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From: Nick Piggin <npiggin@gmail.com>
To: Nick Piggin <npiggin@gmail.com>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: Important for fs devs: rcu-walk merged upstream
Date: Wed, 12 Jan 2011 00:06:42 +1100	[thread overview]
Message-ID: <AANLkTimrqb5e9QKT7UFLXtQHap689kSoEZRmLvax5Xm-@mail.gmail.com> (raw)
In-Reply-To: <20110111010800.GE4879@mail.oracle.com>

On Tuesday, January 11, 2011, Joel Becker <jlbec@evilplan.org> wrote:
> On Sat, Jan 08, 2011 at 01:54:47PM +1100, Nick Piggin wrote:
>> The rcu-walk stuff can be more tricky for your filesystem
>> to take advantage of.
>>
>> If you supply a .d_revalidate, .permission, or .check_acl,
>> then path walking is going to be slow and unscalable for
>> you.
>
>         Do you mean "as slow and unscalable as it has always been" or
> "even slower now"?  A quick look suggests the former, but I wanted to be
> sure.

Yeah it should be about the same. Bit more complex code so it might be
a bit slower. A few code and branch and cache improvements so it might
be a bit faster. Refcounts on the same dentry become a bit less
scalable for using lock instead of atomic. On the other hand dropping
the ref on leaf denty doesn't require global lock.

It should not be urgent for 2.6.38.

WARNING: multiple messages have this Message-ID (diff)
From: Nick Piggin <npiggin@gmail.com>
To: Nick Piggin <npiggin@gmail.com>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: Important for fs devs: rcu-walk merged upstream
Date: Wed, 12 Jan 2011 00:06:42 +1100	[thread overview]
Message-ID: <AANLkTimrqb5e9QKT7UFLXtQHap689kSoEZRmLvax5Xm-@mail.gmail.com> (raw)
In-Reply-To: <20110111010800.GE4879@mail.oracle.com>

On Tuesday, January 11, 2011, Joel Becker <jlbec@evilplan.org> wrote:
> On Sat, Jan 08, 2011 at 01:54:47PM +1100, Nick Piggin wrote:
>> The rcu-walk stuff can be more tricky for your filesystem
>> to take advantage of.
>>
>> If you supply a .d_revalidate, .permission, or .check_acl,
>> then path walking is going to be slow and unscalable for
>> you.
>
>         Do you mean "as slow and unscalable as it has always been" or
> "even slower now"?  A quick look suggests the former, but I wanted to be
> sure.

Yeah it should be about the same. Bit more complex code so it might be
a bit slower. A few code and branch and cache improvements so it might
be a bit faster. Refcounts on the same dentry become a bit less
scalable for using lock instead of atomic. On the other hand dropping
the ref on leaf denty doesn't require global lock.

It should not be urgent for 2.6.38.
--
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  reply	other threads:[~2011-01-11 13:06 UTC|newest]

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-01-08  2:54 Important for fs devs: rcu-walk merged upstream Nick Piggin
2011-01-08  9:10 ` Marco Stornelli
2011-01-11  9:57   ` Nick Piggin
2011-01-11  9:57     ` Nick Piggin
2011-01-11 11:08     ` Miklos Szeredi
2011-01-10 14:38 ` J. R. Okajima
2011-01-11 12:57   ` Nick Piggin
2011-01-11 12:57     ` Nick Piggin
2011-01-11  1:08 ` Joel Becker
2011-01-11 13:06   ` Nick Piggin [this message]
2011-01-11 13:06     ` Nick Piggin
2011-01-13 14:58 ` Miklos Szeredi
2011-01-13 16:18   ` Miklos Szeredi
2011-01-14  1:21     ` Nick Piggin
2011-01-14  1:21       ` Nick Piggin
2011-01-14  8:45       ` Miklos Szeredi
2011-01-14  8:45         ` Miklos Szeredi
2011-01-14  8:52         ` Nick Piggin
2011-01-14  8:52           ` Nick Piggin
2011-01-14  9:38           ` Miklos Szeredi
2011-01-14  9:38             ` Miklos Szeredi

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