From 12c61fe9b763812adac44522100527caf534462e Mon Sep 17 00:00:00 2001 From: Joonsoo Kim Date: Tue, 15 Mar 2016 14:54:06 -0700 Subject: [PATCH] mm/slab: fix stale code comment This patchset implements a new freed object management way, that is, OBJFREELIST_SLAB. Purpose of it is to reduce memory overhead in SLAB. SLAB needs a array to manage freed objects in a slab. If there is leftover after objects are packed into a slab, we can use it as a management array, and, in this case, there is no memory waste. But, in the other cases, we need to allocate extra memory for a management array or utilize dedicated internal memory in a slab for it. Both cases causes memory waste so it's not good. With this patchset, freed object itself can be used for a management array. So, memory waste could be reduced. Detailed idea and numbers are described in last patch's commit description. Please refer it. In fact, I tested another idea implementing OBJFREELIST_SLAB with extendable linked array through another freed object. It can remove memory waste completely but it causes more computational overhead in critical lock path and it seems that overhead outweigh benefit. So, this patchset doesn't include it. I will attach prototype just for a reference. This patch (of 16): We use freelist_idx_t type for free object management whose size would be smaller than size of unsigned int. Fix it. 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 | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/slab.c b/mm/slab.c index b3eca034d0b4..23fc4b00d0ce 100644 --- a/mm/slab.c +++ b/mm/slab.c @@ -537,7 +537,7 @@ static void cache_estimate(unsigned long gfporder, size_t buffer_size, * on it. For the latter case, the memory allocated for a * slab is used for: * - * - One unsigned int for each object + * - One freelist_idx_t for each object * - Padding to respect alignment of @align * - @buffer_size bytes for each object *