On Fri, Jan 19, 2018 at 4:49 AM, Kirill A. Shutemov kirill.shutemov@linux.intel.com wrote:
if (pfn < page_to_pfn(pvmw->page))return false;/* THP can be referenced by any subpage */if (pfn - page_to_pfn(pvmw->page) >= hpage_nr_pages(pvmw->page))return false;
Is gcc actually clever enough to merge these? The "page_to_pfn()" logic can be pretty expensive (exactly for the sparsemem case, but per-node DISCOTIGMEM has some complexity too.
So I'd prefer to make that explicit, perhaps by having a helper function that does this something like
static inline bool pfn_in_hpage(unsigned long pfn, struct page *hpage) { unsigned long hpage_pfn = page_to_pfn(hpage);
return pfn >= hpage_pfn && pfn - hpage_pfn < hpage_nr_pages(hpage); }
and then just use
return pfn_in_hpage(pfn, pvmw->page);
in that caller. Hmm? Wouldn't that be more legible, and avoid the repeated pvmw->page and page_to_pfn() cases?
Even if maybe gcc can do the CSE and turn it all into the same thing in the end..
Linus