On Sat, Feb 16, 2008 at 05:51:38AM -0600, Robin Holt wrote: > I am doing this in xpmem with a stack-based structure in the function > calling get_user_pages. That structure describes the start and > end address of the range we are doing the get_user_pages on. If an > invalidate_range_begin comes in while we are off to the kernel doing > the get_user_pages, the invalidate_range_begin marks that structure > indicating an invalidate came in. When the get_user_pages gets the > structures relocked, it checks that flag (really a generation counter) > and if it is set, retries the get_user_pages. After 3 retries, it > returns -EAGAIN and the fault is started over from the remote side.
A seqlock sounds a good optimization for the non-swapping fast path, a per-VM-guest seqlock number can allow us to know when we need to worry to call get_user_pages a second time, but won't be really a retry like in 99% of seqlock usages for the reader side, but just a second get_user_pages to trigger a minor fault. Then if the page is different in the second run, we'll really retry (so not in function of the seqlock but in function of the get_user_pages page array), and there's no risk of livelocks because get_user_pages returning a different page won't be the common case. The seqlock should be increased first before the invalidate and a second time once the invalidate is over. ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ _______________________________________________ kvm-devel mailing list kvm-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/kvm-devel
