page->pfmemalloc does not deserve a spot in 'struct page'. It is
only used transiently _just_ after a page leaves the buddy
allocator.
Instead of declaring a union, we move its functionality behind a
few quick accessor functions. This way we could also much more
easily audit that it is being used correctly in debugging
scenarios. For instance, we could store a magic number in there
which could never get reused as a page->index and check that the
magic number exists in page_pfmemalloc().
Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
---
linux.git-davehans/include/linux/mm.h | 17 +++++++++++++++++
linux.git-davehans/include/linux/mm_types.h | 9 ---------
linux.git-davehans/include/linux/skbuff.h | 10 +++++-----
linux.git-davehans/mm/page_alloc.c | 2 +-
linux.git-davehans/mm/slab.c | 4 ++--
linux.git-davehans/mm/slub.c | 2 +-
6 files changed, 26 insertions(+), 18 deletions(-)
diff -puN include/linux/mm.h~page_pfmemalloc-only-used-by-slab include/linux/mm.h
--- linux.git/include/linux/mm.h~page_pfmemalloc-only-used-by-slab 2013-12-13 15:51:47.467218911 -0800
+++ linux.git-davehans/include/linux/mm.h 2013-12-13 15:51:47.475219263 -0800
@@ -2013,5 +2013,22 @@ void __init setup_nr_node_ids(void);
static inline void setup_nr_node_ids(void) {}
#endif
+/*
+ * If set by the page allocator, ALLOC_NO_WATERMARKS was set and the
+ * low watermark was not met implying that the system is under some
+ * pressure. The caller should try ensure this page is only used to
+ * free other pages. Currently only used by sl[au]b. Note that
+ * this is only valid for a short time after the page returns
+ * from the allocator.
+ */
+static inline int page_pfmemalloc(struct page *page)
+{
+ return !!page->index;
+}
+static inline void set_page_pfmemalloc(struct page *page, int pfmemalloc)
+{
+ page->index = pfmemalloc;
+}
+
#endif /* __KERNEL__ */
#endif /* _LINUX_MM_H */
diff -puN include/linux/mm_types.h~page_pfmemalloc-only-used-by-slab include/linux/mm_types.h
--- linux.git/include/linux/mm_types.h~page_pfmemalloc-only-used-by-slab 2013-12-13 15:51:47.468218955 -0800
+++ linux.git-davehans/include/linux/mm_types.h 2013-12-13 15:51:47.475219263 -0800
@@ -60,15 +60,6 @@ struct page {
union {
pgoff_t index; /* Our offset within mapping. */
void *freelist; /* sl[aou]b first free object */
- bool pfmemalloc; /* If set by the page allocator,
- * ALLOC_NO_WATERMARKS was set
- * and the low watermark was not
- * met implying that the system
- * is under some pressure. The
- * caller should try ensure
- * this page is only used to
- * free other pages.
- */
};
union {
diff -puN include/linux/skbuff.h~page_pfmemalloc-only-used-by-slab include/linux/skbuff.h
--- linux.git/include/linux/skbuff.h~page_pfmemalloc-only-used-by-slab 2013-12-13 15:51:47.469218999 -0800
+++ linux.git-davehans/include/linux/skbuff.h 2013-12-13 15:51:47.475219263 -0800
@@ -1322,11 +1322,11 @@ static inline void __skb_fill_page_desc(
skb_frag_t *frag = &skb_shinfo(skb)->frags[i];
/*
- * Propagate page->pfmemalloc to the skb if we can. The problem is
+ * Propagate page_pfmemalloc() to the skb if we can. The problem is
* that not all callers have unique ownership of the page. If
* pfmemalloc is set, we check the mapping as a mapping implies
* page->index is set (index and pfmemalloc share space).
- * If it's a valid mapping, we cannot use page->pfmemalloc but we
+ * If it's a valid mapping, we cannot use page_pfmemalloc() but we
* do not lose pfmemalloc information as the pages would not be
* allocated using __GFP_MEMALLOC.
*/
@@ -1335,7 +1335,7 @@ static inline void __skb_fill_page_desc(
skb_frag_size_set(frag, size);
page = compound_head(page);
- if (page->pfmemalloc && !page->mapping)
+ if (page_pfmemalloc(page) && !page->mapping)
skb->pfmemalloc = true;
}
@@ -1917,7 +1917,7 @@ static inline struct page *__skb_alloc_p
gfp_mask |= __GFP_MEMALLOC;
page = alloc_pages_node(NUMA_NO_NODE, gfp_mask, order);
- if (skb && page && page->pfmemalloc)
+ if (skb && page && page_pfmemalloc(page))
skb->pfmemalloc = true;
return page;
@@ -1946,7 +1946,7 @@ static inline struct page *__skb_alloc_p
static inline void skb_propagate_pfmemalloc(struct page *page,
struct sk_buff *skb)
{
- if (page && page->pfmemalloc)
+ if (page && page_pfmemalloc(page))
skb->pfmemalloc = true;
}
diff -puN mm/page_alloc.c~page_pfmemalloc-only-used-by-slab mm/page_alloc.c
--- linux.git/mm/page_alloc.c~page_pfmemalloc-only-used-by-slab 2013-12-13 15:51:47.470219043 -0800
+++ linux.git-davehans/mm/page_alloc.c 2013-12-13 15:51:47.477219351 -0800
@@ -2066,7 +2066,7 @@ this_zone_full:
* memory. The caller should avoid the page being used
* for !PFMEMALLOC purposes.
*/
- page->pfmemalloc = !!(alloc_flags & ALLOC_NO_WATERMARKS);
+ set_page_pfmemalloc(page, alloc_flags & ALLOC_NO_WATERMARKS);
return page;
}
diff -puN mm/slab.c~page_pfmemalloc-only-used-by-slab mm/slab.c
--- linux.git/mm/slab.c~page_pfmemalloc-only-used-by-slab 2013-12-13 15:51:47.471219087 -0800
+++ linux.git-davehans/mm/slab.c 2013-12-13 15:51:47.478219395 -0800
@@ -1672,7 +1672,7 @@ static struct page *kmem_getpages(struct
}
/* Record if ALLOC_NO_WATERMARKS was set when allocating the slab */
- if (unlikely(page->pfmemalloc))
+ if (unlikely(page_pfmemalloc(page)))
pfmemalloc_active = true;
nr_pages = (1 << cachep->gfporder);
@@ -1683,7 +1683,7 @@ static struct page *kmem_getpages(struct
add_zone_page_state(page_zone(page),
NR_SLAB_UNRECLAIMABLE, nr_pages);
__SetPageSlab(page);
- if (page->pfmemalloc)
+ if (page_pfmemalloc(page))
SetPageSlabPfmemalloc(page);
memcg_bind_pages(cachep, cachep->gfporder);
diff -puN mm/slub.c~page_pfmemalloc-only-used-by-slab mm/slub.c
--- linux.git/mm/slub.c~page_pfmemalloc-only-used-by-slab 2013-12-13 15:51:47.472219131 -0800
+++ linux.git-davehans/mm/slub.c 2013-12-13 15:51:47.478219395 -0800
@@ -1403,7 +1403,7 @@ static struct page *new_slab(struct kmem
memcg_bind_pages(s, order);
page->slab_cache = s;
__SetPageSlab(page);
- if (page->pfmemalloc)
+ if (page_pfmemalloc(page))
SetPageSlabPfmemalloc(page);
start = page_address(page);
_
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