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mm: combine LRU and main union in struct page

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This gives us five words of space in a single union in struct page.  The
compound_mapcount moves position (from offset 24 to offset 20) on 64-bit
systems, but that does not seem likely to cause any trouble.

Link: http://lkml.kernel.org/r/20180518194519.3820-11-willy@infradead.org
Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Jérôme Glisse <jglisse@redhat.com>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Matthew Wilcox 2018-06-07 17:08:50 -07:00 committed by Linus Torvalds
parent b7ccc7f8c6
commit 4da1984edb
2 changed files with 47 additions and 52 deletions
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95
include/linux/mm_types.h
View File

@ -73,59 +73,19 @@ struct page {
unsigned long flags; /* Atomic flags, some possibly
* updated asynchronously */
/*
* WARNING: bit 0 of the first word encode PageTail(). That means
* the rest users of the storage space MUST NOT use the bit to
* Five words (20/40 bytes) are available in this union.
* WARNING: bit 0 of the first word is used for PageTail(). That
* means the other users of this union MUST NOT use the bit to
* avoid collision and false-positive PageTail().
*/
union {
struct list_head lru; /* Pageout list, eg. active_list
* protected by zone_lru_lock !
* Can be used as a generic list
struct { /* Page cache and anonymous pages */
/**
* @lru: Pageout list, eg. active_list protected by
* zone_lru_lock. Sometimes used as a generic list
* by the page owner.
*/
struct dev_pagemap *pgmap; /* ZONE_DEVICE pages are never on an
* lru or handled by a slab
* allocator, this points to the
* hosting device page map.
*/
struct { /* slub per cpu partial pages */
struct page *next; /* Next partial slab */
#ifdef CONFIG_64BIT
int pages; /* Nr of partial slabs left */
int pobjects; /* Approximate # of objects */
#else
short int pages;
short int pobjects;
#endif
};
struct rcu_head rcu_head; /* Used by SLAB
* when destroying via RCU
*/
/* Tail pages of compound page */
struct {
unsigned long compound_head; /* If bit zero is set */
/* First tail page only */
unsigned char compound_dtor;
unsigned char compound_order;
/* two/six bytes available here */
};
#if defined(CONFIG_TRANSPARENT_HUGEPAGE) && USE_SPLIT_PMD_PTLOCKS
struct {
unsigned long __pad; /* do not overlay pmd_huge_pte
* with compound_head to avoid
* possible bit 0 collision.
*/
pgtable_t pmd_huge_pte; /* protected by page->ptl */
};
#endif
};
/* Three words (12/24 bytes) are available in this union. */
union {
struct { /* Page cache and anonymous pages */
struct list_head lru;
/* See page-flags.h for PAGE_MAPPING_FLAGS */
struct address_space *mapping;
pgoff_t index; /* Our offset within mapping. */
@ -138,6 +98,19 @@ struct page {
unsigned long private;
};
struct { /* slab, slob and slub */
union {
struct list_head slab_list; /* uses lru */
struct { /* Partial pages */
struct page *next;
#ifdef CONFIG_64BIT
int pages; /* Nr of pages left */
int pobjects; /* Approximate count */
#else
short int pages;
short int pobjects;
#endif
};
};
struct kmem_cache *slab_cache; /* not slob */
/* Double-word boundary */
void *freelist; /* first free object */
@ -151,9 +124,22 @@ struct page {
};
};
};
atomic_t compound_mapcount; /* first tail page */
struct list_head deferred_list; /* second tail page */
struct { /* Tail pages of compound page */
unsigned long compound_head; /* Bit zero is set */
/* First tail page only */
unsigned char compound_dtor;
unsigned char compound_order;
atomic_t compound_mapcount;
};
struct { /* Second tail page of compound page */
unsigned long _compound_pad_1; /* compound_head */
unsigned long _compound_pad_2;
struct list_head deferred_list;
};
struct { /* Page table pages */
unsigned long _pt_pad_1; /* compound_head */
pgtable_t pmd_huge_pte; /* protected by page->ptl */
unsigned long _pt_pad_2; /* mapping */
unsigned long _pt_pad_3;
#if ALLOC_SPLIT_PTLOCKS
@ -162,6 +148,15 @@ struct page {
spinlock_t ptl;
#endif
};
/** @rcu_head: You can use this to free a page by RCU. */
struct rcu_head rcu_head;
/**
* @pgmap: For ZONE_DEVICE pages, this points to the hosting
* device page map.
*/
struct dev_pagemap *pgmap;
};
union { /* This union is 4 bytes in size. */

2
mm/page_alloc.c
View File

@ -943,7 +943,7 @@ static int free_tail_pages_check(struct page *head_page, struct page *page)
}
switch (page - head_page) {
case 1:
/* the first tail page: ->mapping is compound_mapcount() */
/* the first tail page: ->mapping may be compound_mapcount() */
if (unlikely(compound_mapcount(page))) {
bad_page(page, "nonzero compound_mapcount", 0);
goto out;