Re: [patch 4/4] mm: Clear VM_SOFTDIRTY flag inside clear_refs_write instead of clear_soft_dirty

Andrew Morton
2014-04-15T18:06:56Z

On Mon, 24 Mar 2014 16:28:42 +0400 Cyrill Gorcunov <gorcunov@openvz.org> wrote:

> The clear_refs_write is called earlier than clear_soft_dirty and it is
> more natural to clear VM_SOFTDIRTY (which belongs to VMA entry but not
> PTEs) that early instead of clearing it a way deeper inside call chain.

This patch had some significant conflicts with the pagewalk patches:

mm-hugetlbfs-fix-rmapping-for-anonymous-hugepages-with-page_pgoff.patch
mm-hugetlbfs-fix-rmapping-for-anonymous-hugepages-with-page_pgoff-v2.patch
mm-hugetlbfs-fix-rmapping-for-anonymous-hugepages-with-page_pgoff-v3.patch
mm-hugetlbfs-fix-rmapping-for-anonymous-hugepages-with-page_pgoff-v3-fix.patch
pagewalk-update-page-table-walker-core.patch
pagewalk-update-page-table-walker-core-fix-end-address-calculation-in-walk_page_range.patch
pagewalk-update-page-table-walker-core-fix-end-address-calculation-in-walk_page_range-fix.patch
pagewalk-add-walk_page_vma.patch
smaps-redefine-callback-functions-for-page-table-walker.patch
clear_refs-redefine-callback-functions-for-page-table-walker.patch
pagemap-redefine-callback-functions-for-page-table-walker.patch
pagemap-redefine-callback-functions-for-page-table-walker-fix.patch
numa_maps-redefine-callback-functions-for-page-table-walker.patch
memcg-redefine-callback-functions-for-page-table-walker.patch
arch-powerpc-mm-subpage-protc-use-walk_page_vma-instead-of-walk_page_range.patch
pagewalk-remove-argument-hmask-from-hugetlb_entry.patch
pagewalk-remove-argument-hmask-from-hugetlb_entry-fix.patch
pagewalk-remove-argument-hmask-from-hugetlb_entry-fix-fix.patch
mempolicy-apply-page-table-walker-on-queue_pages_range.patch
mm-add-pte_present-check-on-existing-hugetlb_entry-callbacks.patch
mm-pagewalkc-move-pte-null-check.patch

I resolved this by merging
mm-softdirty-clear-vm_softdirty-flag-inside-clear_refs_write-instead-of-clear_soft_dirty.patch
on top of the pagewalk patches as below - please carefully review.

I'm hoping we'll be able to get the pagewalk patches merged in 3.16-rc1
- we'll see what happens when the testing gets underway again.

From: Cyrill Gorcunov <gorcunov@openvz.org>
Subject: mm: softdirty: clear VM_SOFTDIRTY flag inside clear_refs_write() instead of clear_soft_dirty()

clear_refs_write() is called earlier than clear_soft_dirty() and it is
more natural to clear VM_SOFTDIRTY (which belongs to VMA entry but not
PTEs) that early instead of clearing it a way deeper inside call chain.

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: Pavel Emelyanov <xemul@parallels.com>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

fs/proc/task_mmu.c | 13 ++++++++-----
1 file changed, 8 insertions(+), 5 deletions(-)

diff -puN fs/proc/task_mmu.c~mm-softdirty-clear-vm_softdirty-flag-inside-clear_refs_write-instead-of-clear_soft_dirty fs/proc/task_mmu.c
--- a/fs/proc/task_mmu.c~mm-softdirty-clear-vm_softdirty-flag-inside-clear_refs_write-instead-of-clear_soft_dirty
+++ a/fs/proc/task_mmu.c
@@ -723,9 +723,6 @@ static inline void clear_soft_dirty(stru
ptent = pte_file_clear_soft_dirty(ptent);
}

- if (vma->vm_flags & VM_SOFTDIRTY)
- vma->vm_flags &= ~VM_SOFTDIRTY;
-
set_pte_at(vma->vm_mm, addr, pte, ptent);
#endif
}
@@ -762,11 +759,16 @@ static int clear_refs_test_walk(unsigned
* Writing 1 to /proc/pid/clear_refs affects all pages.
* Writing 2 to /proc/pid/clear_refs only affects anonymous pages.
* Writing 3 to /proc/pid/clear_refs only affects file mapped pages.
+ * Writing 4 to /proc/pid/clear_refs affects all pages.
*/
if (cp->type == CLEAR_REFS_ANON && vma->vm_file)
walk->skip = 1;
if (cp->type == CLEAR_REFS_MAPPED && !vma->vm_file)
walk->skip = 1;
+ if (cp->type == CLEAR_REFS_SOFT_DIRTY) {
+ if (vma->vm_flags & VM_SOFTDIRTY)
+ vma->vm_flags &= ~VM_SOFTDIRTY;
+ }
return 0;
}

@@ -795,8 +797,9 @@ static ssize_t clear_refs_write(struct f

if (type == CLEAR_REFS_SOFT_DIRTY) {
soft_dirty_cleared = true;
- pr_warn_once("The pagemap bits 55-60 has changed their meaning! "
- "See the linux/Documentation/vm/pagemap.txt for details.\n");
+ pr_warn_once("The pagemap bits 55-60 has changed their meaning!"
+ " See the linux/Documentation/vm/pagemap.txt for "
+ "details.\n");
}

task = get_proc_task(file_inode(file));
_