From: Tejun Heo <tj@kernel.org>
To: Christoph Lameter <cl@linux.com>
Cc: Dmitry Antipov <dmitry.antipov@linaro.org>,
Rusty Russell <rusty@rustcorp.com.au>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
patches@linaro.org, linaro-dev@lists.linaro.org
Subject: Re: [PATCH 1/3] percpu: use ZERO_SIZE_PTR / ZERO_OR_NULL_PTR
Date: Mon, 30 Jan 2012 10:02:24 -0800 [thread overview]
Message-ID: <20120130180224.GH3355@google.com> (raw)
In-Reply-To: <alpine.DEB.2.00.1201301156530.28693@router.home>
Hello,
On Mon, Jan 30, 2012 at 11:58:52AM -0600, Christoph Lameter wrote:
> > No, NULL is never gonna be a valid return from any allocator including
> > percpu. Percpu allocator doesn't and will never do so.
>
> How do you prevent the percpu allocator from returning NULL? I thought the
> per cpu offsets can wrap around?
I thought it didn't. I rememer thinking about this and determining
that NULL can't be allocated for dynamic addresses. Maybe I'm
imagining things. Anyways, if it can return NULL for valid
allocation, it is a bug and should be fixed.
> > I'm saying we don't have this for ZERO_SIZE_PTR in any meaningful way
> > at this point. If somebody wants to implement it properly, please
> > feel free to, but simply applying ZERO_SIZE_PTR without other changes
> > doesn't make any sense.
>
> We have no clean notion of how a percpu pointer needs to be handled. Both
> ways of handling things have drawbacks.
We don't have returned addr >= PAGE_SIZE guarantee yet but I'm fairly
sure that's the only acceptable direction if we want any improvement
in this area.
Thanks.
--
tejun
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WARNING: multiple messages have this Message-ID (diff)
From: Tejun Heo <tj@kernel.org>
To: Christoph Lameter <cl@linux.com>
Cc: Dmitry Antipov <dmitry.antipov@linaro.org>,
Rusty Russell <rusty@rustcorp.com.au>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
patches@linaro.org, linaro-dev@lists.linaro.org
Subject: Re: [PATCH 1/3] percpu: use ZERO_SIZE_PTR / ZERO_OR_NULL_PTR
Date: Mon, 30 Jan 2012 10:02:24 -0800 [thread overview]
Message-ID: <20120130180224.GH3355@google.com> (raw)
In-Reply-To: <alpine.DEB.2.00.1201301156530.28693@router.home>
Hello,
On Mon, Jan 30, 2012 at 11:58:52AM -0600, Christoph Lameter wrote:
> > No, NULL is never gonna be a valid return from any allocator including
> > percpu. Percpu allocator doesn't and will never do so.
>
> How do you prevent the percpu allocator from returning NULL? I thought the
> per cpu offsets can wrap around?
I thought it didn't. I rememer thinking about this and determining
that NULL can't be allocated for dynamic addresses. Maybe I'm
imagining things. Anyways, if it can return NULL for valid
allocation, it is a bug and should be fixed.
> > I'm saying we don't have this for ZERO_SIZE_PTR in any meaningful way
> > at this point. If somebody wants to implement it properly, please
> > feel free to, but simply applying ZERO_SIZE_PTR without other changes
> > doesn't make any sense.
>
> We have no clean notion of how a percpu pointer needs to be handled. Both
> ways of handling things have drawbacks.
We don't have returned addr >= PAGE_SIZE guarantee yet but I'm fairly
sure that's the only acceptable direction if we want any improvement
in this area.
Thanks.
--
tejun
next prev parent reply other threads:[~2012-01-30 18:02 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-01-30 8:37 [PATCH 1/3] percpu: use ZERO_SIZE_PTR / ZERO_OR_NULL_PTR Dmitry Antipov
2012-01-30 8:37 ` Dmitry Antipov
2012-01-30 16:15 ` Christoph Lameter
2012-01-30 16:15 ` Christoph Lameter
2012-01-30 17:15 ` Tejun Heo
2012-01-30 17:15 ` Tejun Heo
2012-01-30 17:19 ` Tejun Heo
2012-01-30 17:19 ` Tejun Heo
2012-01-30 17:22 ` Christoph Lameter
2012-01-30 17:22 ` Christoph Lameter
2012-01-30 17:33 ` Tejun Heo
2012-01-30 17:33 ` Tejun Heo
2012-01-30 17:35 ` Christoph Lameter
2012-01-30 17:35 ` Christoph Lameter
2012-01-30 17:22 ` Christoph Lameter
2012-01-30 17:22 ` Christoph Lameter
2012-01-30 17:42 ` Tejun Heo
2012-01-30 17:42 ` Tejun Heo
2012-01-30 17:52 ` Christoph Lameter
2012-01-30 17:52 ` Christoph Lameter
2012-01-30 17:54 ` Tejun Heo
2012-01-30 17:54 ` Tejun Heo
2012-01-30 17:58 ` Christoph Lameter
2012-01-30 17:58 ` Christoph Lameter
2012-01-30 18:02 ` Tejun Heo [this message]
2012-01-30 18:02 ` Tejun Heo
2012-01-30 18:12 ` Christoph Lameter
2012-01-30 18:12 ` Christoph Lameter
2012-01-30 18:16 ` Tejun Heo
2012-01-30 18:16 ` Tejun Heo
2012-01-31 4:48 ` Rusty Russell
2012-01-31 4:48 ` Rusty Russell
2012-01-30 18:13 ` Tejun Heo
2012-01-30 18:13 ` Tejun Heo
2012-01-30 18:15 ` Christoph Lameter
2012-01-30 18:15 ` Christoph Lameter
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