On Mon, Oct 27, 2014 at 03:17:48PM -0700, Andrew Morton wrote: > On Mon, 27 Oct 2014 23:02:13 +0800 Fengwei Yin <yfw.kernel@xxxxxxxxx> wrote: > > > We could see following memory info in /proc/xxxx/smaps with THP enabled. > > 7bea458b3000-7fea458b3000 r--p 00000000 00:13 39989 /dev/zero > > Size: 4294967296 kB > > Rss: 10612736 kB > > Pss: 10612736 kB > > Shared_Clean: 0 kB > > Shared_Dirty: 0 kB > > Private_Clean: 10612736 kB > > Private_Dirty: 0 kB > > Referenced: 10612736 kB > > Anonymous: 0 kB > > AnonHugePages: 10612736 kB > > Swap: 0 kB > > KernelPageSize: 4 kB > > MMUPageSize: 4 kB > > Locked: 0 kB > > VmFlags: rd mr mw me > > which is wrong becuase just huge_zero_page/normal_zero_page is used for > > /dev/zero. Most of the value should be 0. > > > > This patch detects huge_zero_page (original implementation just detect > > normal_zero_page) and avoids to update the wrong value for huge_zero_page. > > > > ... > > > > --- a/mm/memory.c > > +++ b/mm/memory.c > > @@ -41,6 +41,7 @@ > > #include <linux/kernel_stat.h> > > #include <linux/mm.h> > > #include <linux/hugetlb.h> > > +#include <linux/huge_mm.h> > > #include <linux/mman.h> > > #include <linux/swap.h> > > #include <linux/highmem.h> > > @@ -787,6 +788,9 @@ check_pfn: > > return NULL; > > } > > > > + if (is_huge_zero_pfn(pfn)) > > + return NULL; > > + > > Why this change? > I suppose the huge zero page should have same behavior as normal zero page. vm_normal_page will return NULL if the pte is for normal zero page. This change make it return NULL for huge zero page. > What effect does it have upon vm_normal_page()'s many existing callers? This is good question. I suppose it will not impact existing caller. As I undestand, all other callers just pass real pte to vm_normal_page. They will not go to this "is_huge_zero_pfn" path. The only impact code is in smaps_pte_entry() (fs/proc/task_mmu.c) which is what I want to fix. BTW, the patch doesn't pass build without CONFIG_TRANSPARENT_HUGEPAGE. I will send a new patch. Sorry for this. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>