mm: defer flush of writable TLB entries

If a PTE is unmapped and it's dirty then it was writable recently.  Due to
deferred TLB flushing, it's best to assume a writable TLB cache entry
exists.  With that assumption, the TLB must be flushed before any IO can
start or the page is freed to avoid lost writes or data corruption.  This
patch defers flushing of potentially writable TLBs as long as possible.

Signed-off-by: Mel Gorman <mgorman@suse.de>
Reviewed-by: Rik van Riel <riel@redhat.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Acked-by: Ingo Molnar <mingo@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 7 insertions, 0 deletions

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 3c602c20c717..a4ab9daa387c 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1354,6 +1354,13 @@ struct tlbflush_unmap_batch {
 
         /* True if any bit in cpumask is set */
         bool flush_required;
+
+        /*
+         * If true then the PTE was dirty when unmapped. The entry must be
+         * flushed before IO is initiated or a stale TLB entry potentially
+         * allows an update without redirtying the page.
+         */
+        bool writable;
 };
 
 struct task_struct {