All of lore.kernel.org
 help / color / mirror / Atom feed
From: Minchan Kim <minchan@kernel.org>
To: Seth Jennings <sjenning@linux.vnet.ibm.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Dan Magenheimer <dan.magenheimer@oracle.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
	Nitin Gupta <ngupta@vflare.org>,
	Robert Jennings <rcj@linux.vnet.ibm.com>,
	linux-mm@kvack.org, devel@driverdev.osuosl.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 3/4] zsmalloc: add details to zs_map_object boiler plate
Date: Wed, 11 Jul 2012 16:42:29 +0900	[thread overview]
Message-ID: <4FFD2E65.5080307@kernel.org> (raw)
In-Reply-To: <4FFC478C.4050505@linux.vnet.ibm.com>

On 07/11/2012 12:17 AM, Seth Jennings wrote:
> On 07/09/2012 09:35 PM, Minchan Kim wrote:
>> On 07/03/2012 06:15 AM, Seth Jennings wrote:
>>> Add information on the usage limits of zs_map_object()
>>>
>>> Signed-off-by: Seth Jennings <sjenning@linux.vnet.ibm.com>
>>> ---
>>>  drivers/staging/zsmalloc/zsmalloc-main.c |    7 ++++++-
>>>  1 file changed, 6 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/staging/zsmalloc/zsmalloc-main.c b/drivers/staging/zsmalloc/zsmalloc-main.c
>>> index 4942d41..abf7c13 100644
>>> --- a/drivers/staging/zsmalloc/zsmalloc-main.c
>>> +++ b/drivers/staging/zsmalloc/zsmalloc-main.c
>>> @@ -747,7 +747,12 @@ EXPORT_SYMBOL_GPL(zs_free);
>>>   *
>>>   * Before using an object allocated from zs_malloc, it must be mapped using
>>>   * this function. When done with the object, it must be unmapped using
>>> - * zs_unmap_object
>>> + * zs_unmap_object.
>>> + *
>>> + * Only one object can be mapped per cpu at a time. There is no protection
>>> + * against nested mappings.
>>> + *
>>> + * This function returns with preemption and page faults disabled.
>>>  */
>>>  void *zs_map_object(struct zs_pool *pool, unsigned long handle)
>>>  {
>>>
>>
>> The comment is good but I hope we can detect it automatically with DEBUG
>> option. It wouldn't be hard but it's a debug patch so not critical
>> until we receive some report about the bug.
> 
> Yes, we could implement some detection scheme later.
> 
>>
>> The possibility for nesting is that it is used by irq context.
>>
>> A uses the mapping
>> .
>> .
>> .
>> IRQ happen
>> 	B uses the mapping in IRQ context
>> 	.
>> 	.
>> 	.
>>
>> Maybe we need local_irq_save/restore in zs_[un]map_object path.
> 
> I'd rather not disable interrupts since that will create
> unnecessary interrupt latency for all users, even if they

Agreed.
Although we guide k[un]map atomic is so fast, it isn't necessary
to force irq_[enable|disable]. Okay.

> don't need interrupt protection.  If a particular user uses
> zs_map_object() in an interrupt path, it will be up to that
> user to disable interrupts to ensure safety.

Nope. It shouldn't do that.
Any user in interrupt context can't assume that there isn't any other user using per-cpu buffer
right before interrupt happens.

The concern is that if such bug happens, it's very hard to find a bug.
So, how about adding this?

void zs_map_object(...)
{
	BUG_ON(in_interrupt());
}


> 
> Thanks,
> Seth
> 
> 


-- 
Kind regards,
Minchan Kim



WARNING: multiple messages have this Message-ID
From: Minchan Kim <minchan@kernel.org>
To: Seth Jennings <sjenning@linux.vnet.ibm.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Dan Magenheimer <dan.magenheimer@oracle.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
	Nitin Gupta <ngupta@vflare.org>,
	Robert Jennings <rcj@linux.vnet.ibm.com>,
	linux-mm@kvack.org, devel@driverdev.osuosl.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 3/4] zsmalloc: add details to zs_map_object boiler plate
Date: Wed, 11 Jul 2012 16:42:29 +0900	[thread overview]
Message-ID: <4FFD2E65.5080307@kernel.org> (raw)
In-Reply-To: <4FFC478C.4050505@linux.vnet.ibm.com>

On 07/11/2012 12:17 AM, Seth Jennings wrote:
> On 07/09/2012 09:35 PM, Minchan Kim wrote:
>> On 07/03/2012 06:15 AM, Seth Jennings wrote:
>>> Add information on the usage limits of zs_map_object()
>>>
>>> Signed-off-by: Seth Jennings <sjenning@linux.vnet.ibm.com>
>>> ---
>>>  drivers/staging/zsmalloc/zsmalloc-main.c |    7 ++++++-
>>>  1 file changed, 6 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/staging/zsmalloc/zsmalloc-main.c b/drivers/staging/zsmalloc/zsmalloc-main.c
>>> index 4942d41..abf7c13 100644
>>> --- a/drivers/staging/zsmalloc/zsmalloc-main.c
>>> +++ b/drivers/staging/zsmalloc/zsmalloc-main.c
>>> @@ -747,7 +747,12 @@ EXPORT_SYMBOL_GPL(zs_free);
>>>   *
>>>   * Before using an object allocated from zs_malloc, it must be mapped using
>>>   * this function. When done with the object, it must be unmapped using
>>> - * zs_unmap_object
>>> + * zs_unmap_object.
>>> + *
>>> + * Only one object can be mapped per cpu at a time. There is no protection
>>> + * against nested mappings.
>>> + *
>>> + * This function returns with preemption and page faults disabled.
>>>  */
>>>  void *zs_map_object(struct zs_pool *pool, unsigned long handle)
>>>  {
>>>
>>
>> The comment is good but I hope we can detect it automatically with DEBUG
>> option. It wouldn't be hard but it's a debug patch so not critical
>> until we receive some report about the bug.
> 
> Yes, we could implement some detection scheme later.
> 
>>
>> The possibility for nesting is that it is used by irq context.
>>
>> A uses the mapping
>> .
>> .
>> .
>> IRQ happen
>> 	B uses the mapping in IRQ context
>> 	.
>> 	.
>> 	.
>>
>> Maybe we need local_irq_save/restore in zs_[un]map_object path.
> 
> I'd rather not disable interrupts since that will create
> unnecessary interrupt latency for all users, even if they

Agreed.
Although we guide k[un]map atomic is so fast, it isn't necessary
to force irq_[enable|disable]. Okay.

> don't need interrupt protection.  If a particular user uses
> zs_map_object() in an interrupt path, it will be up to that
> user to disable interrupts to ensure safety.

Nope. It shouldn't do that.
Any user in interrupt context can't assume that there isn't any other user using per-cpu buffer
right before interrupt happens.

The concern is that if such bug happens, it's very hard to find a bug.
So, how about adding this?

void zs_map_object(...)
{
	BUG_ON(in_interrupt());
}


> 
> Thanks,
> Seth
> 
> 


-- 
Kind regards,
Minchan Kim


--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>

  reply	other threads:[~2012-07-11  7:42 UTC|newest]

Thread overview: 62+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-07-02 21:15 [PATCH 0/4] zsmalloc improvements Seth Jennings
2012-07-02 21:15 ` Seth Jennings
2012-07-02 21:15 ` [PATCH 1/4] zsmalloc: remove x86 dependency Seth Jennings
2012-07-02 21:15   ` Seth Jennings
2012-07-10  2:21   ` Minchan Kim
2012-07-10  2:21     ` Minchan Kim
2012-07-10 15:29     ` Seth Jennings
2012-07-10 15:29       ` Seth Jennings
2012-07-11  7:27       ` Minchan Kim
2012-07-11  7:27         ` Minchan Kim
2012-07-11 18:26   ` Nitin Gupta
2012-07-11 18:26     ` Nitin Gupta
2012-07-11 20:32     ` Seth Jennings
2012-07-11 20:32       ` Seth Jennings
2012-07-11 22:42       ` Nitin Gupta
2012-07-11 22:42         ` Nitin Gupta
2012-07-12  0:23         ` Seth Jennings
2012-07-12  0:23           ` Seth Jennings
2012-07-02 21:15 ` [PATCH 2/4] zsmalloc: add single-page object fastpath in unmap Seth Jennings
2012-07-02 21:15   ` Seth Jennings
2012-07-10  2:25   ` Minchan Kim
2012-07-10  2:25     ` Minchan Kim
2012-07-02 21:15 ` [PATCH 3/4] zsmalloc: add details to zs_map_object boiler plate Seth Jennings
2012-07-02 21:15   ` Seth Jennings
2012-07-10  2:35   ` Minchan Kim
2012-07-10  2:35     ` Minchan Kim
2012-07-10 15:17     ` Seth Jennings
2012-07-10 15:17       ` Seth Jennings
2012-07-11  7:42       ` Minchan Kim [this message]
2012-07-11  7:42         ` Minchan Kim
2012-07-11 14:15         ` Seth Jennings
2012-07-11 14:15           ` Seth Jennings
2012-07-12  1:15           ` Minchan Kim
2012-07-12  1:15             ` Minchan Kim
2012-07-12 19:54             ` Dan Magenheimer
2012-07-12 19:54               ` Dan Magenheimer
2012-07-12 22:46               ` Dan Magenheimer
2012-07-12 22:46                 ` Dan Magenheimer
2012-07-02 21:15 ` [PATCH 4/4] zsmalloc: add mapping modes Seth Jennings
2012-07-02 21:15   ` Seth Jennings
2012-07-04  5:33 ` [PATCH 0/4] zsmalloc improvements Minchan Kim
2012-07-04  5:33   ` Minchan Kim
2012-07-04 20:43 ` Konrad Rzeszutek Wilk
2012-07-04 20:43   ` Konrad Rzeszutek Wilk
2012-07-06 15:07   ` Seth Jennings
2012-07-06 15:07     ` Seth Jennings
2012-07-09 13:58     ` Seth Jennings
2012-07-09 13:58       ` Seth Jennings
2012-07-11 19:42       ` Konrad Rzeszutek Wilk
2012-07-11 19:42         ` Konrad Rzeszutek Wilk
2012-07-11 20:48         ` Seth Jennings
2012-07-11 20:48           ` Seth Jennings
2012-07-12 10:40           ` Konrad Rzeszutek Wilk
2012-07-12 10:40             ` Konrad Rzeszutek Wilk
2012-07-11  7:03 ` Minchan Kim
2012-07-11  7:03   ` Minchan Kim
2012-07-11 14:00   ` Seth Jennings
2012-07-11 14:00     ` Seth Jennings
2012-07-12  1:01     ` Minchan Kim
2012-07-12  1:01       ` Minchan Kim
2012-07-11 19:16   ` Seth Jennings
2012-07-11 19:16     ` Seth Jennings

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=4FFD2E65.5080307@kernel.org \
    --to=minchan@kernel.org \
    --cc=akpm@linux-foundation.org \
    --cc=dan.magenheimer@oracle.com \
    --cc=devel@driverdev.osuosl.org \
    --cc=gregkh@linuxfoundation.org \
    --cc=konrad.wilk@oracle.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-mm@kvack.org \
    --cc=ngupta@vflare.org \
    --cc=rcj@linux.vnet.ibm.com \
    --cc=sjenning@linux.vnet.ibm.com \
    --subject='Re: [PATCH 3/4] zsmalloc: add details to zs_map_object boiler plate' \
    /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

This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.