[PATCH 3/5] mm: msync() cleanup

Peter Zijlstra
2006-06-23T22:31:45Z

With the tracking of dirty pages properly done now, msync doesn't need to
scan the PTEs anymore to determine the dirty status.

From: Hugh Dickins <hugh@veritas.com>

In looking to do that, I made some other tidyups: can remove several
#includes, and sys_msync loop termination not quite right.

Most of those points are criticisms of the existing sys_msync, not of
your patch. In particular, the loop termination errors were introduced
in 2.6.17: I did notice this shortly before it came out, but decided I
was more likely to get it wrong myself, and make matters worse if I
tried to rush a last-minute fix in. And it's not terribly likely
to go wrong, nor disastrous if it does go wrong (may miss reporting
an unmapped area; may also fsync file of a following vma).

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>

mm/msync.c | 194 +++++++++----------------------------------------------------
1 file changed, 31 insertions(+), 163 deletions(-)

Index: 2.6-mm/mm/msync.c
===================================================================
--- 2.6-mm.orig/mm/msync.c 2006-06-22 17:59:06.000000000 +0200
+++ 2.6-mm/mm/msync.c 2006-06-23 13:28:09.000000000 +0200
@@ -7,149 +7,33 @@
/*
* The msync() system call.
*/
-#include <linux/slab.h>
-#include <linux/pagemap.h>
#include <linux/fs.h>
#include <linux/mm.h>
#include <linux/mman.h>
-#include <linux/hugetlb.h>
-#include <linux/writeback.h>
#include <linux/file.h>
#include <linux/syscalls.h>

-#include <asm/pgtable.h>
-#include <asm/tlbflush.h>
-
-static unsigned long msync_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
- unsigned long addr, unsigned long end)
-{
- pte_t *pte;
- spinlock_t *ptl;
- int progress = 0;
- unsigned long ret = 0;
-
-again:
- pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
- do {
- struct page *page;
-
- if (progress >= 64) {
- progress = 0;
- if (need_resched() || need_lockbreak(ptl))
- break;
- }
- progress++;
- if (!pte_present(*pte))
- continue;
- if (!pte_maybe_dirty(*pte))
- continue;
- page = vm_normal_page(vma, addr, *pte);
- if (!page)
- continue;
- if (ptep_clear_flush_dirty(vma, addr, pte) ||
- page_test_and_clear_dirty(page))
- ret += set_page_dirty(page);
- progress += 3;
- } while (pte++, addr += PAGE_SIZE, addr != end);
- pte_unmap_unlock(pte - 1, ptl);
- cond_resched();
- if (addr != end)
- goto again;
- return ret;
-}
-
-static inline unsigned long msync_pmd_range(struct vm_area_struct *vma,
- pud_t *pud, unsigned long addr, unsigned long end)
-{
- pmd_t *pmd;
- unsigned long next;
- unsigned long ret = 0;
-
- pmd = pmd_offset(pud, addr);
- do {
- next = pmd_addr_end(addr, end);
- if (pmd_none_or_clear_bad(pmd))
- continue;
- ret += msync_pte_range(vma, pmd, addr, next);
- } while (pmd++, addr = next, addr != end);
- return ret;
-}
-
-static inline unsigned long msync_pud_range(struct vm_area_struct *vma,
- pgd_t *pgd, unsigned long addr, unsigned long end)
-{
- pud_t *pud;
- unsigned long next;
- unsigned long ret = 0;
-
- pud = pud_offset(pgd, addr);
- do {
- next = pud_addr_end(addr, end);
- if (pud_none_or_clear_bad(pud))
- continue;
- ret += msync_pmd_range(vma, pud, addr, next);
- } while (pud++, addr = next, addr != end);
- return ret;
-}
-
-static unsigned long msync_page_range(struct vm_area_struct *vma,
- unsigned long addr, unsigned long end)
-{
- pgd_t *pgd;
- unsigned long next;
- unsigned long ret = 0;
-
- /* For hugepages we can't go walking the page table normally,
- * but that's ok, hugetlbfs is memory based, so we don't need
- * to do anything more on an msync().
- */
- if (vma->vm_flags & VM_HUGETLB)
- return 0;
-
- BUG_ON(addr >= end);
- pgd = pgd_offset(vma->vm_mm, addr);
- flush_cache_range(vma, addr, end);
- do {
- next = pgd_addr_end(addr, end);
- if (pgd_none_or_clear_bad(pgd))
- continue;
- ret += msync_pud_range(vma, pgd, addr, next);
- } while (pgd++, addr = next, addr != end);
- return ret;
-}
-
/*
* MS_SYNC syncs the entire file - including mappings.
*
- * MS_ASYNC does not start I/O (it used to, up to 2.5.67). Instead, it just
- * marks the relevant pages dirty. The application may now run fsync() to
+ * MS_ASYNC does not start I/O (it used to, up to 2.5.67).
+ * Nor does it marks the relevant pages dirty (it used to up to 2.6.17).
+ * Now it doesn't do anything, since dirty pages are properly tracked.
+ *
+ * The application may now run fsync() to
* write out the dirty pages and wait on the writeout and check the result.
* Or the application may run fadvise(FADV_DONTNEED) against the fd to start
* async writeout immediately.
* So by _not_ starting I/O in MS_ASYNC we provide complete flexibility to
* applications.
*/
-static int msync_interval(struct vm_area_struct *vma, unsigned long addr,
- unsigned long end, int flags,
- unsigned long *nr_pages_dirtied)
-{
- struct file *file = vma->vm_file;
-
- if ((flags & MS_INVALIDATE) && (vma->vm_flags & VM_LOCKED))
- return -EBUSY;
-
- if (file && (vma->vm_flags & VM_SHARED))
- *nr_pages_dirtied = msync_page_range(vma, addr, end);
- return 0;
-}
-
asmlinkage long sys_msync(unsigned long start, size_t len, int flags)
{
unsigned long end;
+ struct mm_struct *mm = current->mm;
struct vm_area_struct *vma;
int unmapped_error = 0;
int error = -EINVAL;
- int done = 0;

if (flags & ~(MS_ASYNC | MS_INVALIDATE | MS_SYNC))
goto out;
@@ -169,64 +53,48 @@ asmlinkage long sys_msync(unsigned long
* If the interval [start,end) covers some unmapped address ranges,
* just ignore them, but return -ENOMEM at the end.
*/
- down_read(&current->mm->mmap_sem);
- vma = find_vma(current->mm, start);
- if (!vma) {
- error = -ENOMEM;
- goto out_unlock;
- }
- do {
- unsigned long nr_pages_dirtied = 0;
+ down_read(&mm->mmap_sem);
+ vma = find_vma(mm, start);
+ for (;;) {
struct file *file;

+ /* Still start < end. */
+ error = -ENOMEM;
+ if (!vma)
+ goto out_unlock;
/* Here start < vma->vm_end. */
if (start < vma->vm_start) {
- unmapped_error = -ENOMEM;
start = vma->vm_start;
+ if (start >= end)
+ goto out_unlock;
+ unmapped_error = -ENOMEM;
}
/* Here vma->vm_start <= start < vma->vm_end. */
- if (end <= vma->vm_end) {
- if (start < end) {
- error = msync_interval(vma, start, end, flags,
- &nr_pages_dirtied);
- if (error)
- goto out_unlock;
- }
- error = unmapped_error;
- done = 1;
- } else {
- /* Here vma->vm_start <= start < vma->vm_end < end. */
- error = msync_interval(vma, start, vma->vm_end, flags,
- &nr_pages_dirtied);
- if (error)
- goto out_unlock;
+ if ((flags & MS_INVALIDATE) &&
+ (vma->vm_flags & VM_LOCKED)) {
+ error = -EBUSY;
+ goto out_unlock;
}
file = vma->vm_file;
start = vma->vm_end;
- if ((flags & MS_ASYNC) && file && nr_pages_dirtied) {
- get_file(file);
- up_read(&current->mm->mmap_sem);
- balance_dirty_pages_ratelimited_nr(file->f_mapping,
- nr_pages_dirtied);
- fput(file);
- down_read(&current->mm->mmap_sem);
- vma = find_vma(current->mm, start);
- } else if ((flags & MS_SYNC) && file &&
+ if ((flags & MS_SYNC) && file &&
(vma->vm_flags & VM_SHARED)) {
get_file(file);
- up_read(&current->mm->mmap_sem);
+ up_read(&mm->mmap_sem);
error = do_fsync(file, 0);
fput(file);
- down_read(&current->mm->mmap_sem);
- if (error)
- goto out_unlock;
- vma = find_vma(current->mm, start);
+ if (error || start >= end)
+ goto out;
+ down_read(&mm->mmap_sem);
+ vma = find_vma(mm, start);
} else {
+ if (start >= end)
+ goto out_unlock;
vma = vma->vm_next;
}
- } while (vma && !done);
+ }
out_unlock:
- up_read(&current->mm->mmap_sem);
+ up_read(&mm->mmap_sem);
out:
- return error;
+ return error ? : unmapped_error;
}