The patch titled
Subject: s390: use _refcount for pgtables
has been added to the -mm tree. Its filename is
s390-use-_refcount-for-pgtables.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/s390-use-_refcount-for-pgtables.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/s390-use-_refcount-for-pgtables.patch
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------------------------------------------------------
From: Matthew Wilcox <mawilcox@xxxxxxxxxxxxx>
Subject: 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@xxxxxxxxxxxxx
Signed-off-by: Matthew Wilcox <mawilcox@xxxxxxxxxxxxx>
Acked-by: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>
Cc: "Kirill A . Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxx>
Cc: Lai Jiangshan <jiangshanlai@xxxxxxxxx>
Cc: Pekka Enberg <penberg@xxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Jérôme Glisse <jglisse@xxxxxxxxxx>
Cc: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
arch/s390/mm/pgalloc.c | 21 ++++++++++++---------
1 file changed, 12 insertions(+), 9 deletions(-)
diff -puN arch/s390/mm/pgalloc.c~s390-use-_refcount-for-pgtables arch/s390/mm/pgalloc.c
--- a/arch/s390/mm/pgalloc.c~s390-use-_refcount-for-pgtables
+++ a/arch/s390/mm/pgalloc.c
@@ -190,14 +190,15 @@ unsigned long *page_table_alloc(struct m
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 m
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 *m
/* 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 *m
}
pgtable_page_dtor(page);
- atomic_set(&page->_mapcount, -1);
__free_page(page);
}
@@ -274,7 +275,8 @@ void page_table_free_rcu(struct mmu_gath
}
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 *_ta
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;
}
_
Patches currently in -mm which might be from mawilcox@xxxxxxxxxxxxx are
lib-test_bitmapc-fix-bitmap-optimisation-tests-to-report-errors-correctly.patch
slab-__gfp_zero-is-incompatible-with-a-constructor.patch
s390-use-_refcount-for-pgtables.patch
mm-split-page_type-out-from-_mapcount.patch
mm-mark-pages-in-use-for-page-tables.patch
mm-switch-s_mem-and-slab_cache-in-struct-page.patch
mm-move-private-union-within-struct-page.patch
mm-move-_refcount-out-of-struct-page-union.patch
mm-combine-first-three-unions-in-struct-page.patch
mm-use-page-deferred_list.patch
mm-move-lru-union-within-struct-page.patch
mm-combine-lru-and-main-union-in-struct-page.patch
mm-improve-struct-page-documentation.patch
mm-add-pt_mm-to-struct-page.patch
mm-add-hmm_data-to-struct-page.patch
slabslub-remove-rcu_head-size-checks.patch
slub-remove-kmem_cache-reserved.patch
slub-remove-reserved-file-from-sysfs.patch
mm-distinguish-vmalloc-pages.patch
ida-remove-simple_ida_lock.patch
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