tree 09a3654980209397683cc7d4d8b1b3b56a9ea904
parent 130e8e09e2675bbc484581825fe29e2e5a6b8b0a
author Tobin C. Harding <tobin@kernel.org> 1557792966 -0700
committer Linus Torvalds <torvalds@linux-foundation.org> 1557852464 -0700

slob: use slab_list instead of lru

Currently we use the page->lru list for maintaining lists of slabs.  We
have a list_head in the page structure (slab_list) that can be used for
this purpose.  Doing so makes the code cleaner since we are not
overloading the lru list.

The slab_list is part of a union within the page struct (included here
stripped down):

	union {
		struct {	/* Page cache and anonymous pages */
			struct list_head lru;
			...
		};
		struct {
			dma_addr_t dma_addr;
		};
		struct {	/* slab, slob and slub */
			union {
				struct list_head slab_list;
				struct {	/* Partial pages */
					struct page *next;
					int pages;	/* Nr of pages left */
					int pobjects;	/* Approximate count */
				};
			};
		...

Here we see that slab_list and lru are the same bits.  We can verify that
this change is safe to do by examining the object file produced from
slob.c before and after this patch is applied.

Steps taken to verify:

 1. checkout current tip of Linus' tree

    commit a667cb7a94d4 ("Merge branch 'akpm' (patches from Andrew)")

 2. configure and build (select SLOB allocator)

    CONFIG_SLOB=y
    CONFIG_SLAB_MERGE_DEFAULT=y

 3. dissasemble object file `objdump -dr mm/slub.o > before.s
 4. apply patch
 5. build
 6. dissasemble object file `objdump -dr mm/slub.o > after.s
 7. diff before.s after.s

Use slab_list list_head instead of the lru list_head for maintaining
lists of slabs.

Link: http://lkml.kernel.org/r/20190402230545.2929-4-tobin@kernel.org
Signed-off-by: Tobin C. Harding <tobin@kernel.org>
Reviewed-by: Roman Gushchin <guro@fb.com>
Acked-by: Christoph Lameter <cl@linux.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Pekka Enberg <penberg@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>