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authorMatthew Wilcox <mawilcox@microsoft.com>2018-06-08 03:08:15 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2018-06-08 03:34:37 +0300
commit620b4e903179d58342503fa09d9c680d93bf7db8 (patch)
treef40077235c38641c7caef1cf03289cb65328514a
parente67d4ca79aaf9d13a00d229b1b1c96b86828e8ba (diff)
downloadlinux-620b4e903179d58342503fa09d9c680d93bf7db8.tar.xz
s390: use _refcount for pgtables
Patch series "Rearrange struct page", v6. As presented at LSFMM, this patch-set rearranges struct page to give more contiguous usable space to users who have allocated a struct page for their own purposes. For a graphical view of before-and-after, see the first two tabs of https://docs.google.com/spreadsheets/d/1tvCszs_7FXrjei9_mtFiKV6nW1FLnYyvPvW-qNZhdog/edit?usp=sharing Highlights: - deferred_list now really exists in struct page instead of just a comment. - hmm_data also exists in struct page instead of being a nasty hack. - x86's PGD pages have a real pointer to the mm_struct. - VMalloc pages now have all sorts of extra information stored in them to help with debugging and tuning. - rcu_head is no longer tied to slab in case anyone else wants to free pages by RCU. - slub's counters no longer share space with _refcount. - slub's freelist+counters are now naturally dword aligned. - slub loses a parameter to a lot of functions and a sysfs file. This patch (of 17): s390 borrows the storage used for _mapcount in struct page in order to account whether the bottom or top half is being used for 2kB page tables. I want to use that for something else, so use the top byte of _refcount instead of the bottom byte of _mapcount. _refcount may temporarily be incremented by other CPUs that see a stale pointer to this page in the page cache, but each CPU can only increment it by one, and there are no systems with 2^24 CPUs today, so they will not change the upper byte of _refcount. We do have to be a little careful not to lose any of their writes (as they will subsequently decrement the counter). Link: http://lkml.kernel.org/r/20180518194519.3820-2-willy@infradead.org Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com> Acked-by: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com> Cc: Christoph Lameter <cl@linux.com> Cc: Lai Jiangshan <jiangshanlai@gmail.com> Cc: Pekka Enberg <penberg@kernel.org> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: Jérôme Glisse <jglisse@redhat.com> 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>
-rw-r--r--arch/s390/mm/pgalloc.c21
1 files changed, 12 insertions, 9 deletions
diff --git a/arch/s390/mm/pgalloc.c b/arch/s390/mm/pgalloc.c
index 562f72955956..84bd6329a88d 100644
--- a/arch/s390/mm/pgalloc.c
+++ b/arch/s390/mm/pgalloc.c
@@ -190,14 +190,15 @@ unsigned long *page_table_alloc(struct mm_struct *mm)
if (!list_empty(&mm->context.pgtable_list)) {
page = list_first_entry(&mm->context.pgtable_list,
struct page, lru);
- mask = atomic_read(&page->_mapcount);
+ mask = atomic_read(&page->_refcount) >> 24;
mask = (mask | (mask >> 4)) & 3;
if (mask != 3) {
table = (unsigned long *) page_to_phys(page);
bit = mask & 1; /* =1 -> second 2K */
if (bit)
table += PTRS_PER_PTE;
- atomic_xor_bits(&page->_mapcount, 1U << bit);
+ atomic_xor_bits(&page->_refcount,
+ 1U << (bit + 24));
list_del(&page->lru);
}
}
@@ -218,12 +219,12 @@ unsigned long *page_table_alloc(struct mm_struct *mm)
table = (unsigned long *) page_to_phys(page);
if (mm_alloc_pgste(mm)) {
/* Return 4K page table with PGSTEs */
- atomic_set(&page->_mapcount, 3);
+ atomic_xor_bits(&page->_refcount, 3 << 24);
memset64((u64 *)table, _PAGE_INVALID, PTRS_PER_PTE);
memset64((u64 *)table + PTRS_PER_PTE, 0, PTRS_PER_PTE);
} else {
/* Return the first 2K fragment of the page */
- atomic_set(&page->_mapcount, 1);
+ atomic_xor_bits(&page->_refcount, 1 << 24);
memset64((u64 *)table, _PAGE_INVALID, 2 * PTRS_PER_PTE);
spin_lock_bh(&mm->context.lock);
list_add(&page->lru, &mm->context.pgtable_list);
@@ -242,7 +243,8 @@ void page_table_free(struct mm_struct *mm, unsigned long *table)
/* Free 2K page table fragment of a 4K page */
bit = (__pa(table) & ~PAGE_MASK)/(PTRS_PER_PTE*sizeof(pte_t));
spin_lock_bh(&mm->context.lock);
- mask = atomic_xor_bits(&page->_mapcount, 1U << bit);
+ mask = atomic_xor_bits(&page->_refcount, 1U << (bit + 24));
+ mask >>= 24;
if (mask & 3)
list_add(&page->lru, &mm->context.pgtable_list);
else
@@ -253,7 +255,6 @@ void page_table_free(struct mm_struct *mm, unsigned long *table)
}
pgtable_page_dtor(page);
- atomic_set(&page->_mapcount, -1);
__free_page(page);
}
@@ -274,7 +275,8 @@ void page_table_free_rcu(struct mmu_gather *tlb, unsigned long *table,
}
bit = (__pa(table) & ~PAGE_MASK) / (PTRS_PER_PTE*sizeof(pte_t));
spin_lock_bh(&mm->context.lock);
- mask = atomic_xor_bits(&page->_mapcount, 0x11U << bit);
+ mask = atomic_xor_bits(&page->_refcount, 0x11U << (bit + 24));
+ mask >>= 24;
if (mask & 3)
list_add_tail(&page->lru, &mm->context.pgtable_list);
else
@@ -296,12 +298,13 @@ static void __tlb_remove_table(void *_table)
break;
case 1: /* lower 2K of a 4K page table */
case 2: /* higher 2K of a 4K page table */
- if (atomic_xor_bits(&page->_mapcount, mask << 4) != 0)
+ mask = atomic_xor_bits(&page->_refcount, mask << (4 + 24));
+ mask >>= 24;
+ if (mask != 0)
break;
/* fallthrough */
case 3: /* 4K page table with pgstes */
pgtable_page_dtor(page);
- atomic_set(&page->_mapcount, -1);
__free_page(page);
break;
}