From 541c237c0923f567c9c4cabb8a81635baadc713f Mon Sep 17 00:00:00 2001 From: Pavel Emelyanov Date: Wed, 3 Jul 2013 15:01:22 -0700 Subject: pagemap: prepare to reuse constant bits with page-shift In order to reuse bits from pagemap entries gracefully, we leave the entries as is but on pagemap open emit a warning in dmesg, that bits 55-60 are about to change in a couple of releases. Next, if a user issues soft-dirty clear command via the clear_refs file (it was disabled before v3.9) we assume that he's aware of the new pagemap format, note that fact and report the bits in pagemap in the new manner. The "migration strategy" looks like this then: 1. existing users are not affected -- they don't touch soft-dirty feature, thus see old bits in pagemap, but are warned and have time to fix themselves 2. those who use soft-dirty know about new pagemap format 3. some time soon we get rid of any signs of page-shift in pagemap as well as this trick with clear-soft-dirty affecting pagemap format. Signed-off-by: Pavel Emelyanov Cc: Matt Mackall Cc: Xiao Guangrong Cc: Glauber Costa Cc: Marcelo Tosatti Cc: KOSAKI Motohiro Cc: Stephen Rothwell Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- Documentation/vm/pagemap.txt | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) (limited to 'Documentation/vm') diff --git a/Documentation/vm/pagemap.txt b/Documentation/vm/pagemap.txt index 7587493c67f1..fd7c3cfddd8e 100644 --- a/Documentation/vm/pagemap.txt +++ b/Documentation/vm/pagemap.txt @@ -15,7 +15,8 @@ There are three components to pagemap: * Bits 0-54 page frame number (PFN) if present * Bits 0-4 swap type if swapped * Bits 5-54 swap offset if swapped - * Bits 55-60 page shift (page size = 1<