From d02be50dba649b4246e0c1c4b7cb5d8a8d49de9a Mon Sep 17 00:00:00 2001 From: Minchan Kim Date: Wed, 15 Apr 2015 16:15:46 -0700 Subject: zsmalloc: zsmalloc documentation Create zsmalloc doc which explains design concept and stat information. Signed-off-by: Minchan Kim Cc: Juneho Choi Cc: Gunho Lee Cc: Luigi Semenzato Cc: Dan Streetman Cc: Seth Jennings Cc: Nitin Gupta Cc: Jerome Marchand Cc: Sergey Senozhatsky Cc: Joonsoo Kim Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/zsmalloc.c | 29 ----------------------------- 1 file changed, 29 deletions(-) (limited to 'mm') diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c index 461243e14d3e..1833fc9e09cb 100644 --- a/mm/zsmalloc.c +++ b/mm/zsmalloc.c @@ -12,35 +12,6 @@ */ /* - * This allocator is designed for use with zram. Thus, the allocator is - * supposed to work well under low memory conditions. In particular, it - * never attempts higher order page allocation which is very likely to - * fail under memory pressure. On the other hand, if we just use single - * (0-order) pages, it would suffer from very high fragmentation -- - * any object of size PAGE_SIZE/2 or larger would occupy an entire page. - * This was one of the major issues with its predecessor (xvmalloc). - * - * To overcome these issues, zsmalloc allocates a bunch of 0-order pages - * and links them together using various 'struct page' fields. These linked - * pages act as a single higher-order page i.e. an object can span 0-order - * page boundaries. The code refers to these linked pages as a single entity - * called zspage. - * - * For simplicity, zsmalloc can only allocate objects of size up to PAGE_SIZE - * since this satisfies the requirements of all its current users (in the - * worst case, page is incompressible and is thus stored "as-is" i.e. in - * uncompressed form). For allocation requests larger than this size, failure - * is returned (see zs_malloc). - * - * Additionally, zs_malloc() does not return a dereferenceable pointer. - * Instead, it returns an opaque handle (unsigned long) which encodes actual - * location of the allocated object. The reason for this indirection is that - * zsmalloc does not keep zspages permanently mapped since that would cause - * issues on 32-bit systems where the VA region for kernel space mappings - * is very small. So, before using the allocating memory, the object has to - * be mapped using zs_map_object() to get a usable pointer and subsequently - * unmapped using zs_unmap_object(). - * * Following is how we use various fields and flags of underlying * struct page(s) to form a zspage. * -- cgit v1.2.3