Hi Nitin, On Fri, Jun 23, 2017 at 12:37 AM, Nitin Gupta <nitin.m.gupta@xxxxxxxxxx> wrote: > Hi Julian, > > > On 6/22/17 3:53 AM, Julian Calaby wrote: >> >> On Thu, Jun 22, 2017 at 7:50 AM, Nitin Gupta <nitin.m.gupta@xxxxxxxxxx> >> wrote: >>> >>> The function assumes that each PMD points to head of a >>> huge page. This is not correct as a PMD can point to >>> start of any 8M region with a, say 256M, hugepage. The >>> fix ensures that it points to the correct head of any PMD >>> huge page. >>> >>> Signed-off-by: Nitin Gupta <nitin.m.gupta@xxxxxxxxxx> >>> --- >>> arch/sparc/mm/gup.c | 2 ++ >>> 1 file changed, 2 insertions(+) >>> >>> diff --git a/arch/sparc/mm/gup.c b/arch/sparc/mm/gup.c >>> index cd0e32b..9116a6f 100644 >>> --- a/arch/sparc/mm/gup.c >>> +++ b/arch/sparc/mm/gup.c >>> @@ -80,6 +80,8 @@ static int gup_huge_pmd(pmd_t *pmdp, pmd_t pmd, >>> unsigned long addr, >>> refs = 0; >>> head = pmd_page(pmd); >>> page = head + ((addr & ~PMD_MASK) >> PAGE_SHIFT); >>> + if (PageTail(head)) >>> + head = compound_head(head); >> >> Stupid question: shouldn't this go before the page calculation? > > > No, it should be after page calculation: First, 'head' points to base of > the PMD page, then 'page' points to an offset within that page. Finally, > we make sure that head variable points to head of the compound page > which contains the addr. Thanks for the explanation, that makes a bit more sense to me. > I think confusion comes from the use of 'head' for pointing to a > non-head page. So, maybe it would be more clear to write that part > of the function this way: > > page = pmd_page(pmd) + ((addr & ~PMD_MASK) >> PAGE_SHIFT); > head = compound_head(page); More verbose variable names would help too. =) Thanks, -- Julian Calaby Email: julian.calaby@xxxxxxxxx Profile: http://www.google.com/profiles/julian.calaby/ -- To unsubscribe from this list: send the line "unsubscribe sparclinux" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
