From: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
To: Nitin Gupta <ngupta@vflare.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Seth Jennings <sjenning@linux.vnet.ibm.com>,
Minchan Kim <minchan@kernel.org>,
Dan Magenheimer <dan.magenheimer@oracle.com>,
Andrew Morton <akpm@linux-foundation.org>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH 3/4] zsmalloc use zs_handle instead of void *
Date: Thu, 10 May 2012 13:33:22 -0400 [thread overview]
Message-ID: <20120510173322.GA30481@phenom.dumpdata.com> (raw)
In-Reply-To: <4FABF9D4.8080303@vflare.org>
On Thu, May 10, 2012 at 01:24:36PM -0400, Nitin Gupta wrote:
> On 5/10/12 12:44 PM, Greg Kroah-Hartman wrote:
> >On Thu, May 10, 2012 at 12:29:41PM -0400, Nitin Gupta wrote:
> >>On 5/10/12 11:19 AM, Greg Kroah-Hartman wrote:
> >>>On Thu, May 10, 2012 at 10:11:27AM -0500, Seth Jennings wrote:
> >>>>On 05/10/2012 09:47 AM, Nitin Gupta wrote:
> >>>>
> >>>>>On 5/10/12 10:02 AM, Konrad Rzeszutek Wilk wrote:
> >>>>>>struct zs {
> >>>>>> void *ptr;
> >>>>>>};
> >>>>>>
> >>>>>>And pass that structure around?
> >>>>>>
> >>>>>
> >>>>>A minor problem is that we store this handle value in a radix tree node.
> >>>>>If we wrap it as a struct, then we will not be able to store it directly
> >>>>>in the node -- the node will have to point to a 'struct zs'. This will
> >>>>>unnecessarily waste sizeof(void *) for every object stored.
> >>>>
> >>>>
> >>>>I don't think so. You can use the fact that for a struct zs var,&var
> >>>>and&var->ptr are the same.
> >>>>
> >>>>For the structure above:
> >>>>
> >>>>void * zs_to_void(struct zs *p) { return p->ptr; }
> >>>>struct zs * void_to_zs(void *p) { return (struct zs *)p; }
> >>>
> >>>Do like what the rest of the kernel does and pass around *ptr and use
> >>>container_of to get 'struct zs'. Yes, they resolve to the same pointer
> >>>right now, but you shouldn't "expect" to to be the same.
> >>>
> >>>
> >>
> >>I think we can just use unsigned long as zs handle type since all we
> >>have to do is tell the user that the returned value is not a
> >>pointer. This will be less pretty than a typedef but still better
> >>than a single entry struct + container_of stuff.
> >
> >But then you are casting the thing all around just as much as you were
> >with the void *, right?
> >
> >Making this a "real" structure ensures type safety and lets the compiler
> >find the problems you accidentally create at times :)
> >
>
> If we return a 'struct zs' from zs_malloc then I cannot see how we
> are solving the original problem of storing the handle directly in a
> radix node. If we pass a struct zs we will require pointing radix
> node to this struct, wasting sizeof(void *) for every object. If
> we pass unsigned long, then this problem is solved and it also makes
> it clear that the passed value is not a pointer.
It is the same size: sizeof(struct zs) == sizeof(void *).
When you return the 'struct zs' it will be as if you are returning
a void * pointer.
>
> Its true that making it a real struct would prevent accidental casts
> to void * but due to the above problem, I think we have to stick
> with unsigned long.
>
> Thanks,
> Nitin
next prev parent reply other threads:[~2012-05-10 17:39 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-05-03 6:40 [PATCH 1/4] zsmalloc: rename zspage_order with zspage_pages Minchan Kim
2012-05-03 6:40 ` [PATCH 2/4] zsmalloc: add/fix function comment Minchan Kim
2012-05-03 13:19 ` Nitin Gupta
2012-05-03 6:40 ` [PATCH 3/4] zsmalloc use zs_handle instead of void * Minchan Kim
2012-05-03 13:32 ` Nitin Gupta
2012-05-03 15:23 ` Seth Jennings
2012-05-04 2:24 ` Minchan Kim
2012-05-07 15:01 ` Seth Jennings
2012-05-09 20:19 ` Greg Kroah-Hartman
2012-05-10 2:03 ` Minchan Kim
2012-05-10 14:02 ` Konrad Rzeszutek Wilk
2012-05-10 14:12 ` Greg Kroah-Hartman
2012-05-10 14:47 ` Nitin Gupta
2012-05-10 15:00 ` Minchan Kim
2012-05-10 15:11 ` Seth Jennings
2012-05-10 15:19 ` Minchan Kim
2012-05-10 15:19 ` Greg Kroah-Hartman
2012-05-10 16:29 ` Nitin Gupta
2012-05-10 16:44 ` Greg Kroah-Hartman
2012-05-10 17:24 ` Nitin Gupta
2012-05-10 17:33 ` Konrad Rzeszutek Wilk [this message]
2012-05-10 23:24 ` Minchan Kim
2012-05-10 23:50 ` Dan Magenheimer
2012-05-11 0:14 ` Minchan Kim
2012-05-11 16:31 ` Dan Magenheimer
2012-05-11 19:29 ` Konrad Rzeszutek Wilk
2012-05-11 21:49 ` Seth Jennings
2012-05-14 2:26 ` Minchan Kim
2012-05-11 19:28 ` Konrad Rzeszutek Wilk
2012-05-14 2:18 ` Minchan Kim
2012-05-15 1:57 ` Nitin Gupta
2012-05-15 2:21 ` Minchan Kim
2012-05-15 15:04 ` Konrad Rzeszutek Wilk
2012-05-16 1:36 ` Minchan Kim
2012-05-16 11:06 ` Konrad Rzeszutek Wilk
2012-05-03 6:40 ` [PATCH 4/4] zsmalloc: zsmalloc: align cache line size Minchan Kim
2012-05-03 13:58 ` Nitin Gupta
2012-05-04 2:27 ` Minchan Kim
2012-05-07 7:41 ` Pekka Enberg
2012-05-07 12:40 ` Nitin Gupta
2012-05-08 1:34 ` Minchan Kim
2012-05-08 14:00 ` Dan Magenheimer
2012-05-09 0:58 ` Minchan Kim
2012-05-09 3:08 ` Dan Magenheimer
2012-05-09 4:07 ` Minchan Kim
2012-05-11 0:03 ` Dan Magenheimer
2012-05-11 0:25 ` Minchan Kim
2012-05-11 19:06 ` Konrad Rzeszutek Wilk
2012-05-14 1:55 ` Minchan Kim
2012-05-15 15:18 ` Konrad Rzeszutek Wilk
2012-05-16 1:44 ` Minchan Kim
2012-05-03 13:18 ` [PATCH 1/4] zsmalloc: rename zspage_order with zspage_pages Nitin Gupta
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=20120510173322.GA30481@phenom.dumpdata.com \
--to=konrad.wilk@oracle.com \
--cc=akpm@linux-foundation.org \
--cc=dan.magenheimer@oracle.com \
--cc=gregkh@linuxfoundation.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=minchan@kernel.org \
--cc=ngupta@vflare.org \
--cc=sjenning@linux.vnet.ibm.com \
/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).