Messages in this thread | | | Date | Tue, 20 Mar 2007 19:48:10 -0700 | From | "H. Peter Anvin" <> | Subject | Re: PAGE_SIZE Availability Inconsistency |
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Anton Blanchard wrote: > Hi, > >> The advantage would be that it wouldn't require a v3 for platforms for >> which MIN_PAGE_SIZE == PAGE_SIZE, which accounts for a very large >> percentage of systems. >> >> You still have to look for the darn magic in two places, so there is no >> reason for it to be different. > > The problem is if you can hit in two places then what PAGE_SIZE should > you use to size the contents of the swap header while remaining backward > compatible. > > Im leaning towards Dave suggestion of creating a clean v3 swap header. >
Changing the header format doesn't make *ANY* difference whatsoever.
You have to write two copies of the swap header, and the kernel should check for a header at MIN_PAGE_SIZE first and then at PAGE_SIZE.
If there are fields (other than position) in the v2 swap header that are dependent on PAGE_SIZE, then the copy at MIN_PAGE_SIZE should be sized using MIN_PAGE_SIZE, and the copy at PAGE_SIZE should be sized at PAGE_SIZE. It's that simple.
Creating a new format will not help that one iota, and will create gratuitous incompatiblity for the very common case of PAGE_SIZE == MIN_PAGE_SIZE.
-hpa
-hpa
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