Re: [patch 4/6] mm: merge populate and nopage into fault (fixes nonlinear)

Nick Piggin
2007-03-07T08:59:47Z

On Wed, Mar 07, 2007 at 09:27:55AM +0100, Ingo Molnar wrote:
>
> * Nick Piggin <npiggin@suse.de> wrote:
>
> > Then 4,5,6 is the fault/nonlinear rewrite, take it or leave it. I
> > thought you would have liked the patches...
>
> btw., if we decide that nonlinear isnt worth the continuing maintainance
> pain, we could internally implement/emulate sys_remap_file_pages() via a
> call to mremap() and essentially deprecate it, without breaking the ABI
> - and remove all the nonlinear code. (This would split fremap areas into
> separate vmas)

Well I think it has a few possible uses outside the PAE database
workloads. UML for one seem to be interested... as much as I don't
use them, I think nonlinear mappings are kinda cool ;)

After these patches, I don't think there is too much burden. The main
thing left really is just the objrmap stuff, but that is just handled
with a minimal 'dumb' algorithm that doesn't cost much.

Then the core of it is just the file pte handling, which really doesn't
seem to be much problem.

Apart from a handful of trivial if (pte_file()) cases throughout mm/,
our maintainance burden basically now amounts to the following patch.
Even the rmap.c change looks bigger than it is because I split out
the nonlinear unmapping code from try_to_unmap_file. Not too bad, eh? :)

--

include/asm-powerpc/pgtable.h | 12 ++++
mm/Kconfig | 6 ++
mm/Makefile | 6 +-
mm/rmap.c | 101 +++++++++++++++++++++++++-----------------
4 files changed, 83 insertions(+), 42 deletions(-)

Index: linux-2.6/include/asm-powerpc/pgtable.h
===================================================================
--- linux-2.6.orig/include/asm-powerpc/pgtable.h
+++ linux-2.6/include/asm-powerpc/pgtable.h
@@ -243,7 +243,12 @@ static inline int pte_write(pte_t pte) {
static inline int pte_exec(pte_t pte) { return pte_val(pte) & _PAGE_EXEC;}
static inline int pte_dirty(pte_t pte) { return pte_val(pte) & _PAGE_DIRTY;}
static inline int pte_young(pte_t pte) { return pte_val(pte) & _PAGE_ACCESSED;}
+
+#ifdef CONFIG_NONLINEAR
static inline int pte_file(pte_t pte) { return pte_val(pte) & _PAGE_FILE;}
+#else
+static inline int pte_file(pte_t pte) { return 0; }
+#endif

static inline void pte_uncache(pte_t pte) { pte_val(pte) |= _PAGE_NO_CACHE; }
static inline void pte_cache(pte_t pte) { pte_val(pte) &= ~_PAGE_NO_CACHE; }
@@ -483,9 +488,16 @@ extern void update_mmu_cache(struct vm_a
#define __swp_entry(type, offset) ((swp_entry_t){((type)<< 1)|((offset)<<8)})
#define __pte_to_swp_entry(pte) ((swp_entry_t){pte_val(pte) >> PTE_RPN_SHIFT})
#define __swp_entry_to_pte(x) ((pte_t) { (x).val << PTE_RPN_SHIFT })
+
+#ifdef CONFIG_NONLINEAR
#define pte_to_pgoff(pte) (pte_val(pte) >> PTE_RPN_SHIFT)
#define pgoff_to_pte(off) ((pte_t) {((off) << PTE_RPN_SHIFT)|_PAGE_FILE})
#define PTE_FILE_MAX_BITS (BITS_PER_LONG - PTE_RPN_SHIFT)
+#else
+#define pte_to_pgoff(pte) ({BUG(); -1;})
+#define pgoff_to_pte(off) ({BUG(); (pte_t){-1};})
+#define PTE_FILE_MAX_BITS 0
+#endif

/*
* kern_addr_valid is intended to indicate whether an address is a valid
Index: linux-2.6/mm/Kconfig
===================================================================
--- linux-2.6.orig/mm/Kconfig
+++ linux-2.6/mm/Kconfig
@@ -142,6 +142,12 @@ config SPLIT_PTLOCK_CPUS
#
# support for page migration
#
+config NONLINEAR
+ bool "Non linear mappings"
+ def_bool y
+ help
+ Provides support for the remap_file_pages syscall.
+
config MIGRATION
bool "Page migration"
def_bool y
Index: linux-2.6/mm/Makefile
===================================================================
--- linux-2.6.orig/mm/Makefile
+++ linux-2.6/mm/Makefile
@@ -3,9 +3,8 @@
#

mmu-y := nommu.o
-mmu-$(CONFIG_MMU) := fremap.o highmem.o madvise.o memory.o mincore.o \
- mlock.o mmap.o mprotect.o mremap.o msync.o rmap.o \
- vmalloc.o
+mmu-$(CONFIG_MMU) := highmem.o madvise.o memory.o mincore.o mlock.o \
+ mmap.o mprotect.o mremap.o msync.o rmap.o vmalloc.o

obj-y := bootmem.o filemap.o mempool.o oom_kill.o fadvise.o \
page_alloc.o page-writeback.o pdflush.o \
@@ -27,5 +26,6 @@ obj-$(CONFIG_SLOB) += slob.o
obj-$(CONFIG_SLAB) += slab.o
obj-$(CONFIG_MEMORY_HOTPLUG) += memory_hotplug.o
obj-$(CONFIG_FS_XIP) += filemap_xip.o
+obj-$(CONFIG_NONLINEAR) += fremap.o
obj-$(CONFIG_MIGRATION) += migrate.o
obj-$(CONFIG_SMP) += allocpercpu.o
Index: linux-2.6/mm/rmap.c
===================================================================
--- linux-2.6.orig/mm/rmap.c
+++ linux-2.6/mm/rmap.c
@@ -756,6 +756,7 @@ out:
return ret;
}

+#ifdef CONFIG_NONLINEAR
/*
* objrmap doesn't work for nonlinear VMAs because the assumption that
* offset-into-file correlates with offset-into-virtual-addresses does not hold.
@@ -845,53 +846,18 @@ static void try_to_unmap_cluster(unsigne
pte_unmap_unlock(pte - 1, ptl);
}

-static int try_to_unmap_anon(struct page *page, int migration)
-{
- struct anon_vma *anon_vma;
- struct vm_area_struct *vma;
- int ret = SWAP_AGAIN;
-
- anon_vma = page_lock_anon_vma(page);
- if (!anon_vma)
- return ret;
-
- list_for_each_entry(vma, &anon_vma->head, anon_vma_node) {
- ret = try_to_unmap_one(page, vma, migration);
- if (ret == SWAP_FAIL || !page_mapped(page))
- break;
- }
-
- page_unlock_anon_vma(anon_vma);
- return ret;
-}
-
-/**
- * try_to_unmap_file - unmap file page using the object-based rmap method
- * @page: the page to unmap
- *
- * Find all the mappings of a page using the mapping pointer and the vma chains
- * contained in the address_space struct it points to.
- *
- * This function is only called from try_to_unmap for object-based pages.
+/*
+ * Called with page->mapping->i_mmap_lock held.
*/
-static int try_to_unmap_file(struct page *page, int migration)
+static int try_to_unmap_file_nonlinear(struct page *page, int migration)
{
struct address_space *mapping = page->mapping;
- pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
struct vm_area_struct *vma;
- struct prio_tree_iter iter;
- int ret = SWAP_AGAIN;
unsigned long cursor;
unsigned long max_nl_cursor = 0;
unsigned long max_nl_size = 0;
unsigned int mapcount;
-
- spin_lock(&mapping->i_mmap_lock);
- vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) {
- ret = try_to_unmap_one(page, vma, migration);
- if (ret == SWAP_FAIL || !page_mapped(page))
- goto out;
- }
+ int ret = SWAP_AGAIN;

if (list_empty(&mapping->i_mmap_nonlinear))
goto out;
@@ -956,6 +922,63 @@ static int try_to_unmap_file(struct page
*/
list_for_each_entry(vma, &mapping->i_mmap_nonlinear, shared.vm_set.list)
vma->vm_private_data = NULL;
+
+out:
+ return ret;
+}
+
+#else /* CONFIG_NONLINEAR */
+static int try_to_unmap_file_nonlinear(struct page *page, int migration)
+{
+ return SWAP_AGAIN;
+}
+#endif
+
+static int try_to_unmap_anon(struct page *page, int migration)
+{
+ struct anon_vma *anon_vma;
+ struct vm_area_struct *vma;
+ int ret = SWAP_AGAIN;
+
+ anon_vma = page_lock_anon_vma(page);
+ if (!anon_vma)
+ return ret;
+
+ list_for_each_entry(vma, &anon_vma->head, anon_vma_node) {
+ ret = try_to_unmap_one(page, vma, migration);
+ if (ret == SWAP_FAIL || !page_mapped(page))
+ break;
+ }
+
+ page_unlock_anon_vma(anon_vma);
+ return ret;
+}
+
+/**
+ * try_to_unmap_file - unmap file page using the object-based rmap method
+ * @page: the page to unmap
+ *
+ * Find all the mappings of a page using the mapping pointer and the vma chains
+ * contained in the address_space struct it points to.
+ *
+ * This function is only called from try_to_unmap for object-based pages.
+ */
+static int try_to_unmap_file(struct page *page, int migration)
+{
+ struct address_space *mapping = page->mapping;
+ pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
+ struct vm_area_struct *vma;
+ struct prio_tree_iter iter;
+ int ret = SWAP_AGAIN;
+
+ spin_lock(&mapping->i_mmap_lock);
+ vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) {
+ ret = try_to_unmap_one(page, vma, migration);
+ if (ret == SWAP_FAIL || !page_mapped(page))
+ goto out;
+ }
+
+ ret = try_to_unmap_file_nonlinear(page, migration);
out:
spin_unlock(&mapping->i_mmap_lock);
return ret;