* [PATCH] zsmalloc: fix obj_to_head use page_private(page) as value but not pointer
@ 2015-10-05 8:23 Hui Zhu
2015-10-06 10:59 ` Sergey Senozhatsky
2015-10-06 13:54 ` Minchan Kim
0 siblings, 2 replies; 5+ messages in thread
From: Hui Zhu @ 2015-10-05 8:23 UTC (permalink / raw)
To: minchan, ngupta, linux-mm, linux-kernel; +Cc: teawater, Hui Zhu
In function obj_malloc:
if (!class->huge)
/* record handle in the header of allocated chunk */
link->handle = handle;
else
/* record handle in first_page->private */
set_page_private(first_page, handle);
The huge's page save handle to private directly.
But in obj_to_head:
if (class->huge) {
VM_BUG_ON(!is_first_page(page));
return page_private(page);
} else
return *(unsigned long *)obj;
It is used as a pointer.
So change obj_to_head use page_private(page) as value but not pointer
in obj_to_head.
Signed-off-by: Hui Zhu <zhuhui@xiaomi.com>
---
mm/zsmalloc.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index f135b1b..e881d4f 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -824,7 +824,7 @@ static unsigned long obj_to_head(struct size_class *class, struct page *page,
{
if (class->huge) {
VM_BUG_ON(!is_first_page(page));
- return *(unsigned long *)page_private(page);
+ return page_private(page);
} else
return *(unsigned long *)obj;
}
--
1.9.1
^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH] zsmalloc: fix obj_to_head use page_private(page) as value but not pointer
2015-10-05 8:23 [PATCH] zsmalloc: fix obj_to_head use page_private(page) as value but not pointer Hui Zhu
@ 2015-10-06 10:59 ` Sergey Senozhatsky
2015-10-06 13:54 ` Minchan Kim
1 sibling, 0 replies; 5+ messages in thread
From: Sergey Senozhatsky @ 2015-10-06 10:59 UTC (permalink / raw)
To: Hui Zhu
Cc: minchan, linux-mm, linux-kernel, teawater, Andrew Morton,
Sergey Senozhatsky
On (10/05/15 16:23), Hui Zhu wrote:
> In function obj_malloc:
> if (!class->huge)
> /* record handle in the header of allocated chunk */
> link->handle = handle;
> else
> /* record handle in first_page->private */
> set_page_private(first_page, handle);
> The huge's page save handle to private directly.
>
> But in obj_to_head:
> if (class->huge) {
> VM_BUG_ON(!is_first_page(page));
> return page_private(page);
> } else
> return *(unsigned long *)obj;
> It is used as a pointer.
>
um...
obj_to_head() is not for obj_malloc(), but for record_obj() that follows.
handle is a `void *' returned from alloc_handle()->kmem_cache_alloc(), and
casted to 'unsigned long'.
we store obj as:
static void record_obj(unsigned long handle, unsigned long obj)
{
*(unsigned long *)handle = obj;
}
regardless `class->huge'.
and retrieve it as `*(unsigned long *)foo', which is either
`*(unsigned long *)page_private(page)'
or
`*(unsigned long *)obj'
'return p' and `return *p' do slightly different things for pointers.
am I missing something?
-ss
> So change obj_to_head use page_private(page) as value but not pointer
> in obj_to_head.
>
> Signed-off-by: Hui Zhu <zhuhui@xiaomi.com>
> ---
> mm/zsmalloc.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
> index f135b1b..e881d4f 100644
> --- a/mm/zsmalloc.c
> +++ b/mm/zsmalloc.c
> @@ -824,7 +824,7 @@ static unsigned long obj_to_head(struct size_class *class, struct page *page,
> {
> if (class->huge) {
> VM_BUG_ON(!is_first_page(page));
> - return *(unsigned long *)page_private(page);
> + return page_private(page);
> } else
> return *(unsigned long *)obj;
> }
> --
> 1.9.1
>
> --
> 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/ .
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>
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] zsmalloc: fix obj_to_head use page_private(page) as value but not pointer
2015-10-05 8:23 [PATCH] zsmalloc: fix obj_to_head use page_private(page) as value but not pointer Hui Zhu
2015-10-06 10:59 ` Sergey Senozhatsky
@ 2015-10-06 13:54 ` Minchan Kim
2015-10-07 4:44 ` Hui Zhu
2015-10-07 4:45 ` [PATCH v2] " Hui Zhu
1 sibling, 2 replies; 5+ messages in thread
From: Minchan Kim @ 2015-10-06 13:54 UTC (permalink / raw)
To: Hui Zhu
Cc: ngupta, linux-mm, linux-kernel, teawater, Andrew Morton,
Sergey Senozhatsky
Hello,
On Mon, Oct 05, 2015 at 04:23:01PM +0800, Hui Zhu wrote:
> In function obj_malloc:
> if (!class->huge)
> /* record handle in the header of allocated chunk */
> link->handle = handle;
> else
> /* record handle in first_page->private */
> set_page_private(first_page, handle);
> The huge's page save handle to private directly.
>
> But in obj_to_head:
> if (class->huge) {
> VM_BUG_ON(!is_first_page(page));
> return page_private(page);
Typo.
return *(unsigned long*)page_private(page);
Please fix the description.
> } else
> return *(unsigned long *)obj;
> It is used as a pointer.
>
> So change obj_to_head use page_private(page) as value but not pointer
> in obj_to_head.
The reason why there is no problem until now is huge-class page is
born with ZS_FULL so it couldn't be migrated.
Therefore, it shouldn't be real bug in practice.
However, we need this patch for future-work "VM-aware zsmalloced
page migration" to reduce external fragmentation.
>
> Signed-off-by: Hui Zhu <zhuhui@xiaomi.com>
With fixing the comment,
Acked-by: Minchan Kim <minchan@kernel.org>
Thanks for the fix, Hui.
--
Kind regards,
Minchan Kim
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] zsmalloc: fix obj_to_head use page_private(page) as value but not pointer
2015-10-06 13:54 ` Minchan Kim
@ 2015-10-07 4:44 ` Hui Zhu
2015-10-07 4:45 ` [PATCH v2] " Hui Zhu
1 sibling, 0 replies; 5+ messages in thread
From: Hui Zhu @ 2015-10-07 4:44 UTC (permalink / raw)
To: Minchan Kim
Cc: Hui Zhu, ngupta, Linux Memory Management List, linux-kernel,
Andrew Morton, Sergey Senozhatsky
On Tue, Oct 6, 2015 at 9:54 PM, Minchan Kim <minchan@kernel.org> wrote:
> Hello,
>
> On Mon, Oct 05, 2015 at 04:23:01PM +0800, Hui Zhu wrote:
>> In function obj_malloc:
>> if (!class->huge)
>> /* record handle in the header of allocated chunk */
>> link->handle = handle;
>> else
>> /* record handle in first_page->private */
>> set_page_private(first_page, handle);
>> The huge's page save handle to private directly.
>>
>> But in obj_to_head:
>> if (class->huge) {
>> VM_BUG_ON(!is_first_page(page));
>> return page_private(page);
>
> Typo.
> return *(unsigned long*)page_private(page);
>
> Please fix the description.
>
>> } else
>> return *(unsigned long *)obj;
>> It is used as a pointer.
>>
>> So change obj_to_head use page_private(page) as value but not pointer
>> in obj_to_head.
>
> The reason why there is no problem until now is huge-class page is
> born with ZS_FULL so it couldn't be migrated.
> Therefore, it shouldn't be real bug in practice.
> However, we need this patch for future-work "VM-aware zsmalloced
> page migration" to reduce external fragmentation.
>
>>
>> Signed-off-by: Hui Zhu <zhuhui@xiaomi.com>
>
> With fixing the comment,
>
> Acked-by: Minchan Kim <minchan@kernel.org>
>
> Thanks for the fix, Hui.
>
Thanks! I will post a new version.
Best,
Hui
> --
> Kind regards,
> Minchan Kim
^ permalink raw reply [flat|nested] 5+ messages in thread
* [PATCH v2] zsmalloc: fix obj_to_head use page_private(page) as value but not pointer
2015-10-06 13:54 ` Minchan Kim
2015-10-07 4:44 ` Hui Zhu
@ 2015-10-07 4:45 ` Hui Zhu
1 sibling, 0 replies; 5+ messages in thread
From: Hui Zhu @ 2015-10-07 4:45 UTC (permalink / raw)
To: minchan, ngupta, linux-mm, linux-kernel
Cc: teawater, akpm, sergey.senozhatsky, Hui Zhu
In function obj_malloc:
if (!class->huge)
/* record handle in the header of allocated chunk */
link->handle = handle;
else
/* record handle in first_page->private */
set_page_private(first_page, handle);
The huge's page save handle to private directly.
But in obj_to_head:
if (class->huge) {
VM_BUG_ON(!is_first_page(page));
return *(unsigned long *)page_private(page);
} else
return *(unsigned long *)obj;
It is used as a pointer.
The reason why there is no problem until now is huge-class page is
born with ZS_FULL so it couldn't be migrated.
Therefore, it shouldn't be real bug in practice.
However, we need this patch for future-work "VM-aware zsmalloced
page migration" to reduce external fragmentation.
Signed-off-by: Hui Zhu <zhuhui@xiaomi.com>
Acked-by: Minchan Kim <minchan@kernel.org>
---
mm/zsmalloc.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index f135b1b..e881d4f 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -824,7 +824,7 @@ static unsigned long obj_to_head(struct size_class *class, struct page *page,
{
if (class->huge) {
VM_BUG_ON(!is_first_page(page));
- return *(unsigned long *)page_private(page);
+ return page_private(page);
} else
return *(unsigned long *)obj;
}
--
1.9.1
^ permalink raw reply related [flat|nested] 5+ messages in thread
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2015-10-05 8:23 [PATCH] zsmalloc: fix obj_to_head use page_private(page) as value but not pointer Hui Zhu
2015-10-06 10:59 ` Sergey Senozhatsky
2015-10-06 13:54 ` Minchan Kim
2015-10-07 4:44 ` Hui Zhu
2015-10-07 4:45 ` [PATCH v2] " Hui Zhu
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