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SubjectRe: [PATCH 2/8] mm: use walk_page_range() instead of custom page table walking code
On Mon, May 09, 2011 at 04:38:49PM +0900, KOSAKI Motohiro wrote:
> Hello,
>
> sorry for the long delay.

Please, no apologies. Thank you for the review!

> > In the specific case of show_numa_map(), the custom page table walking
> > logic implemented in mempolicy.c does not provide any special service
> > beyond that provided by walk_page_range().
> >
> > Also, converting show_numa_map() to use the generic routine decouples
> > the function from mempolicy.c, allowing it to be moved out of the mm
> > subsystem and into fs/proc.
> >
> > Signed-off-by: Stephen Wilson <wilsons@start.ca>
> > ---
> > mm/mempolicy.c | 53 ++++++++++++++++++++++++++++++++++++++++++++++-------
> > 1 files changed, 46 insertions(+), 7 deletions(-)
> >
> > diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> > index 5bfb03e..dfe27e3 100644
> > --- a/mm/mempolicy.c
> > +++ b/mm/mempolicy.c
> > @@ -2568,6 +2568,22 @@ static void gather_stats(struct page *page, void *private, int pte_dirty)
> > md->node[page_to_nid(page)]++;
> > }
> >
> > +static int gather_pte_stats(pte_t *pte, unsigned long addr,
> > + unsigned long pte_size, struct mm_walk *walk)
> > +{
> > + struct page *page;
> > +
> > + if (pte_none(*pte))
> > + return 0;
> > +
> > + page = pte_page(*pte);
> > + if (!page)
> > + return 0;
>
> original check_pte_range() has following logic.
>
> orig_pte = pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
> do {
> struct page *page;
> int nid;
>
> if (!pte_present(*pte))
> continue;
> page = vm_normal_page(vma, addr, *pte);
> if (!page)
> continue;
> /*
> * vm_normal_page() filters out zero pages, but there might
> * still be PageReserved pages to skip, perhaps in a VDSO.
> * And we cannot move PageKsm pages sensibly or safely yet.
> */
> if (PageReserved(page) || PageKsm(page))
> continue;
> gather_stats(page, private, pte_dirty(*pte));
>
> Why did you drop a lot of check? Is it safe?

I must have been confused. For one, walk_page_range() does not even
lock the pmd entry when iterating over the pte's. I completely
overlooked that fact and so with that, the series is totally broken.

I am currently testing a slightly reworked set based on the following
variation. When finished I will send v2 of the series which will
address all issues raised so far.

Thanks again for the review!



From 013a1e0fc96f8370339209f16d81df4ded40dbf2 Mon Sep 17 00:00:00 2001
From: Stephen Wilson <wilsons@start.ca>
Date: Mon, 9 May 2011 14:39:27 -0400
Subject: [PATCH] mm: use walk_page_range() instead of custom page table
walking code

Converting show_numa_map() to use the generic routine decouples
the function from mempolicy.c, allowing it to be moved out of the mm
subsystem and into fs/proc.

Also, include KSM pages in /proc/pid/numa_maps statistics. The pagewalk
logic implemented by check_pte_range() failed to account for such pages
as they were not applicable to the page migration case.

Signed-off-by: Stephen Wilson <wilsons@start.ca>
---
mm/mempolicy.c | 75 ++++++++++++++++++++++++++++++++++++++++++++++++++-----
1 files changed, 68 insertions(+), 7 deletions(-)
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 5bfb03e..945e85d 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -2531,6 +2531,7 @@ int mpol_to_str(char *buffer, int maxlen, struct mempolicy *pol, int no_context)
}

struct numa_maps {
+ struct vm_area_struct *vma;
unsigned long pages;
unsigned long anon;
unsigned long active;
@@ -2568,6 +2569,41 @@ static void gather_stats(struct page *page, void *private, int pte_dirty)
md->node[page_to_nid(page)]++;
}

+static int gather_pte_stats(pmd_t *pmd, unsigned long addr,
+ unsigned long end, struct mm_walk *walk)
+{
+ struct numa_maps *md;
+ spinlock_t *ptl;
+ pte_t *orig_pte;
+ pte_t *pte;
+
+ md = walk->private;
+ orig_pte = pte = pte_offset_map_lock(walk->mm, pmd, addr, &ptl);
+ do {
+ struct page *page;
+ int nid;
+
+ if (!pte_present(*pte))
+ continue;
+
+ page = vm_normal_page(md->vma, addr, *pte);
+ if (!page)
+ continue;
+
+ if (PageReserved(page))
+ continue;
+
+ nid = page_to_nid(page);
+ if (!node_isset(nid, node_states[N_HIGH_MEMORY]))
+ continue;
+
+ gather_stats(page, md, pte_dirty(*pte));
+
+ } while (pte++, addr += PAGE_SIZE, addr != end);
+ pte_unmap_unlock(orig_pte, ptl);
+ return 0;
+}
+
#ifdef CONFIG_HUGETLB_PAGE
static void check_huge_range(struct vm_area_struct *vma,
unsigned long start, unsigned long end,
@@ -2597,12 +2633,35 @@ static void check_huge_range(struct vm_area_struct *vma,
gather_stats(page, md, pte_dirty(*ptep));
}
}
+
+static int gather_hugetbl_stats(pte_t *pte, unsigned long hmask,
+ unsigned long addr, unsigned long end, struct mm_walk *walk)
+{
+ struct page *page;
+
+ if (pte_none(*pte))
+ return 0;
+
+ page = pte_page(*pte);
+ if (!page)
+ return 0;
+
+ gather_stats(page, walk->private, pte_dirty(*pte));
+ return 0;
+}
+
#else
static inline void check_huge_range(struct vm_area_struct *vma,
unsigned long start, unsigned long end,
struct numa_maps *md)
{
}
+
+static int gather_hugetbl_stats(pte_t *pte, unsigned long hmask,
+ unsigned long addr, unsigned long end, struct mm_walk *walk)
+{
+ return 0;
+}
#endif

/*
@@ -2615,6 +2674,7 @@ int show_numa_map(struct seq_file *m, void *v)
struct numa_maps *md;
struct file *file = vma->vm_file;
struct mm_struct *mm = vma->vm_mm;
+ struct mm_walk walk = {};
struct mempolicy *pol;
int n;
char buffer[50];
@@ -2626,6 +2686,13 @@ int show_numa_map(struct seq_file *m, void *v)
if (!md)
return 0;

+ md->vma = vma;
+
+ walk.hugetlb_entry = gather_hugetbl_stats;
+ walk.pmd_entry = gather_pte_stats;
+ walk.private = md;
+ walk.mm = mm;
+
pol = get_vma_policy(priv->task, vma, vma->vm_start);
mpol_to_str(buffer, sizeof(buffer), pol, 0);
mpol_cond_put(pol);
@@ -2642,13 +2709,7 @@ int show_numa_map(struct seq_file *m, void *v)
seq_printf(m, " stack");
}

- if (is_vm_hugetlb_page(vma)) {
- check_huge_range(vma, vma->vm_start, vma->vm_end, md);
- seq_printf(m, " huge");
- } else {
- check_pgd_range(vma, vma->vm_start, vma->vm_end,
- &node_states[N_HIGH_MEMORY], MPOL_MF_STATS, md);
- }
+ walk_page_range(vma->vm_start, vma->vm_end, &walk);

if (!md->pages)
goto out;
--
1.7.4.4




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