On Thu, Oct 09, 2014 at 09:36:30AM -0700, Dave Hansen wrote:
> On 10/09/2014 02:19 AM, Fengwei Yin wrote:
> > diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> > index 80ca4fb..8550b27 100644
> > --- a/fs/proc/task_mmu.c
> > +++ b/fs/proc/task_mmu.c
> > @@ -476,7 +476,7 @@ static void smaps_pte_entry(pte_t ptent, unsigned long addr,
> > mss->nonlinear += ptent_size;
> > }
> >
> > - if (!page)
> > + if (!page || is_huge_zero_page(page))
> > return;
>
> This really seems like a bit of a hack. A normal (small) zero page
> won't make it to this point because of the vm_normal_page() check in
> smaps_pte_entry() which hits the _PAGE_SPECIAL bit in the pte.
>
> Is there a reason we can't set _PAGE_SPECIAL on the huge_zero_page ptes?
> If we did that, we wouldn't need a special case here.
>
> If we can't do that for some reason, can we at least teach
> vm_normal_page() about the huge_zero_page in some other way?
I suppose _PAGE_SPECIAL can't work. Two reasons:
1. Not all arch have HAVE_PTE_SPECIAL set. So always need another way to
handle the arch which has no PTE_SPECIAL.
2. _PAGE_SPECIAL is just for PTE now. If want to add it for huge page,
we need to introduce pmd_mkspecial() thing which I don't think it's
worth to do now (unless you want it. :)).
Yes. We could move the check to vm_normal_page(). But it still needs
export functions from huge_memory.c.
Please check the new patch.
>
> > if (PageAnon(page))
> > @@ -516,7 +516,8 @@ static int smaps_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
> > if (pmd_trans_huge_lock(pmd, vma, &ptl) == 1) {
> > smaps_pte_entry(*(pte_t *)pmd, addr, HPAGE_PMD_SIZE, walk);
> > spin_unlock(ptl);
> > - mss->anonymous_thp += HPAGE_PMD_SIZE;
> > + if (!is_huge_zero_pmd(*pmd))
> > + mss->anonymous_thp += HPAGE_PMD_SIZE;
> > return 0;
> > }
>
> How about we just move this hunk in to smaps_pte_entry()? Something
> along these lines:
>
> ...
> if (PageAnon(page)) {
> mss->anonymous += ptent_size;
> + if (PageTransHuge(page))
> + mss->anonymous_thp += ptent_size;
> }
Done.
>
> If we do that, plus teaching vm_normal_page() about huge_zero_pages, it
> will help keep the hacks and the extra code due to huge pages to a miniumum.
>
> > diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
> > index 63579cb..758f569 100644
> > --- a/include/linux/huge_mm.h
> > +++ b/include/linux/huge_mm.h
> > @@ -34,6 +34,10 @@ extern int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
> > unsigned long addr, pgprot_t newprot,
> > int prot_numa);
> >
> > +extern bool is_huge_zero_page(struct page *page);
> > +
> > +extern bool is_huge_zero_pmd(pmd_t pmd);
> > +
> > enum transparent_hugepage_flag {
> > TRANSPARENT_HUGEPAGE_FLAG,
> > TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
> > diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> > index d9a21d06..bedc3ae 100644
> > --- a/mm/huge_memory.c
> > +++ b/mm/huge_memory.c
> > @@ -173,12 +173,12 @@ static int start_khugepaged(void)
> > static atomic_t huge_zero_refcount;
> > static struct page *huge_zero_page __read_mostly;
> >
> > -static inline bool is_huge_zero_page(struct page *page)
> > +bool is_huge_zero_page(struct page *page)
> > {
> > return ACCESS_ONCE(huge_zero_page) == page;
> > }
> >
> > -static inline bool is_huge_zero_pmd(pmd_t pmd)
> > +bool is_huge_zero_pmd(pmd_t pmd)
> > {
> > return is_huge_zero_page(pmd_page(pmd));
> > }
>
> ^^^ And all these exports.
A new function is_huge_zero_pfn() is added to mm/huge_memory.c
and exported.
Thanks.
>From 4e7bdd5bc22874175982ab50303eab32843c753c Mon Sep 17 00:00:00 2001
From: Fengwei Yin <yfw.kernel@xxxxxxxxx>
Date: Thu, 9 Oct 2014 22:20:58 +0800
Subject: [PATCH] smaps should deal with huge zero page exactly same as normal
zero page.
Signed-off-by: Fengwei Yin <yfw.kernel@xxxxxxxxx>
---
fs/proc/task_mmu.c | 6 ++++--
include/linux/huge_mm.h | 2 ++
mm/huge_memory.c | 5 +++++
mm/memory.c | 4 ++++
4 files changed, 15 insertions(+), 2 deletions(-)
diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index c341568..fb19c0c 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -471,8 +471,11 @@ static void smaps_pte_entry(pte_t ptent, unsigned long addr,
if (!page)
return;
- if (PageAnon(page))
+ if (PageAnon(page)) {
mss->anonymous += ptent_size;
+ if (PageTransHuge(page))
+ mss->anonymous_thp += HPAGE_PMD_SIZE;
+ }
if (page->index != pgoff)
mss->nonlinear += ptent_size;
@@ -508,7 +511,6 @@ static int smaps_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
if (pmd_trans_huge_lock(pmd, vma, &ptl) == 1) {
smaps_pte_entry(*(pte_t *)pmd, addr, HPAGE_PMD_SIZE, walk);
spin_unlock(ptl);
- mss->anonymous_thp += HPAGE_PMD_SIZE;
return 0;
}
diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index 63579cb..9bf6263 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -34,6 +34,8 @@ extern int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
unsigned long addr, pgprot_t newprot,
int prot_numa);
+extern bool is_huge_zero_pfn(unsigned long pfn);
+
enum transparent_hugepage_flag {
TRANSPARENT_HUGEPAGE_FLAG,
TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index f8ffd94..71ca4ed 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -183,6 +183,11 @@ static inline bool is_huge_zero_pmd(pmd_t pmd)
return is_huge_zero_page(pmd_page(pmd));
}
+inline bool is_huge_zero_pfn(unsigned long pfn)
+{
+ return is_huge_zero_page(pfn_to_page(pfn));
+}
+
static struct page *get_huge_zero_page(void)
{
struct page *zero_page;
diff --git a/mm/memory.c b/mm/memory.c
index e229970..5f5ecbc 100644
--- 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;
+
/*
* NOTE! We still have PageReserved() pages in the page tables.
* eg. VDSO mappings can cause them to exist.
--
2.0.1