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Subject[rfc patch 1/3] mm: always pass mapping in zap_details
Date
Currently, unmap_mapping_range() only fills in the address space
information in zap details when it wants to filter private COW pages
and the zapping loops need to compare page->mapping against it.

For unmapping private COW pages on truncation, we will need this
information also in the opposite case to filter shared pages.

Demux this one check_mapping member by adding an explicit mode flag
and always pass along the address space.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: Lee Schermerhorn <Lee.Schermerhorn@hp.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
---
include/linux/mm.h | 3 ++-
mm/memory.c | 11 ++++++-----
2 files changed, 8 insertions(+), 6 deletions(-)

--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -732,7 +732,8 @@ extern void user_shm_unlock(size_t, stru
*/
struct zap_details {
struct vm_area_struct *nonlinear_vma; /* Check page->index if set */
- struct address_space *check_mapping; /* Check page->mapping if set */
+ struct address_space *mapping; /* Backing address space */
+ bool keep_private; /* Do not touch private pages */
pgoff_t first_index; /* Lowest page->index to unmap */
pgoff_t last_index; /* Highest page->index to unmap */
spinlock_t *i_mmap_lock; /* For unmap_mapping_range: */
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -824,8 +824,8 @@ static unsigned long zap_pte_range(struc
* invalidate cache without truncating:
* unmap shared but keep private pages.
*/
- if (details->check_mapping &&
- details->check_mapping != page->mapping)
+ if (details->keep_private &&
+ details->mapping != page->mapping)
continue;
/*
* Each page->index must be checked when
@@ -863,7 +863,7 @@ static unsigned long zap_pte_range(struc
continue;
}
/*
- * If details->check_mapping, we leave swap entries;
+ * If details->keep_private, we leave swap entries;
* if details->nonlinear_vma, we leave file entries.
*/
if (unlikely(details))
@@ -936,7 +936,7 @@ static unsigned long unmap_page_range(st
pgd_t *pgd;
unsigned long next;

- if (details && !details->check_mapping && !details->nonlinear_vma)
+ if (details && !details->keep_private && !details->nonlinear_vma)
details = NULL;

BUG_ON(addr >= end);
@@ -2433,7 +2433,8 @@ void unmap_mapping_range(struct address_
hlen = ULONG_MAX - hba + 1;
}

- details.check_mapping = even_cows? NULL: mapping;
+ details.mapping = mapping;
+ details.keep_private = !even_cows;
details.nonlinear_vma = NULL;
details.first_index = hba;
details.last_index = hba + hlen - 1;

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