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: 18+ 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 16:15 ` Christoph Lameter
2012-01-30 17:15 ` Tejun Heo
2012-01-30 17:19 ` Tejun Heo
2012-01-30 17:22 ` Christoph Lameter
2012-01-30 17:33 ` Tejun Heo
2012-01-30 17:35 ` Christoph Lameter
2012-01-30 17:22 ` Christoph Lameter
2012-01-30 17:42 ` Tejun Heo
2012-01-30 17:52 ` Christoph Lameter
2012-01-30 17:54 ` Tejun Heo
2012-01-30 17:58 ` Christoph Lameter
2012-01-30 18:02 ` Tejun Heo [this message]
2012-01-30 18:12 ` Christoph Lameter
2012-01-30 18:16 ` Tejun Heo
2012-01-31 4:48 ` Rusty Russell
2012-01-30 18:13 ` Tejun Heo
2012-01-30 18:15 ` Christoph Lameter
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=20120130180224.GH3355@google.com \
--to=tj@kernel.org \
--cc=cl@linux.com \
--cc=dmitry.antipov@linaro.org \
--cc=linaro-dev@lists.linaro.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=patches@linaro.org \
--cc=rusty@rustcorp.com.au \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
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;
as well as URLs for NNTP newsgroup(s).