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Date: Sun, 17 May 2009 21:09:07 +0800
From: Wu Fengguang <fengguang.wu@...el.com>
To: Mel Gorman <mel@....ul.ie>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
LKML <linux-kernel@...r.kernel.org>,
Matt Mackall <mpm@...enic.com>,
KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
Andi Kleen <andi@...stfloor.org>,
"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [PATCH 1/8] mm: introduce PageHuge() for testing huge/gigantic
pages
On Thu, May 14, 2009 at 01:05:53AM +0800, Mel Gorman wrote:
> Sorry to join the game so late.
>
> On Fri, May 08, 2009 at 06:53:21PM +0800, Wu Fengguang wrote:
> > Introduce PageHuge(), which identifies huge/gigantic pages
> > by their dedicated compound destructor functions.
> >
> > Signed-off-by: Wu Fengguang <fengguang.wu@...el.com>
> > ---
> > include/linux/mm.h | 24 ++++++++++++++++++++++++
> > mm/hugetlb.c | 2 +-
> > mm/page_alloc.c | 11 ++++++++++-
> > 3 files changed, 35 insertions(+), 2 deletions(-)
> >
> > --- linux.orig/mm/page_alloc.c
> > +++ linux/mm/page_alloc.c
> > @@ -299,13 +299,22 @@ void prep_compound_page(struct page *pag
> > }
> >
> > #ifdef CONFIG_HUGETLBFS
> > +/*
> > + * This (duplicated) destructor function distinguishes gigantic pages from
> > + * normal compound pages.
> > + */
> > +void free_gigantic_page(struct page *page)
> > +{
> > + __free_pages_ok(page, compound_order(page));
> > +}
> > +
> > void prep_compound_gigantic_page(struct page *page, unsigned long order)
> > {
> > int i;
> > int nr_pages = 1 << order;
> > struct page *p = page + 1;
> >
> > - set_compound_page_dtor(page, free_compound_page);
> > + set_compound_page_dtor(page, free_gigantic_page);
> > set_compound_order(page, order);
>
> This made me raise an eyebrow. gigantic pages can never end up back in the
> page allocator. It should cause bugs all over the place so I looked closer
> and this free_gigantic_page() looks unnecessary.
>
> This is what happens for gigantic pages at boot-time
>
> gather_bootmem_prealloc() called at boot-time to gather gigantic pages
> -> Find the boot allocated pages and call prep_compound_huge_page()
> -> For gigantic pages, call prep_compound_gigantic_page(), sets destructor to free_compound_page()
> -> Call prep_new_huge_page(), sets destructor to free_huge_page()
>
> So, free_gigantic_page() should never used as such in reality and you can
> just check free_huge_page(). If a gigantic page was really freed that way,
> it would be really bad.
>
> Does that make sense?
You are right, thanks!
> > +#ifdef CONFIG_HUGETLBFS
> > +void free_huge_page(struct page *page);
> > +void free_gigantic_page(struct page *page);
> > +
> > +static inline int PageHuge(struct page *page)
> > +{
> > + compound_page_dtor *dtor;
> > +
> > + if (!PageCompound(page))
> > + return 0;
> > +
> > + page = compound_head(page);
> > + dtor = get_compound_page_dtor(page);
> > +
> > + return dtor == free_huge_page ||
> > + dtor == free_gigantic_page;
> > +}
> > +#else
> > +static inline int PageHuge(struct page *page)
> > +{
> > + return 0;
> > +}
> > +#endif
>
> That is fairly hefty function to be inline and it exports free_huge_page
> and free_gigantic_page. The latter of which is dead code and the former
> which was previously a static function.
>
> At least make PageHuge a non-inlined function contained in mm/hugetlb.c and
> expose it via mm/internal.h if possible or include/linux/hugetlb.h otherwise.
OK, moved the declaration to hugetlb.h, which will be included by fs/proc/page.c.
Andrew, will you replace the -mm patch
mm-introduce-pagehuge-for-testing-huge-gigantic-pages.patch
with this one?
---
mm: introduce PageHuge() for testing huge/gigantic pages
Introduce PageHuge(), which identifies huge/gigantic pages
by their dedicated compound destructor functions.
Also move prep_compound_gigantic_page() to hugetlb.c and
move adjust_pool_surplus() close to its caller.
CC: Mel Gorman <mel@....ul.ie>
CC: Ingo Molnar <mingo@...e.hu>
Signed-off-by: Wu Fengguang <fengguang.wu@...el.com>
---
fs/proc/page.c | 1
include/linux/hugetlb.h | 7 ++
mm/hugetlb.c | 98 ++++++++++++++++++++++++--------------
mm/internal.h | 5 -
mm/page_alloc.c | 17 ------
5 files changed, 73 insertions(+), 55 deletions(-)
--- linux.orig/mm/page_alloc.c
+++ linux/mm/page_alloc.c
@@ -298,23 +298,6 @@ void prep_compound_page(struct page *pag
}
}
-#ifdef CONFIG_HUGETLBFS
-void prep_compound_gigantic_page(struct page *page, unsigned long order)
-{
- int i;
- int nr_pages = 1 << order;
- struct page *p = page + 1;
-
- set_compound_page_dtor(page, free_compound_page);
- set_compound_order(page, order);
- __SetPageHead(page);
- for (i = 1; i < nr_pages; i++, p = mem_map_next(p, page, i)) {
- __SetPageTail(p);
- p->first_page = page;
- }
-}
-#endif
-
static int destroy_compound_page(struct page *page, unsigned long order)
{
int i;
--- linux.orig/mm/hugetlb.c
+++ linux/mm/hugetlb.c
@@ -578,41 +578,6 @@ static void free_huge_page(struct page *
hugetlb_put_quota(mapping, 1);
}
-/*
- * Increment or decrement surplus_huge_pages. Keep node-specific counters
- * balanced by operating on them in a round-robin fashion.
- * Returns 1 if an adjustment was made.
- */
-static int adjust_pool_surplus(struct hstate *h, int delta)
-{
- static int prev_nid;
- int nid = prev_nid;
- int ret = 0;
-
- VM_BUG_ON(delta != -1 && delta != 1);
- do {
- nid = next_node(nid, node_online_map);
- if (nid == MAX_NUMNODES)
- nid = first_node(node_online_map);
-
- /* To shrink on this node, there must be a surplus page */
- if (delta < 0 && !h->surplus_huge_pages_node[nid])
- continue;
- /* Surplus cannot exceed the total number of pages */
- if (delta > 0 && h->surplus_huge_pages_node[nid] >=
- h->nr_huge_pages_node[nid])
- continue;
-
- h->surplus_huge_pages += delta;
- h->surplus_huge_pages_node[nid] += delta;
- ret = 1;
- break;
- } while (nid != prev_nid);
-
- prev_nid = nid;
- return ret;
-}
-
static void prep_new_huge_page(struct hstate *h, struct page *page, int nid)
{
set_compound_page_dtor(page, free_huge_page);
@@ -623,6 +588,34 @@ static void prep_new_huge_page(struct hs
put_page(page); /* free it into the hugepage allocator */
}
+static void prep_compound_gigantic_page(struct page *page, unsigned long order)
+{
+ int i;
+ int nr_pages = 1 << order;
+ struct page *p = page + 1;
+
+ /* we rely on prep_new_huge_page to set the destructor */
+ set_compound_order(page, order);
+ __SetPageHead(page);
+ for (i = 1; i < nr_pages; i++, p = mem_map_next(p, page, i)) {
+ __SetPageTail(p);
+ p->first_page = page;
+ }
+}
+
+int PageHuge(struct page *page)
+{
+ compound_page_dtor *dtor;
+
+ if (!PageCompound(page))
+ return 0;
+
+ page = compound_head(page);
+ dtor = get_compound_page_dtor(page);
+
+ return dtor == free_huge_page;
+}
+
static struct page *alloc_fresh_huge_page_node(struct hstate *h, int nid)
{
struct page *page;
@@ -1140,6 +1133,41 @@ static inline void try_to_free_low(struc
}
#endif
+/*
+ * Increment or decrement surplus_huge_pages. Keep node-specific counters
+ * balanced by operating on them in a round-robin fashion.
+ * Returns 1 if an adjustment was made.
+ */
+static int adjust_pool_surplus(struct hstate *h, int delta)
+{
+ static int prev_nid;
+ int nid = prev_nid;
+ int ret = 0;
+
+ VM_BUG_ON(delta != -1 && delta != 1);
+ do {
+ nid = next_node(nid, node_online_map);
+ if (nid == MAX_NUMNODES)
+ nid = first_node(node_online_map);
+
+ /* To shrink on this node, there must be a surplus page */
+ if (delta < 0 && !h->surplus_huge_pages_node[nid])
+ continue;
+ /* Surplus cannot exceed the total number of pages */
+ if (delta > 0 && h->surplus_huge_pages_node[nid] >=
+ h->nr_huge_pages_node[nid])
+ continue;
+
+ h->surplus_huge_pages += delta;
+ h->surplus_huge_pages_node[nid] += delta;
+ ret = 1;
+ break;
+ } while (nid != prev_nid);
+
+ prev_nid = nid;
+ return ret;
+}
+
#define persistent_huge_pages(h) (h->nr_huge_pages - h->surplus_huge_pages)
static unsigned long set_max_huge_pages(struct hstate *h, unsigned long count)
{
--- linux.orig/mm/internal.h
+++ linux/mm/internal.h
@@ -16,9 +16,6 @@
void free_pgtables(struct mmu_gather *tlb, struct vm_area_struct *start_vma,
unsigned long floor, unsigned long ceiling);
-extern void prep_compound_page(struct page *page, unsigned long order);
-extern void prep_compound_gigantic_page(struct page *page, unsigned long order);
-
static inline void set_page_count(struct page *page, int v)
{
atomic_set(&page->_count, v);
@@ -51,6 +48,8 @@ extern void putback_lru_page(struct page
*/
extern unsigned long highest_memmap_pfn;
extern void __free_pages_bootmem(struct page *page, unsigned int order);
+extern void prep_compound_page(struct page *page, unsigned long order);
+
/*
* function for dealing with page's order in buddy system.
--- linux.orig/include/linux/hugetlb.h
+++ linux/include/linux/hugetlb.h
@@ -11,6 +11,8 @@
struct ctl_table;
+int PageHuge(struct page *page);
+
static inline int is_vm_hugetlb_page(struct vm_area_struct *vma)
{
return vma->vm_flags & VM_HUGETLB;
@@ -61,6 +63,11 @@ void hugetlb_change_protection(struct vm
#else /* !CONFIG_HUGETLB_PAGE */
+static inline int PageHuge(struct page *page)
+{
+ return 0;
+}
+
static inline int is_vm_hugetlb_page(struct vm_area_struct *vma)
{
return 0;
--- linux.orig/fs/proc/page.c
+++ linux/fs/proc/page.c
@@ -6,6 +6,7 @@
#include <linux/mmzone.h>
#include <linux/proc_fs.h>
#include <linux/seq_file.h>
+#include <linux/hugetlb.h>
#include <asm/uaccess.h>
#include "internal.h"
--
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