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Subject[PATCH] rmaplock 6/6 swapoff use anon_vma
Swapoff can make good use of a page's anon_vma and index, while it's
still left in swapcache, or once it's brought back in and the first pte
mapped back: unuse_vma go directly to just one page of only those vmas
with the same anon_vma. And unuse_process can skip any vmas without an
anon_vma (extending the hugetlb check: hugetlb vmas have no anon_vma).

This just hacks in on top of the existing procedure, still going through
all the vmas of all the mms in mmlist. A more elegant procedure might
replace mmlist by a list of anon_vmas: but that would be more work to
implement, with apparently more overhead in the common paths.

Signed-off-by: Hugh Dickins <hugh@veritas.com>

include/linux/rmap.h | 5 +++++
mm/rmap.c | 20 ++++++++++++++++++++
mm/swapfile.c | 23 ++++++++++++++++-------
3 files changed, 41 insertions(+), 7 deletions(-)
--- rmaplock5/include/linux/rmap.h 2004-07-12 18:20:22.333796048 +0100
+++ rmaplock6/include/linux/rmap.h 2004-07-12 18:21:16.752523144 +0100
@@ -91,6 +91,11 @@ static inline void page_dup_rmap(struct
int page_referenced(struct page *, int is_locked);
int try_to_unmap(struct page *);

+/*
+ * Used by swapoff to help locate where page is expected in vma.
+ */
+unsigned long page_address_in_vma(struct page *, struct vm_area_struct *);
+
#else /* !CONFIG_MMU */

#define anon_vma_init() do {} while (0)
--- rmaplock5/mm/rmap.c 2004-07-12 18:21:02.456696440 +0100
+++ rmaplock6/mm/rmap.c 2004-07-12 18:21:16.767520864 +0100
@@ -231,6 +231,24 @@ vma_address(struct page *page, struct vm
}

/*
+ * At what user virtual address is page expected in vma? checking that the
+ * page matches the vma: currently only used by unuse_process, on anon pages.
+ */
+unsigned long page_address_in_vma(struct page *page, struct vm_area_struct *vma)
+{
+ if (PageAnon(page)) {
+ if ((void *)vma->anon_vma !=
+ (void *)page->mapping - PAGE_MAPPING_ANON)
+ return -EFAULT;
+ } else if (page->mapping && !(vma->vm_flags & VM_NONLINEAR)) {
+ if (vma->vm_file->f_mapping != page->mapping)
+ return -EFAULT;
+ } else
+ return -EFAULT;
+ return vma_address(page, vma);
+}
+
+/*
* Subfunctions of page_referenced: page_referenced_one called
* repeatedly from either page_referenced_anon or page_referenced_file.
*/
@@ -457,6 +475,8 @@ void page_remove_rmap(struct page *page)
* which increments mapcount after us but sets mapping
* before us: so leave the reset to free_hot_cold_page,
* and remember that it's only reliable while mapped.
+ * Leaving it set also helps swapoff to reinstate ptes
+ * faster for those pages still in swapcache.
*/
if (page_test_and_clear_dirty(page))
set_page_dirty(page);
--- rmaplock5/mm/swapfile.c 2004-07-12 18:21:02.458696136 +0100
+++ rmaplock6/mm/swapfile.c 2004-07-12 18:21:16.769520560 +0100
@@ -520,14 +520,24 @@ static unsigned long unuse_pgd(struct vm
}

/* vma->vm_mm->page_table_lock is held */
-static unsigned long unuse_vma(struct vm_area_struct * vma, pgd_t *pgdir,
+static unsigned long unuse_vma(struct vm_area_struct * vma,
swp_entry_t entry, struct page *page)
{
- unsigned long start = vma->vm_start, end = vma->vm_end;
+ pgd_t *pgdir;
+ unsigned long start, end;
unsigned long foundaddr;

- if (start >= end)
- BUG();
+ if (page->mapping) {
+ start = page_address_in_vma(page, vma);
+ if (start == -EFAULT)
+ return 0;
+ else
+ end = start + PAGE_SIZE;
+ } else {
+ start = vma->vm_start;
+ end = vma->vm_end;
+ }
+ pgdir = pgd_offset(vma->vm_mm, start);
do {
foundaddr = unuse_pgd(vma, pgdir, start, end - start,
entry, page);
@@ -559,9 +569,8 @@ static int unuse_process(struct mm_struc
}
spin_lock(&mm->page_table_lock);
for (vma = mm->mmap; vma; vma = vma->vm_next) {
- if (!is_vm_hugetlb_page(vma)) {
- pgd_t * pgd = pgd_offset(mm, vma->vm_start);
- foundaddr = unuse_vma(vma, pgd, entry, page);
+ if (vma->anon_vma) {
+ foundaddr = unuse_vma(vma, entry, page);
if (foundaddr)
break;
}
-
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