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SubjectRe: [slubllv6 02/17] slub: Do not use frozen page flag but a bit in the page counters
On Thu, 26 May 2011, Christoph Lameter wrote:

> Do not use a page flag for the frozen bit. It needs to be part
> of the state that is handled with cmpxchg_double(). So use a bit
> in the counter struct in the page struct for that purpose.
>

I don't think the new limit on the number of objects per page, 32767,
should cause a problem in practice.

> Also all page start out as frozen pages so set the bit
> when the page is allocated.
>

This comment is probably intended for the next patch in the series, which
modifies new_slab() to set the bit on allocation. There's no new behavior
introduced by this patch.

> Signed-off-by: Christoph Lameter <cl@linux.com>
>
>
> ---
> include/linux/mm_types.h | 5 +++--
> include/linux/page-flags.h | 2 --
> mm/slub.c | 12 ++++++------
> 3 files changed, 9 insertions(+), 10 deletions(-)
>
> Index: linux-2.6/include/linux/mm_types.h
> ===================================================================
> --- linux-2.6.orig/include/linux/mm_types.h 2011-05-19 13:54:29.271151992 -0500
> +++ linux-2.6/include/linux/mm_types.h 2011-05-19 13:59:28.551151643 -0500
> @@ -41,8 +41,9 @@ struct page {
> * & limit reverse map searches.
> */
> struct { /* SLUB */
> - u16 inuse;
> - u16 objects;
> + unsigned inuse:16;
> + unsigned objects:15;
> + unsigned frozen:1;
> };
> };
> union {
> Index: linux-2.6/include/linux/page-flags.h
> ===================================================================
> --- linux-2.6.orig/include/linux/page-flags.h 2011-05-19 13:54:29.281151992 -0500
> +++ linux-2.6/include/linux/page-flags.h 2011-05-19 13:59:28.551151643 -0500
> @@ -212,8 +212,6 @@ PAGEFLAG(SwapBacked, swapbacked) __CLEAR
>
> __PAGEFLAG(SlobFree, slob_free)
>
> -__PAGEFLAG(SlubFrozen, slub_frozen)
> -

The PG_slub_frozen entry in enum pageflags also needs to be removed.

> /*
> * Private page markings that may be used by the filesystem that owns the page
> * for its own purposes.
> Index: linux-2.6/mm/slub.c
> ===================================================================
> --- linux-2.6.orig/mm/slub.c 2011-05-19 13:59:24.981151647 -0500
> +++ linux-2.6/mm/slub.c 2011-05-19 13:59:28.561151643 -0500
> @@ -166,7 +166,7 @@ static inline int kmem_cache_debug(struc
>
> #define OO_SHIFT 16
> #define OO_MASK ((1 << OO_SHIFT) - 1)
> -#define MAX_OBJS_PER_PAGE 65535 /* since page.objects is u16 */
> +#define MAX_OBJS_PER_PAGE 32767 /* since page.objects is u15 */
>
> /* Internal SLUB flags */
> #define __OBJECT_POISON 0x80000000UL /* Poison object */
> @@ -1025,7 +1025,7 @@ static noinline int free_debug_processin
> }
>
> /* Special debug activities for freeing objects */
> - if (!PageSlubFrozen(page) && !page->freelist)
> + if (!page->frozen && !page->freelist)
> remove_full(s, page);
> if (s->flags & SLAB_STORE_USER)
> set_track(s, object, TRACK_FREE, addr);
> @@ -1421,7 +1421,7 @@ static inline int lock_and_freeze_slab(s
> {
> if (slab_trylock(page)) {
> __remove_partial(n, page);
> - __SetPageSlubFrozen(page);
> + page->frozen = 1;
> return 1;
> }
> return 0;
> @@ -1535,7 +1535,7 @@ static void unfreeze_slab(struct kmem_ca
> {
> struct kmem_cache_node *n = get_node(s, page_to_nid(page));
>
> - __ClearPageSlubFrozen(page);
> + page->frozen = 0;
> if (page->inuse) {
>
> if (page->freelist) {
> @@ -1866,7 +1866,7 @@ new_slab:
> flush_slab(s, c);
>
> slab_lock(page);
> - __SetPageSlubFrozen(page);
> + page->frozen = 1;
> c->node = page_to_nid(page);
> c->page = page;
> goto load_freelist;
> @@ -2048,7 +2048,7 @@ static void __slab_free(struct kmem_cach
> page->freelist = object;
> page->inuse--;
>
> - if (unlikely(PageSlubFrozen(page))) {
> + if (unlikely(page->frozen)) {
> stat(s, FREE_FROZEN);
> goto out_unlock;
> }
>
>


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