From 3217fd9bdf0017bd0847939f67d52a9c71d8fc56 Mon Sep 17 00:00:00 2001 From: Joonsoo Kim Date: Tue, 15 Mar 2016 14:54:41 -0700 Subject: mm/slab: make criteria for off slab determination robust and simple To become an off slab, there are some constraints to avoid bootstrapping problem and recursive call. This can be avoided differently by simply checking that corresponding kmalloc cache is ready and it's not a off slab. It would be more robust because static size checking can be affected by cache size change or architecture type but dynamic checking isn't. One check 'freelist_cache->size > cachep->size / 2' is added to check benefit of choosing off slab, because, now, there is no size constraint which ensures enough advantage when selecting off slab. Signed-off-by: Joonsoo Kim Cc: Christoph Lameter Cc: Pekka Enberg Cc: David Rientjes Cc: Joonsoo Kim Cc: Jesper Dangaard Brouer Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/slab.c | 45 +++++++++++++++++---------------------------- 1 file changed, 17 insertions(+), 28 deletions(-) (limited to 'mm') diff --git a/mm/slab.c b/mm/slab.c index 21aad9d518a7..ab43d9fcdb81 100644 --- a/mm/slab.c +++ b/mm/slab.c @@ -272,7 +272,6 @@ static void kmem_cache_node_init(struct kmem_cache_node *parent) #define CFLGS_OFF_SLAB (0x80000000UL) #define OFF_SLAB(x) ((x)->flags & CFLGS_OFF_SLAB) -#define OFF_SLAB_MIN_SIZE (max_t(size_t, PAGE_SIZE >> 5, KMALLOC_MIN_SIZE + 1)) #define BATCHREFILL_LIMIT 16 /* @@ -1879,7 +1878,6 @@ static void slabs_destroy(struct kmem_cache *cachep, struct list_head *list) static size_t calculate_slab_order(struct kmem_cache *cachep, size_t size, unsigned long flags) { - unsigned long offslab_limit; size_t left_over = 0; int gfporder; @@ -1896,16 +1894,24 @@ static size_t calculate_slab_order(struct kmem_cache *cachep, break; if (flags & CFLGS_OFF_SLAB) { + struct kmem_cache *freelist_cache; + size_t freelist_size; + + freelist_size = num * sizeof(freelist_idx_t); + freelist_cache = kmalloc_slab(freelist_size, 0u); + if (!freelist_cache) + continue; + /* - * Max number of objs-per-slab for caches which - * use off-slab slabs. Needed to avoid a possible - * looping condition in cache_grow(). + * Needed to avoid possible looping condition + * in cache_grow() */ - offslab_limit = size; - offslab_limit /= sizeof(freelist_idx_t); + if (OFF_SLAB(freelist_cache)) + continue; - if (num > offslab_limit) - break; + /* check if off slab has enough benefit */ + if (freelist_cache->size > cachep->size / 2) + continue; } /* Found something acceptable - save it away */ @@ -2031,17 +2037,9 @@ static bool set_off_slab_cache(struct kmem_cache *cachep, cachep->num = 0; /* - * Determine if the slab management is 'on' or 'off' slab. - * (bootstrapping cannot cope with offslab caches so don't do - * it too early on. Always use on-slab management when - * SLAB_NOLEAKTRACE to avoid recursive calls into kmemleak) + * Always use on-slab management when SLAB_NOLEAKTRACE + * to avoid recursive calls into kmemleak. */ - if (size < OFF_SLAB_MIN_SIZE) - return false; - - if (slab_early_init) - return false; - if (flags & SLAB_NOLEAKTRACE) return false; @@ -2205,7 +2203,6 @@ __kmem_cache_create (struct kmem_cache *cachep, unsigned long flags) * sized slab is initialized in current slab initialization sequence. */ if (debug_pagealloc_enabled() && (flags & SLAB_POISON) && - !slab_early_init && size >= kmalloc_size(INDEX_NODE) && size >= 256 && cachep->object_size > cache_line_size()) { if (size < PAGE_SIZE || size % PAGE_SIZE == 0) { size_t tmp_size = ALIGN(size, PAGE_SIZE); @@ -2254,14 +2251,6 @@ done: if (OFF_SLAB(cachep)) { cachep->freelist_cache = kmalloc_slab(cachep->freelist_size, 0u); - /* - * This is a possibility for one of the kmalloc_{dma,}_caches. - * But since we go off slab only for object size greater than - * OFF_SLAB_MIN_SIZE, and kmalloc_{dma,}_caches get created - * in ascending order,this should not happen at all. - * But leave a BUG_ON for some lucky dude. - */ - BUG_ON(ZERO_OR_NULL_PTR(cachep->freelist_cache)); } err = setup_cpu_cache(cachep, gfp); -- cgit v1.2.3