unimore/kernel-hacking-2024-linux-steffo
unimore/kernel-hacking-2024-linux-steffo
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mm: free up PG_slab

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Reclaim the Slab page flag by using a spare bit in PageType.  We are
perennially short of page flags for various purposes, and now that the
original SLAB allocator has been retired, SLUB does not use the
mapcount/page_type field.  This lets us remove a number of special cases
for ignoring mapcount on Slab pages.

[willy@infradead.org: update vmcoreinfo]
  Link: https://lkml.kernel.org/r/ZgGV-O8WYQ_83kxp@casper.infradead.org
Link: https://lkml.kernel.org/r/20240321142448.1645400-8-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Matthew Wilcox (Oracle) 2024-03-21 14:24:45 +00:00 committed by Andrew Morton
parent 8682a7be36
commit 46df8e73a4
5 changed files with 21 additions and 16 deletions
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21
include/linux/page-flags.h
View file

@ -109,7 +109,6 @@ enum pageflags {
PG_active,
PG_workingset,
PG_error,
PG_slab,
PG_owner_priv_1, /* Owner use. If pagecache, fs may use*/
PG_arch_1,
PG_reserved,
@ -524,7 +523,6 @@ PAGEFLAG(Active, active, PF_HEAD) __CLEARPAGEFLAG(Active, active, PF_HEAD)
TESTCLEARFLAG(Active, active, PF_HEAD)
PAGEFLAG(Workingset, workingset, PF_HEAD)
TESTCLEARFLAG(Workingset, workingset, PF_HEAD)
__PAGEFLAG(Slab, slab, PF_NO_TAIL)
PAGEFLAG(Checked, checked, PF_NO_COMPOUND) /* Used by some filesystems */
/* Xen */
@ -931,7 +929,7 @@ PAGEFLAG_FALSE(HasHWPoisoned, has_hwpoisoned)
#endif
/*
* For pages that are never mapped to userspace (and aren't PageSlab),
* For pages that are never mapped to userspace,
* page_type may be used. Because it is initialised to -1, we invert the
* sense of the bit, so __SetPageFoo *clears* the bit used for PageFoo, and
* __ClearPageFoo *sets* the bit used for PageFoo. We reserve a few high and
@ -947,6 +945,7 @@ PAGEFLAG_FALSE(HasHWPoisoned, has_hwpoisoned)
#define PG_table 0x00000200
#define PG_guard 0x00000400
#define PG_hugetlb 0x00000800
#define PG_slab 0x00001000
#define PageType(page, flag) \
((page->page_type & (PAGE_TYPE_BASE | flag)) == PAGE_TYPE_BASE)
@ -1041,6 +1040,20 @@ PAGE_TYPE_OPS(Table, table, pgtable)
*/
PAGE_TYPE_OPS(Guard, guard, guard)
FOLIO_TYPE_OPS(slab, slab)
/**
* PageSlab - Determine if the page belongs to the slab allocator
* @page: The page to test.
*
* Context: Any context.
* Return: True for slab pages, false for any other kind of page.
*/
static inline bool PageSlab(const struct page *page)
{
return folio_test_slab(page_folio(page));
}
#ifdef CONFIG_HUGETLB_PAGE
FOLIO_TYPE_OPS(hugetlb, hugetlb)
#else
@ -1121,7 +1134,7 @@ static __always_inline void __ClearPageAnonExclusive(struct page *page)
(1UL << PG_lru | 1UL << PG_locked | \
1UL << PG_private | 1UL << PG_private_2 | \
1UL << PG_writeback | 1UL << PG_reserved | \
1UL << PG_slab | 1UL << PG_active | \
1UL << PG_active | \
1UL << PG_unevictable | __PG_MLOCKED | LRU_GEN_MASK)
/*

2
include/trace/events/mmflags.h
View file

@ -107,7 +107,6 @@
DEF_PAGEFLAG_NAME(lru), \
DEF_PAGEFLAG_NAME(active), \
DEF_PAGEFLAG_NAME(workingset), \
DEF_PAGEFLAG_NAME(slab), \
DEF_PAGEFLAG_NAME(owner_priv_1), \
DEF_PAGEFLAG_NAME(arch_1), \
DEF_PAGEFLAG_NAME(reserved), \
@ -135,6 +134,7 @@ IF_HAVE_PG_ARCH_X(arch_3)
#define DEF_PAGETYPE_NAME(_name) { PG_##_name, __stringify(_name) }
#define __def_pagetype_names \
DEF_PAGETYPE_NAME(slab), \
DEF_PAGETYPE_NAME(hugetlb), \
DEF_PAGETYPE_NAME(offline), \
DEF_PAGETYPE_NAME(guard), \

3
kernel/vmcore_info.c
View file

@ -198,7 +198,8 @@ static int __init crash_save_vmcoreinfo_init(void)
VMCOREINFO_NUMBER(PG_private);
VMCOREINFO_NUMBER(PG_swapcache);
VMCOREINFO_NUMBER(PG_swapbacked);
VMCOREINFO_NUMBER(PG_slab);
#define PAGE_SLAB_MAPCOUNT_VALUE (~PG_slab)
VMCOREINFO_NUMBER(PAGE_SLAB_MAPCOUNT_VALUE);
#ifdef CONFIG_MEMORY_FAILURE
VMCOREINFO_NUMBER(PG_hwpoison);
#endif

9
mm/memory-failure.c
View file

@ -1251,7 +1251,6 @@ static int me_huge_page(struct page_state *ps, struct page *p)
#define mlock (1UL << PG_mlocked)
#define lru (1UL << PG_lru)
#define head (1UL << PG_head)
#define slab (1UL << PG_slab)
#define reserved (1UL << PG_reserved)
static struct page_state error_states[] = {
@ -1261,13 +1260,6 @@ static struct page_state error_states[] = {
* PG_buddy pages only make a small fraction of all free pages.
*/
/*
* Could in theory check if slab page is free or if we can drop
* currently unused objects without touching them. But just
* treat it as standard kernel for now.
*/
{ slab, slab, MF_MSG_SLAB, me_kernel },
{ head, head, MF_MSG_HUGE, me_huge_page },
{ sc|dirty, sc|dirty, MF_MSG_DIRTY_SWAPCACHE, me_swapcache_dirty },
@ -1294,7 +1286,6 @@ static struct page_state error_states[] = {
#undef mlock
#undef lru
#undef head
#undef slab
#undef reserved
static void update_per_node_mf_stats(unsigned long pfn,

2
mm/slab.h
View file

@ -84,8 +84,8 @@ struct slab {
};
struct rcu_head rcu_head;
};
unsigned int __unused;
unsigned int __page_type;
atomic_t __page_refcount;
#ifdef CONFIG_SLAB_OBJ_EXT
unsigned long obj_exts;