On Tue, Sep 11, 2018 at 02:58:10PM +0300, Meelis Roos wrote: > The machines where I have PAE off are the ones that have less memory. > PAE is off just for performance reasons, not lack of PAE. PAE should be > present on all of my affected machines anyway and current distributions > seem to mostly assume 686 and PAE anyway for 32-bit systems. Right, most distributions don't even provide a non-PAE kernel for their users anymore. How big is the performance impact of using PAE over legacy paging? It shouldn't be too big because the top-level of the page-table only has 4 entries and is completly cached in the CPU. This makes %cr3 switches slower, but the page-walk itself still only needs 2 memory accesses. The page-table entries are also 8 bytes instead of 4 bytes, so that there is less locality in page-walks and probably a higher cache-miss rate. Regards, Joerg
