Re: [Xen-devel] [RFC PATCH v1 01/33] mm: introduce common help functions to deal with reserved/managed pages

[Jiang Liu <liuj97@xxxxxxxxx>]

Hi Sam,
        Thanks for review!

On 03/06/2013 03:47 AM, Sam Ravnborg wrote:
> On Tue, Mar 05, 2013 at 10:54:44PM +0800, Jiang Liu wrote:
>> Code to deal with reserved/managed pages are duplicated by many
>> architectures, so introduce common help functions to reduce duplicated
>> code. These common help functions will also be used to concentrate code
>> to modify totalram_pages and zone->managed_pages, which makes the code
>> much more clear.
>>
>> Signed-off-by: Jiang Liu <jiang.liu@xxxxxxxxxx>
>> ---
>>  include/linux/mm.h |   37 +++++++++++++++++++++++++++++++++++++
>>  mm/page_alloc.c    |   20 ++++++++++++++++++++
>>  2 files changed, 57 insertions(+)
>>
>> diff --git a/include/linux/mm.h b/include/linux/mm.h
>> index 7acc9dc..881461c 100644
>> --- a/include/linux/mm.h
>> +++ b/include/linux/mm.h
>> @@ -1295,6 +1295,43 @@ extern void free_area_init_node(int nid, unsigned 
>> long * zones_size,
>>              unsigned long zone_start_pfn, unsigned long *zholes_size);
>>  extern void free_initmem(void);
>>  
>> +/* Help functions to deal with reserved/managed pages. */
>> +extern unsigned long free_reserved_area(unsigned long start, unsigned long 
>> end,
>> +                                    int poison, char *s);
>> +
>> +static inline void adjust_managed_page_count(struct page *page, long count)
>> +{
>> +    totalram_pages += count;
>> +}
> 
> What is the purpose of the unused page argument?
I will be used in a later patch.

> 
>> +
>> +static inline void __free_reserved_page(struct page *page)
>> +{
>> +    ClearPageReserved(page);
>> +    init_page_count(page);
>> +    __free_page(page);
>> +}
> This method is useful for architectures which implment HIGHMEM,
> like 32 bit x86 and 32 bit sparc.
> This calls for a name without underscores.
We will introduce another help function named free_highmem_page()
to free highmem into the buddy system. In normal cases __free_reserved_page()
won't be called directly, it's just used to handle several special cases.

> 
> 
>> +
>> +static inline void free_reserved_page(struct page *page)
>> +{
>> +    __free_reserved_page(page);
>> +    adjust_managed_page_count(page, 1);
>> +}
>> +
>> +static inline void mark_page_reserved(struct page *page)
>> +{
>> +    SetPageReserved(page);
>> +    adjust_managed_page_count(page, -1);
>> +}
>> +
>> +static inline void free_initmem_default(int poison)
>> +{
> 
> Why request user to supply the poison argumet. If this is the default
> implmentation then use the default poison value too (POISON_FREE_INITMEM)
> 
>> +    extern char __init_begin[], __init_end[];
>> +
>> +    free_reserved_area(PAGE_ALIGN((unsigned long)&__init_begin) ,
>> +                       ((unsigned long)&__init_end) & PAGE_MASK,
>> +                       poison, "unused kernel");
>> +}
> 
> 
> Maybe it is just me how is not used to this area of the kernel.
> But a few comments that describe what the purpose is of each
> function would have helped me.
Good suggestion, will add comments for them.

Regards!
Gerry

> 
>       Sam
> 


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