slab: cleanup kmem_getpages

PATCH In review Christoph Hellwig 3 participants 4 messages Apr 14, 2006 – Apr 18, 2006 Memory management

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Christoph Hellwig

author

2006-04-14 18:36 UTC #0 lore raw

PATCH 1/1 slab: cleanup kmem_getpages

The last ifdef addition hit the ugliness treshold on this functions, so:

- rename the varibale i to nr_pages so it's somewhat descriptive
- remove the addr variable and do the page_address call at the very end
- instead of ifdef'ing the whole alloc_pages_node call just make the __GFP_COMP addition to flags conditional
- rewrite the __GFP_COMP comment to make sense

Signed-off-by Christoph Hellwig <[email protected]>

mm/slab.c +13 ~~-14~~

Index: linux-2.6/mm/slab.c
===================================================================
@@ -1452,31 +1452,30 @@
 static void *kmem_getpages(struct kmem_cache *cachep, gfp_t flags, int nodeid)
 {
 	struct page *page;
-	void *addr;
-	int i;
+	int nr_pages;
 
-	flags |= cachep->gfpflags;
 #ifndef CONFIG_MMU
-	/* nommu uses slab's for process anonymous memory allocations, so
-	 * requires __GFP_COMP to properly refcount higher order allocations"
+	/*
+	 * Nommu uses slab's for process anonymous memory allocations, and thus
+	 * requires __GFP_COMP to properly refcount higher order allocations
 	 */
-	page = alloc_pages_node(nodeid, (flags | __GFP_COMP), cachep->gfporder);
-#else
-	page = alloc_pages_node(nodeid, flags, cachep->gfporder);
+	flags |= __GFP_COMP;
 #endif
+	flags |= cachep->gfpflags;
+
+	page = alloc_pages_node(nodeid, flags, cachep->gfporder);
 	if (!page)
 		return NULL;
-	addr = page_address(page);
 
-	i = (1 << cachep->gfporder);
+	nr_pages = (1 << cachep->gfporder);
 	if (cachep->flags & SLAB_RECLAIM_ACCOUNT)
-		atomic_add(i, &slab_reclaim_pages);
-	add_page_state(nr_slab, i);
-	while (i--) {
+		atomic_add(nr_pages, &slab_reclaim_pages);
+	add_page_state(nr_slab, nr_pages);
+	while (nr_pages--) {
 		__SetPageSlab(page);
 		page++;
 	}
-	return addr;
+	return page_address(page);
 }
 
 /*

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David Chinner

2006-04-18 23:20 UTC #1 lore raw

Quoted 7 lines · Christoph Hellwig

The last ifdef addition hit the ugliness treshold on this functions, so:
- rename the varibale i to nr_pages so it's somewhat descriptive
- remove the addr variable and do the page_address call at the very end
- instead of ifdef'ing the whole alloc_pages_node call just make the __GFP_COMP addition to flags conditional
- rewrite the __GFP_COMP comment to make sense

....

Quoted 4 lines

mm/slab.c +1 -1

+	page = alloc_pages_node(nodeid, flags, cachep->gfporder);
 	if (!page)
 		return NULL;
-	addr = page_address(page);

.....

mm/slab.c line 1478

Quoted 6 lines

mm/slab.c +2 -1

+	while (nr_pages--) {
 		__SetPageSlab(page);
 		page++;
 	}
-	return addr;
+	return page_address(page);

I think that's a bug - you return the address of the page after the allocation, not the first page of the allocation.

Cheers,

Dave.

Signature · 9 lines

Dave Chinner
R&D Software Enginner
SGI Australian Software Group

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Christoph Hellwig

author

2006-04-18 23:24 UTC #2 lore raw

Quoted 14 lines · David Chinner

Quoted 7 lines · Christoph Hellwig
The last ifdef addition hit the ugliness treshold on this functions, so:
- rename the varibale i to nr_pages so it's somewhat descriptive
- remove the addr variable and do the page_address call at the very end
- instead of ifdef'ing the whole alloc_pages_node call just make the __GFP_COMP addition to flags conditional
- rewrite the __GFP_COMP comment to make sense
....
Quoted 4 lines
mm/slab.c +1 -1
+	page = alloc_pages_node(nodeid, flags, cachep->gfporder);
 	if (!page)
 		return NULL;
-	addr = page_address(page);
.....

Quoted 9 lines

mm/slab.c line 1478
Quoted 6 lines
mm/slab.c +2 -1
+	while (nr_pages--) {
 		__SetPageSlab(page);
 		page++;
 	}
-	return addr;
+	return page_address(page);
I think that's a bug - you return the address of the page after the allocation, not the first page of the allocation.

You're right. I wonder why this didn't show up in my testing. Looks like slab will never allocate any high-order pages if your page size is big enough..

Andrew, please drop this for now. I'll redo it without that bit once I'll get some time.

Andrew Morton

2006-04-18 23:38 UTC #3 lore raw

Quoted 16 lines · Christoph Hellwig

Quoted 6 lines
Quoted 5 lines
(quoted diff) +1 -1
+	page = alloc_pages_node(nodeid, flags, cachep->gfporder);
 	if (!page)
 		return NULL;
-	addr = page_address(page);
.....
Quoted 9 lines
Review
Quoted 6 lines
(quoted diff) +2 -1
+	while (nr_pages--) {
 		__SetPageSlab(page);
 		page++;
 	}
-	return addr;
+	return page_address(page);
I think that's a bug - you return the address of the page after the allocation, not the first page of the allocation.

Quoted 6 lines

You're right. I wonder why this didn't show up in my testing. Looks like slab will never allocate any high-order pages if your page size is big enough..
Andrew, please drop this for now. I'll redo it without that bit once I'll get some time.

I already fixed it - it was giving me instantaneous oopses.

mm/slab.c renamed from mm/slab.c~slab-cleanup-kmem_getpages-fix +3 -4

@@ -1492,6 +1492,7 @@ static void *kmem_getpages(struct kmem_c
 {
 	struct page *page;
 	int nr_pages;
+	int i;
 
 #ifndef CONFIG_MMU
 	/*

@@ -1510,10 +1511,8 @@ static void *kmem_getpages(struct kmem_c
 	if (cachep->flags & SLAB_RECLAIM_ACCOUNT)
 		atomic_add(nr_pages, &slab_reclaim_pages);
 	add_page_state(nr_slab, nr_pages);
-	while (nr_pages--) {
-		__SetPageSlab(page);
-		page++;
-	}
+	for (i = 0; i < nr_pages; i++)
+		__SetPageSlab(page + i);
 	return page_address(page);
 }