On 05.12.18 01:48, Matthew Wilcox wrote:
> On Tue, Dec 04, 2018 at 02:45:26PM -0800, Anthony Yznaga wrote:
>> Certain pages that are never mapped to userspace have a type
>> indicated in the page_type field of their struct pages (e.g. PG_buddy).
>> page_type overlaps with _mapcount so set the count to 0 and avoid
>> calling page_mapcount() for these pages.
>>
>> Signed-off-by: Anthony Yznaga <anthony.yznaga@xxxxxxxxxx>
>> ---
>> fs/proc/page.c | 2 +-
>> include/linux/page-flags.h | 7 +++++++
>> 2 files changed, 8 insertions(+), 1 deletion(-)
>>
>> diff --git a/fs/proc/page.c b/fs/proc/page.c
>> index 6c517b11acf8..40b05e0d4274 100644
>> --- a/fs/proc/page.c
>> +++ b/fs/proc/page.c
>> @@ -46,7 +46,7 @@ static ssize_t kpagecount_read(struct file *file, char __user *buf,
>> ppage = pfn_to_page(pfn);
>> else
>> ppage = NULL;
>> - if (!ppage || PageSlab(ppage))
>> + if (!ppage || PageSlab(ppage) || page_has_type(ppage))
>> pcount = 0;
>> else
>> pcount = page_mapcount(ppage);
>> diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
>> index 50ce1bddaf56..f9a1c50ccefc 100644
>> --- a/include/linux/page-flags.h
>> +++ b/include/linux/page-flags.h
>> @@ -673,10 +673,17 @@ static inline int TestClearPageDoubleMap(struct page *page)
>> #define PG_balloon 0x00000100
>> #define PG_kmemcg 0x00000200
>> #define PG_table 0x00000400
>> +#define PAGE_TYPE_ALL (PG_buddy | PG_balloon | PG_kmemcg | PG_table)
>>
>> #define PageType(page, flag) \
>> ((page->page_type & (PAGE_TYPE_BASE | flag)) == PAGE_TYPE_BASE)
>>
>> +static inline int page_has_type(struct page *page)
>> +{
>> + return (PageType(page, 0) &&
>> + ((page->page_type & PAGE_TYPE_ALL) != PAGE_TYPE_ALL));
>> +}
>> +
>> #define PAGE_TYPE_OPS(uname, lname) \
>
> I think this is a bit complex, and a bit of a pain to update as we add
> new page types. How about this?
>
> return (int)page_type < -128;
>
> (I'm open to appropriate #defines to make this more obvious that it's ~0x7F)
>
There was already a collision on linux-next, where PG_balloon was
renamed to PG_offline.
--
Thanks,
David / dhildenb
