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| author | Pavel Emelyanov <xemul@parallels.com> | 2013-07-03 15:01:22 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2013-07-03 16:07:26 -0700 |
| commit | 541c237c0923f567c9c4cabb8a81635baadc713f (patch) | |
| tree | 5f544cd43acff9e09c6f126f678e2d7c89920bbf /Documentation/vm | |
| parent | 0f8975ec4db2c8b5bd111b211292ca9be0feb6b8 (diff) | |
| download | linux-541c237c0923f567c9c4cabb8a81635baadc713f.tar.bz2 | |
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 <xemul@parallels.com>
Cc: Matt Mackall <mpm@selenic.com>
Cc: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Cc: Glauber Costa <glommer@parallels.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@gmail.com>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'Documentation/vm')
| -rw-r--r-- | Documentation/vm/pagemap.txt | 3 |
1 files changed, 2 insertions, 1 deletions
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<<page shift) + * Bit 55 pte is soft-dirty (see Documentation/vm/soft-dirty.txt) + * Bits 56-60 zero * Bit 61 page is file-page or shared-anon * Bit 62 page swapped * Bit 63 page present |