Re: [Xen-devel] [PATCHES v8 1/8] mm: Place unscrubbed pages at the end of pagelist

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 08/18/2017 05:11 AM, Jan Beulich wrote:
>>>> On 16.08.17 at 20:33, <boris.ostrovsky@xxxxxxxxxx> wrote:
>> .. so that it's easy to find pages that need to be scrubbed (those pages are
>> now marked with _PGC_need_scrub bit).
>>
>> We keep track of the first unscrubbed page in a page buddy using first_dirty
>> field. For now it can have two values, 0 (whole buddy needs scrubbing) or
>> INVALID_DIRTY_IDX (the buddy does not need to be scrubbed). Subsequent 
>> patches
>> will allow scrubbing to be interrupted, resulting in first_dirty taking any
>> value.
>>
>> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
> Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
> with one remark:
>
>> --- a/xen/common/page_alloc.c
>> +++ b/xen/common/page_alloc.c
>> @@ -261,7 +261,11 @@ void __init init_boot_pages(paddr_t ps, paddr_t pe)
>>  #ifdef CONFIG_X86
>>      const unsigned long *badpage = NULL;
>>      unsigned int i, array_size;
>> +
>> +    BUILD_BUG_ON(8 * sizeof(((struct page_info *)0)->u.free.first_dirty) <
>> +                 MAX_ORDER + 1);
>>  #endif
>> +    BUILD_BUG_ON(sizeof(((struct page_info *)0)->u) != sizeof(unsigned 
>> long));
> As I'm generally opposed to casts whenever one can get away
> without, I dislike these as well. In the case here, short of a local
> variable of suitable type, I'd suggest using frame_table instead
> of the open-coded cast. If you're fine with that, this can easily
> be done while committing.

Sure.


-boris

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