On 03.09.21 03:50, Alistair Popple wrote:

On Friday, 3 September 2021 11:39:32 AM AEST Peter Xu wrote:

quoted

On Fri, Sep 03, 2021 at 10:58:53AM +1000, Alistair Popple wrote:

quoted

On Friday, 3 September 2021 6:18:19 AM AEST Peter Xu wrote:

quoted

Use the helper for the checks.  Rename "check_mapping" into "zap_mapping"
because "check_mapping" looks like a bool but in fact it stores the mapping
itself.  When it's set, we check the mapping (it must be non-NULL).  When it's
cleared we skip the check, which works like the old way.

Move the duplicated comments to the helper too.

Signed-off-by: Peter Xu <peterx@redhat.com>
---
  include/linux/mm.h | 15 ++++++++++++++-
  mm/memory.c        | 29 ++++++-----------------------
  2 files changed, 20 insertions(+), 24 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 69259229f090..81e402a5fbc9 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h

@@ -1720,10 +1720,23 @@ extern void user_shm_unlock(size_t, struct ucounts *);
   * Parameter block passed down to zap_pte_range in exceptional cases.
   */
  struct zap_details {
-	struct address_space *check_mapping;	/* Check page->mapping if set */
+	struct address_space *zap_mapping;	/* Check page->mapping if set */
  	struct page *single_page;		/* Locked page to be unmapped */
  };
  
+/*
+ * We set details->zap_mappings when we want to unmap shared but keep private
+ * pages. Return true if skip zapping this page, false otherwise.
+ */
+static inline bool
+zap_skip_check_mapping(struct zap_details *details, struct page *page)
+{
+	if (!details || !page)
+		return false;
+
+	return details->zap_mapping != page_rmapping(page);

Shouldn't this check still be
details->zap_mapping && details->zap_mapping != page_rmapping(page)?

Previously we wouldn't skip zapping pages if even_cows == true (ie.
details->check_mapping == NULL). With this change the check when
even_cows == true becomes NULL != page_rmapping(page). Doesn't this mean we
will now skip zapping any pages with a mapping when even_cows == true?

Yes I think so.  Thanks for pointing that out, Alistair, I'll fix in v3.

But frankly I really think we should simply have that flag I used to introduce.
It'll make everything much clearer.

Yeah, I think a flag would also be fine.

I still don't see the need for a flag quite frankly. Just factor out the 
checks we already have ... no change in behavior.


-- 
Thanks,

David / dhildenb