Messages in this thread | | | From | Daniel Phillips <> | Subject | Re: Virtual address space exhaustion (was Discontigmem virt_to_page() ) | Date | Fri, 3 May 2002 18:02:18 +0200 |
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On Friday 03 May 2002 17:17, Martin J. Bligh wrote: > Andrea apparently wrote: > > Ah, and of course you could also use 2M pagetables by default to make it > > more usable but still you would run in some huge ram wastage in certain > > usages with small files, huge pageins and reads swapout and swapins, > > plus it wouldn't be guaranteed to be transparent to the userspace > > binaries (for istance mmap offset fields would break backwards > > compatibility on the required alignment, that's probably the last > > problem though). Despite its also significant drawbacks and the > > complexity of the change, probably the 4M pagetables would be the saner > > approch to manage more efficiently 64G with only a 800M kernel window. > > Though that'd reduce the size of some of the structures, I'd still > have other concerns (such as tlb size, which is something stupid > like 4 pages, IIRC), and the space wastage you mentioned. Page > clustering is probably a more useful technique - letting the existing > control structures control groups of pages. For example, one struct > page could control aligned groups of 4 4K pages, giving us an > effective page size of 16K from the management overhead point of > view (swap in and out in 4 page chunks, etc).
IMHO, this will be a much easier change than storing mem_map in highmem, and solves 75% of the problem. It's not just ia32 numa that will benefit from it. For example, MIPS supports 16K pages in software, which will take a lot of load off the tlb. According to Ralf, there are benefits re virtual aliasing as well.
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