From: "Ted Ts'o" <tytso@mit.edu>
To: Pekka Enberg <penberg@kernel.org>
Cc: Minchan Kim <minchan.kim@gmail.com>,
Christoph Lameter <cl@linux-foundation.org>,
Pekka Enberg <penberg@cs.helsinki.fi>,
Matt Mackall <mpm@selenic.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
Steven Rostedt <rostedt@goodmis.org>,
David Rientjes <rientjes@google.com>,
npiggin@kernel.dk
Subject: Re: Should we be using unlikely() around tests of GFP_ZERO?
Date: Mon, 3 Jan 2011 08:58:15 -0500 [thread overview]
Message-ID: <20110103135815.GA6024@thunk.org> (raw)
In-Reply-To: <AANLkTinz52Ky5BhU-gHq8vx9=1uoN+iuDn1f0C8fnSjQ@mail.gmail.com>
On Mon, Jan 03, 2011 at 09:40:57AM +0200, Pekka Enberg wrote:
> I guess the rationale here is that if you're going to take the hit of
> memset() you can take the hit of unlikely() as well. We're optimizing
> for hot call-sites that allocate a small amount of memory and
> initialize everything themselves. That said, I don't think the
> unlikely() annotation matters much either way and am for removing it
> unless people object to that.
I suspect for many slab caches, all of the slab allocations for a
given slab cache type will have the GFP_ZERO flag passed. So maybe it
would be more efficient to zap the entire page when it is pressed into
service for a particular slab cache, so we can avoid needing to use
memset on a per-object basis?
- Ted
WARNING: multiple messages have this Message-ID (diff)
From: Ted Ts'o <tytso@mit.edu>
To: Pekka Enberg <penberg@kernel.org>
Cc: Minchan Kim <minchan.kim@gmail.com>,
Christoph Lameter <cl@linux-foundation.org>,
Pekka Enberg <penberg@cs.helsinki.fi>,
Matt Mackall <mpm@selenic.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
Steven Rostedt <rostedt@goodmis.org>,
David Rientjes <rientjes@google.com>,
npiggin@kernel.dk
Subject: Re: Should we be using unlikely() around tests of GFP_ZERO?
Date: Mon, 3 Jan 2011 08:58:15 -0500 [thread overview]
Message-ID: <20110103135815.GA6024@thunk.org> (raw)
In-Reply-To: <AANLkTinz52Ky5BhU-gHq8vx9=1uoN+iuDn1f0C8fnSjQ@mail.gmail.com>
On Mon, Jan 03, 2011 at 09:40:57AM +0200, Pekka Enberg wrote:
> I guess the rationale here is that if you're going to take the hit of
> memset() you can take the hit of unlikely() as well. We're optimizing
> for hot call-sites that allocate a small amount of memory and
> initialize everything themselves. That said, I don't think the
> unlikely() annotation matters much either way and am for removing it
> unless people object to that.
I suspect for many slab caches, all of the slab allocations for a
given slab cache type will have the GFP_ZERO flag passed. So maybe it
would be more efficient to zap the entire page when it is pressed into
service for a particular slab cache, so we can avoid needing to use
memset on a per-object basis?
- Ted
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next prev parent reply other threads:[~2011-01-03 14:01 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-01-02 23:48 Should we be using unlikely() around tests of GFP_ZERO? Theodore Ts'o
2011-01-02 23:48 ` Theodore Ts'o
2011-01-03 3:46 ` Minchan Kim
2011-01-03 3:46 ` Minchan Kim
2011-01-03 7:40 ` Pekka Enberg
2011-01-03 7:40 ` Pekka Enberg
2011-01-03 13:45 ` Steven Rostedt
2011-01-03 13:45 ` Steven Rostedt
2011-01-03 14:10 ` Pekka Enberg
2011-01-03 14:10 ` Pekka Enberg
2011-01-03 14:26 ` Steven Rostedt
2011-01-03 14:26 ` Steven Rostedt
2011-01-03 13:58 ` Ted Ts'o [this message]
2011-01-03 13:58 ` Ted Ts'o
2011-01-03 14:09 ` Pekka Enberg
2011-01-03 14:09 ` Pekka Enberg
2011-01-03 17:23 ` Matt Mackall
2011-01-03 17:23 ` Matt Mackall
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