[PATCH] mm: mincore anon

Make mincore work for anon mappings, nonlinear, and migration entries.
Based on patch from Linus Torvalds <torvalds@linux-foundation.org>.

Signed-off-by: Nick Piggin <npiggin@suse.de>
Acked-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 76 insertions, 26 deletions

diff --git a/mm/mincore.c b/mm/mincore.c
index 8aca6f7167bb..95c5f49f0a1a 100644
--- a/mm/mincore.c
+++ b/mm/mincore.c
@@ -12,6 +12,8 @@
 #include <linux/mm.h>
 #include <linux/mman.h>
 #include <linux/syscalls.h>
+#include <linux/swap.h>
+#include <linux/swapops.h>
 
 #include <asm/uaccess.h>
 #include <asm/pgtable.h>
@@ -22,14 +24,22 @@
  * and is up to date; i.e. that no page-in operation would be required
  * at this time if an application were to map and access this page.
  */
-static unsigned char mincore_page(struct vm_area_struct * vma,
-        unsigned long pgoff)
+static unsigned char mincore_page(struct address_space *mapping, pgoff_t pgoff)
 {
         unsigned char present = 0;
-        struct address_space * as = vma->vm_file->f_mapping;
-        struct page * page;
+        struct page *page;
 
-        page = find_get_page(as, pgoff);
+        /*
+         * When tmpfs swaps out a page from a file, any process mapping that
+         * file will not get a swp_entry_t in its pte, but rather it is like
+         * any other file mapping (ie. marked !present and faulted in with
+         * tmpfs's .nopage). So swapped out tmpfs mappings are tested here.
+         *
+         * However when tmpfs moves the page from pagecache and into swapcache,
+         * it is still in core, but the find_get_page below won't find it.
+         * No big deal, but make a note of it.
+         */
+        page = find_get_page(mapping, pgoff);
         if (page) {
                 present = PageUptodate(page);
                 page_cache_release(page);
@@ -45,7 +55,14 @@ static unsigned char mincore_page(struct vm_area_struct * vma,
  */
 static long do_mincore(unsigned long addr, unsigned char *vec, unsigned long pages)
 {
-        unsigned long i, nr, pgoff;
+        pgd_t *pgd;
+        pud_t *pud;
+        pmd_t *pmd;
+        pte_t *ptep;
+        spinlock_t *ptl;
+        unsigned long nr;
+        int i;
+        pgoff_t pgoff;
         struct vm_area_struct *vma = find_vma(current->mm, addr);
 
         /*
@@ -56,31 +73,64 @@ static long do_mincore(unsigned long addr, unsigned char *vec, unsigned long pag
                 return -ENOMEM;
 
         /*
-         * Ok, got it. But check whether it's a segment we support
-         * mincore() on. Right now, we don't do any anonymous mappings.
-         *
-         * FIXME: This is just stupid. And returning ENOMEM is 
-         * stupid too. We should just look at the page tables. But
-         * this is what we've traditionally done, so we'll just
-         * continue doing it.
+         * Calculate how many pages there are left in the last level of the
+         * PTE array for our address.
          */
-        if (!vma->vm_file)
-                return -ENOMEM;
-
-        /*
-         * Calculate how many pages there are left in the vma, and
-         * what the pgoff is for our address.
-         */
-        nr = (vma->vm_end - addr) >> PAGE_SHIFT;
+        nr = PTRS_PER_PTE - ((addr >> PAGE_SHIFT) & (PTRS_PER_PTE-1));
         if (nr > pages)
                 nr = pages;
 
-        pgoff = (addr - vma->vm_start) >> PAGE_SHIFT;
-        pgoff += vma->vm_pgoff;
+        pgd = pgd_offset(vma->vm_mm, addr);
+        if (pgd_none_or_clear_bad(pgd))
+                goto none_mapped;
+        pud = pud_offset(pgd, addr);
+        if (pud_none_or_clear_bad(pud))
+                goto none_mapped;
+        pmd = pmd_offset(pud, addr);
+        if (pmd_none_or_clear_bad(pmd))
+                goto none_mapped;
+
+        ptep = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
+        for (i = 0; i < nr; i++, ptep++, addr += PAGE_SIZE) {
+                unsigned char present;
+                pte_t pte = *ptep;
+
+                if (pte_present(pte)) {
+                        present = 1;
+
+                } else if (pte_none(pte)) {
+                        if (vma->vm_file) {
+                                pgoff = linear_page_index(vma, addr);
+                                present = mincore_page(vma->vm_file->f_mapping,
+                                                        pgoff);
+                        } else
+                                present = 0;
+
+                } else if (pte_file(pte)) {
+                        pgoff = pte_to_pgoff(pte);
+                        present = mincore_page(vma->vm_file->f_mapping, pgoff);
+
+                } else { /* pte is a swap entry */
+                        swp_entry_t entry = pte_to_swp_entry(pte);
+                        if (is_migration_entry(entry)) {
+                                /* migration entries are always uptodate */
+                                present = 1;
+                        } else {
+                                pgoff = entry.val;
+                                present = mincore_page(&swapper_space, pgoff);
+                        }
+                }
+        }
+        pte_unmap_unlock(ptep-1, ptl);
+
+        return nr;
 
-        /* And then we just fill the sucker in.. */
-        for (i = 0 ; i < nr; i++, pgoff++)
-                vec[i] = mincore_page(vma, pgoff);
+none_mapped:
+        if (vma->vm_file) {
+                pgoff = linear_page_index(vma, addr);
+                for (i = 0; i < nr; i++, pgoff++)
+                        vec[i] = mincore_page(vma->vm_file->f_mapping, pgoff);
+        }
 
         return nr;
 }