Messages in this thread | | | Date | Fri, 9 Oct 1998 18:08:57 +0100 | From | Jamie Lokier <> | Subject | Re: 'disposable' dirty pages [was: Out Of Memory in v. 2.1] |
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On Fri, Oct 09, 1998 at 12:50:03PM -0400, Kenneth Albanowski wrote: > Yes, uniformly yucky. It feels like disappearing 4K pages could be of use > in some contexts (places where either the cached data fits easily in a 4K > page, or the data is continuous, and 4K chunks can be recalculated as > needed.) but not especially easy to use -- and also not portable. Just > move over to an Alpha, and you're working with 8K pages all of a sudden...
See my suggestion for "unmap-on-discard" pages, that would solve this in a simpler way and has other useful properties (especially the ability to reclaim unused portions of cached objects). And no need for a VMA.
> Yes, the only overhead is the extra (internal) trap to turn off the > discardable flag, and then the syscall to turn the bit back on (if you are > using the memory as a cache). That should be a miniscule overhead, though.
You don't need the internal trap -- check if a page is discardable when it's aged enough to remove it. The normal page ageing will detect "next touch", you just have to clear the touched/dirty bits when marking a page discardable.
Of course, architectures which don't have a touched bit per pte will need a trap, but they need it for page ageing anyway, it's presumably already done and implemented.
-- Jamie
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