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From: Nitin Gupta <ngupta@vflare.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>,
	Minchan Kim <minchan@kernel.org>,
	Robert Jennings <rcj@linux.vnet.ibm.com>,
	linux-mm@kvack.org, devel@driverdev.osuosl.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/4] zsmalloc: remove x86 dependency
Date: Wed, 11 Jul 2012 15:42:40 -0700	[thread overview]
Message-ID: <CAPkvG_fejGCrS9u3Mg-ic1B_ar5qdyCSKSQtweijwaZ5mou=dw@mail.gmail.com> (raw)
In-Reply-To: <4FFDE2E2.7050901@linux.vnet.ibm.com>

On Wed, Jul 11, 2012 at 1:32 PM, Seth Jennings
<sjenning@linux.vnet.ibm.com> wrote:
> On 07/11/2012 01:26 PM, Nitin Gupta wrote:
>> On 07/02/2012 02:15 PM, Seth Jennings wrote:
>>> This patch replaces the page table assisted object mapping
>>> method, which has x86 dependencies, with a arch-independent
>>> method that does a simple copy into a temporary per-cpu
>>> buffer.
>>>
>>> While a copy seems like it would be worse than mapping the pages,
>>> tests demonstrate the copying is always faster and, in the case of
>>> running inside a KVM guest, roughly 4x faster.
>>>
>>> Signed-off-by: Seth Jennings <sjenning@linux.vnet.ibm.com>
>>> ---
>>>  drivers/staging/zsmalloc/Kconfig         |    4 --
>>>  drivers/staging/zsmalloc/zsmalloc-main.c |   99 +++++++++++++++++++++---------
>>>  drivers/staging/zsmalloc/zsmalloc_int.h  |    5 +-
>>>  3 files changed, 72 insertions(+), 36 deletions(-)
>>>
>>
>>
>>>  struct mapping_area {
>>> -    struct vm_struct *vm;
>>> -    pte_t *vm_ptes[2];
>>> -    char *vm_addr;
>>> +    char *vm_buf; /* copy buffer for objects that span pages */
>>> +    char *vm_addr; /* address of kmap_atomic()'ed pages */
>>>  };
>>>
>>
>> I think we can reduce the copying overhead by not copying an entire
>> compressed object to another (per-cpu) buffer. The basic idea of the
>> method below is to:
>>  - Copy only the amount of data that spills over into the next page
>>  - No need for a separate buffer to copy into
>>
>> Currently, we store objects that split across pages as:
>>
>> +-Page1-+
>> |     |
>> |     |
>> |-------| <-- obj-1 off: 0
>> |<ob1'>       |
>> +-------+ <-- obj-1 off: s'
>>
>> +-Page2-+ <-- obj-1 off: s'
>> |<ob1''>|
>> |-------| <-- obj-1 off: obj1_size, obj-2 off: 0
>> |<ob2>        |
>> |-------| <-- obj-2 off: obj2_size
>> +-------+
>>
>> But now we would store it as:
>>
>> +-Page1-+
>> |     |
>> |-------| <-- obj-1 off: s''
>> |     |
>> |<ob1'>       |
>> +-------+ <-- obj-1 off: obj1_size
>>
>> +-Page2-+ <-- obj-1 off: 0
>> |<ob1''>|
>> |-------| <-- obj-1 off: s'', obj-2 off: 0
>> |<ob2>        |
>> |-------| <-- obj-2 off: obj2_size
>> +-------+
>>
>> When object-1 (ob1) is to be mapped, part (size: s'-0) of object-2 will
>> be swapped with ob1'. This swapping can be done in-place using simple
>> xor swap algorithm. So, after swap, page-1 and page-2 will look like:
>>
>> +-Page1-+
>> |     |
>> |-------| <-- obj-2 off: 0
>> |     |
>> |<ob2''>|
>> +-------+ <-- obj-2 off: (obj1_size - s'')
>>
>> +-Page2-+ <-- obj-1 off: 0
>> |     |
>> |<ob1>        |
>> |-------| <-- obj-1 off: obj1_size, obj-2 off: (obj1_size - s'')
>> |<ob2'>       |
>> +-------+ <-- obj-2 off: obj2_size
>>
>> Now obj-1 lies completely within page-2, so can be kmap'ed as usual. On
>> zs_unmap_object() we would just do the reverse and restore objects as in
>> figure-1.
>
> Hey Nitin, thanks for the feedback.
>
> Correct me if I'm wrong, but it seems like you wouldn't be able to map
> ob2 while ob1 was mapped with this design.  You'd need some sort of
> zspage level protection against concurrent object mappings.  The
> code for that protection might cancel any benefit you would gain by
> doing it this way.
>

Do you think blocking access of just one particular object (or
blocking an entire zspage, for simplicity) for a short time would be
an issue, apart from the complexity of implementing per zspage
locking?

Thanks,
Nitin

WARNING: multiple messages have this Message-ID
From: Nitin Gupta <ngupta@vflare.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>,
	Minchan Kim <minchan@kernel.org>,
	Robert Jennings <rcj@linux.vnet.ibm.com>,
	linux-mm@kvack.org, devel@driverdev.osuosl.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/4] zsmalloc: remove x86 dependency
Date: Wed, 11 Jul 2012 15:42:40 -0700	[thread overview]
Message-ID: <CAPkvG_fejGCrS9u3Mg-ic1B_ar5qdyCSKSQtweijwaZ5mou=dw@mail.gmail.com> (raw)
In-Reply-To: <4FFDE2E2.7050901@linux.vnet.ibm.com>

On Wed, Jul 11, 2012 at 1:32 PM, Seth Jennings
<sjenning@linux.vnet.ibm.com> wrote:
> On 07/11/2012 01:26 PM, Nitin Gupta wrote:
>> On 07/02/2012 02:15 PM, Seth Jennings wrote:
>>> This patch replaces the page table assisted object mapping
>>> method, which has x86 dependencies, with a arch-independent
>>> method that does a simple copy into a temporary per-cpu
>>> buffer.
>>>
>>> While a copy seems like it would be worse than mapping the pages,
>>> tests demonstrate the copying is always faster and, in the case of
>>> running inside a KVM guest, roughly 4x faster.
>>>
>>> Signed-off-by: Seth Jennings <sjenning@linux.vnet.ibm.com>
>>> ---
>>>  drivers/staging/zsmalloc/Kconfig         |    4 --
>>>  drivers/staging/zsmalloc/zsmalloc-main.c |   99 +++++++++++++++++++++---------
>>>  drivers/staging/zsmalloc/zsmalloc_int.h  |    5 +-
>>>  3 files changed, 72 insertions(+), 36 deletions(-)
>>>
>>
>>
>>>  struct mapping_area {
>>> -    struct vm_struct *vm;
>>> -    pte_t *vm_ptes[2];
>>> -    char *vm_addr;
>>> +    char *vm_buf; /* copy buffer for objects that span pages */
>>> +    char *vm_addr; /* address of kmap_atomic()'ed pages */
>>>  };
>>>
>>
>> I think we can reduce the copying overhead by not copying an entire
>> compressed object to another (per-cpu) buffer. The basic idea of the
>> method below is to:
>>  - Copy only the amount of data that spills over into the next page
>>  - No need for a separate buffer to copy into
>>
>> Currently, we store objects that split across pages as:
>>
>> +-Page1-+
>> |     |
>> |     |
>> |-------| <-- obj-1 off: 0
>> |<ob1'>       |
>> +-------+ <-- obj-1 off: s'
>>
>> +-Page2-+ <-- obj-1 off: s'
>> |<ob1''>|
>> |-------| <-- obj-1 off: obj1_size, obj-2 off: 0
>> |<ob2>        |
>> |-------| <-- obj-2 off: obj2_size
>> +-------+
>>
>> But now we would store it as:
>>
>> +-Page1-+
>> |     |
>> |-------| <-- obj-1 off: s''
>> |     |
>> |<ob1'>       |
>> +-------+ <-- obj-1 off: obj1_size
>>
>> +-Page2-+ <-- obj-1 off: 0
>> |<ob1''>|
>> |-------| <-- obj-1 off: s'', obj-2 off: 0
>> |<ob2>        |
>> |-------| <-- obj-2 off: obj2_size
>> +-------+
>>
>> When object-1 (ob1) is to be mapped, part (size: s'-0) of object-2 will
>> be swapped with ob1'. This swapping can be done in-place using simple
>> xor swap algorithm. So, after swap, page-1 and page-2 will look like:
>>
>> +-Page1-+
>> |     |
>> |-------| <-- obj-2 off: 0
>> |     |
>> |<ob2''>|
>> +-------+ <-- obj-2 off: (obj1_size - s'')
>>
>> +-Page2-+ <-- obj-1 off: 0
>> |     |
>> |<ob1>        |
>> |-------| <-- obj-1 off: obj1_size, obj-2 off: (obj1_size - s'')
>> |<ob2'>       |
>> +-------+ <-- obj-2 off: obj2_size
>>
>> Now obj-1 lies completely within page-2, so can be kmap'ed as usual. On
>> zs_unmap_object() we would just do the reverse and restore objects as in
>> figure-1.
>
> Hey Nitin, thanks for the feedback.
>
> Correct me if I'm wrong, but it seems like you wouldn't be able to map
> ob2 while ob1 was mapped with this design.  You'd need some sort of
> zspage level protection against concurrent object mappings.  The
> code for that protection might cancel any benefit you would gain by
> doing it this way.
>

Do you think blocking access of just one particular object (or
blocking an entire zspage, for simplicity) for a short time would be
an issue, apart from the complexity of implementing per zspage
locking?

Thanks,
Nitin

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  reply	other threads:[~2012-07-11 22:42 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 [this message]
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
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

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