[PATCH] mm: split page table lock
Christoph Lameter demonstrated very poor scalability on the SGI 512-way, with
a many-threaded application which concurrently initializes different parts of
a large anonymous area.
This patch corrects that, by using a separate spinlock per page table page, to
guard the page table entries in that page, instead of using the mm's single
page_table_lock. (But even then, page_table_lock is still used to guard page
table allocation, and anon_vma allocation.)
In this implementation, the spinlock is tucked inside the struct page of the
page table page: with a BUILD_BUG_ON in case it overflows - which it would in
the case of 32-bit PA-RISC with spinlock debugging enabled.
Splitting the lock is not quite for free: another cacheline access. Ideally,
I suppose we would use split ptlock only for multi-threaded processes on
multi-cpu machines; but deciding that dynamically would have its own costs.
So for now enable it by config, at some number of cpus - since the Kconfig
language doesn't support inequalities, let preprocessor compare that with
NR_CPUS. But I don't think it's worth being user-configurable: for good
testing of both split and unsplit configs, split now at 4 cpus, and perhaps
change that to 8 later.
There is a benefit even for singly threaded processes: kswapd can be attacking
one part of the mm while another part is busy faulting.
Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/fs/jfs/jfs_metapage.c b/fs/jfs/jfs_metapage.c
index 26091a5..8a53981 100644
--- a/fs/jfs/jfs_metapage.c
+++ b/fs/jfs/jfs_metapage.c
@@ -86,7 +86,7 @@
atomic_t io_count;
struct metapage *mp[MPS_PER_PAGE];
};
-#define mp_anchor(page) ((struct meta_anchor *)page->private)
+#define mp_anchor(page) ((struct meta_anchor *)page_private(page))
static inline struct metapage *page_to_mp(struct page *page, uint offset)
{
@@ -108,7 +108,7 @@
if (!a)
return -ENOMEM;
memset(a, 0, sizeof(struct meta_anchor));
- page->private = (unsigned long)a;
+ set_page_private(page, (unsigned long)a);
SetPagePrivate(page);
kmap(page);
}
@@ -136,7 +136,7 @@
a->mp[index] = NULL;
if (--a->mp_count == 0) {
kfree(a);
- page->private = 0;
+ set_page_private(page, 0);
ClearPagePrivate(page);
kunmap(page);
}
@@ -156,13 +156,13 @@
#else
static inline struct metapage *page_to_mp(struct page *page, uint offset)
{
- return PagePrivate(page) ? (struct metapage *)page->private : NULL;
+ return PagePrivate(page) ? (struct metapage *)page_private(page) : NULL;
}
static inline int insert_metapage(struct page *page, struct metapage *mp)
{
if (mp) {
- page->private = (unsigned long)mp;
+ set_page_private(page, (unsigned long)mp);
SetPagePrivate(page);
kmap(page);
}
@@ -171,7 +171,7 @@
static inline void remove_metapage(struct page *page, struct metapage *mp)
{
- page->private = 0;
+ set_page_private(page, 0);
ClearPagePrivate(page);
kunmap(page);
}
