
2008-11-27 9:32 ` Peter Zijlstra
2008-11-27 9:39 ` Peter Zijlstra
2008-11-27 9:48 ` Christoph Hellwig
2008-11-27 10:01 ` Eric Dumazet
2008-11-27 10:07 ` Andi Kleen
2008-11-27 14:46 ` Christoph Lameter
2008-11-26 23:32 ` [PATCH 5/6] fs: Introduce special inodes Eric Dumazet
[not found] ` <492DDC99.5060106-fPLkHRcR87vqlBn2x/YWAg@public.gmane.org>
2008-11-27 8:20 ` David Miller
2008-11-26 23:32 ` [PATCH 3/6] fs: Introduce a per_cpu last_ino allocator Eric Dumazet
[not found] ` <492DDC88.2050305-fPLkHRcR87vqlBn2x/YWAg@public.gmane.org>
2008-11-27 9:46 ` Christoph Hellwig
2008-11-26 23:32 ` [PATCH 6/6] fs: Introduce kern_mount_special() to mount special vfs Eric Dumazet
2008-11-27 9:53 ` Christoph Hellwig
[not found] ` <20081127095321.GE13860-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>
2008-11-27 10:04 ` Eric Dumazet
[not found] ` <492E70B6.70108-fPLkHRcR87vqlBn2x/YWAg@public.gmane.org>
2008-11-27 10:10 ` Christoph Hellwig
[not found] ` <492DDCAB.1070204-fPLkHRcR87vqlBn2x/YWAg@public.gmane.org>
2008-11-27 8:21 ` David Miller
2008-11-28 9:26 ` Al Viro
[not found] ` <20081128092604.GL28946-3bDd1+5oDREiFSDQTTA3OLVCufUGDwFn@public.gmane.org>
2008-11-28 9:34 ` Al Viro
2008-11-28 18:02 ` Ingo Molnar
2008-11-28 18:58 ` Ingo Molnar
[not found] ` <20081128180220.GK10487-X9Un+BFzKDI@public.gmane.org>
2008-11-28 22:20 ` Eric Dumazet
2008-11-28 22:37 ` Eric Dumazet [this message]
2008-11-28 22:43 ` Eric Dumazet
2008-11-21 15:36 ` [PATCH] fs: pipe/sockets/anon dentries should not have a parent Christoph Hellwig
2008-11-21 17:58 ` [PATCH] fs: pipe/sockets/anon dentries should have themselves as parent Eric Dumazet
[not found] ` <4926F6C5.9030108-fPLkHRcR87vqlBn2x/YWAg@public.gmane.org>
2008-11-21 18:43 ` Matthew Wilcox
2008-11-23 3:53 ` Eric Dumazet
Reply instructions:
You may reply publicly 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=493072B7.5050308@cosmosbay.com \
--to=dada1@cosmosbay$(echo .)com \
--cc=a.p.zijlstra@chello$(echo .)nl \
--cc=cl@linux-foundation$(echo .)org \
--cc=davem@davemloft$(echo .)net \
--cc=efault@gmx$(echo .)de \
--cc=hch@infradead$(echo .)org \
--cc=ink@jurassic$(echo .)park.msu.ru \
--cc=kernel-testers@vger$(echo .)kernel.org \
--cc=linux-kernel@vger$(echo .)kernel.org \
--cc=mingo@elte$(echo .)hu \
--cc=netdev@vger$(echo .)kernel.org \
--cc=rjw@sisk$(echo .)pl \
--cc=rth@twiddle$(echo .)net \
--cc=viro@ZenIV$(echo .)linux.org.uk \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox