On Thu, 2007-02-15 at 01:38 +0100, Nick Piggin wrote:
> On Wed, Feb 14, 2007 at 03:32:04PM -0500, Lee Schermerhorn wrote:
> > On Tue, 2007-02-13 at 07:09 +0100, Nick Piggin wrote:
> > > Hi,
> > >
> > > Just tinkering around with this and got something working, so I'll see
> > > if anyone else wants to try it.
> > >
> > > Not proposing for inclusion, but I'd be interested in comments or results.
> > >
> > > Thanks,
> > > Nick
> >
> > I've included a small patch below that allow me to build and boot with
> > these patches on an HP NUMA platform. I'm still seeing an "unable to
>
> Thanks Lee. Merged.
No worries...
I've attached another patch that closes one race and fixes a context
problem [irq/preemption state] in __unreplicate_page_range(). This
makes the locking even uglier :-(.
I get further with this patch. Boot all the way up and can run fine
with page replication. However, I still get a NULL pcd in
find_get_page_readonly() when attempting a highly parallel kernel build
[16cpu/4node numa platform]. I'm still trying to track that down.
Question about locking: looks like the pcache_descriptor members are
protected by the tree_lock of the mapping, right?
Lee
======================
Additional fixes for Nick's page cache replication patch
1) recheck that page is replicated after down grading mapping tree lock.
return results of check from __replicate_pcache().
2) in __unreplicate_pcache_range(), call __unreplicate_pcache() in appropriate
context vis a vis irqs and preemption
3) report null pcd in find_get_page_readonly(). shouldn't happen?
Signed-off-by: Lee Schermerhorn <[EMAIL PROTECTED]>
mm/filemap.c | 27 +++++++++++++++++++++------
1 file changed, 21 insertions(+), 6 deletions(-)
Index: Linux/mm/filemap.c
===================================================================
--- Linux.orig/mm/filemap.c 2007-02-15 15:25:23.000000000 -0500
+++ Linux/mm/filemap.c 2007-02-15 17:42:27.000000000 -0500
@@ -669,7 +669,6 @@ static int __replicate_pcache(struct pag
struct pcache_desc *pcd;
int nid, page_node;
int writelock = 0;
- int ret = 0;
if (unlikely(PageSwapCache(page)))
goto out;
@@ -691,7 +690,7 @@ again:
lock_page(page);
if (!page->mapping) {
unlock_page(page);
- return 0;
+ goto read_lock_out; /* reacquire read lock */
}
write_lock_irq(&mapping->tree_lock);
writelock = 1;
@@ -716,15 +715,19 @@ again:
BUG_ON(radix_tree_insert(&mapping->page_tree, offset, pcd));
radix_tree_tag_set(&mapping->page_tree, offset,
PAGECACHE_TAG_REPLICATED);
- ret = 1;
out:
if (writelock) {
write_unlock_irq(&mapping->tree_lock);
unlock_page(page);
+read_lock_out:
read_lock_irq(&mapping->tree_lock);
}
- return ret;
+ /*
+ * ensure page still replicated after demoting the tree lock
+ */
+ return (radix_tree_tag_get(&mapping->page_tree, offset,
+ PAGECACHE_TAG_REPLICATED));
}
void __unreplicate_pcache(struct address_space *mapping, unsigned long offset)
@@ -813,6 +816,11 @@ retry:
replicated:
nid = numa_node_id();
pcd = radix_tree_lookup(&mapping->page_tree, offset);
+ if (!pcd) {
+ printk(KERN_DEBUG "%s NULL pcd at tagged offset\n",
+ __FUNCTION__);
+ BUG();
+ }
if (!node_isset(nid, pcd->nodes_present)) {
struct page *repl_page;
@@ -991,9 +999,16 @@ again:
struct pcache_desc *pcd = (struct pcache_desc
*)pages[i];
pages[i] = (struct page *)pcd->master->index;
}
- read_unlock(&mapping->tree_lock);
+ read_unlock(&mapping->tree_lock); /* irqs/preempt off */
for (i = 0; i < ret; i++) {
- write_lock(&mapping->tree_lock);
+ /*
+ * __unreplicate_pcache() expects tree write locked
+ * with irq/preemption disabled.
+ */
+ if (i)
+ write_lock_irq(&mapping->tree_lock);
+ else
+ write_lock(&mapping->tree_lock);
__unreplicate_pcache(mapping, (unsigned long)pages[i]);
}
read_lock_irq(&mapping->tree_lock);
-
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