Messages in this thread |  | | | Date | Fri, 6 Dec 2002 16:30:25 -0800 | | From | William Lee Irwin III <> | | Subject | Re: Maybe a VM bug in 2.4.18-18 from RH 8.0? |
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At some point in the past, I wrote: > My point is that making any distinction will lead to inevitable > fragmentation of memory.
It's mostly userspace; the kernel is usually (hello drivers/ !) cautious and uses slab.c's anti-internal fragmentation techniques for most structs.
At some point in the past, I wrote: >> Hmm, from the appearances of the patch (my ability to test the patch >> is severely hampered by its age) it should actually maintain hardware >> pagesize mmap() granularity, ABI compatibility, etc.
On Sat, Dec 07, 2002 at 12:50:32AM +0100, Andrea Arcangeli wrote: > If it only implements the MMUPAGE_SIZE, yes, it can. > You break the ABI as soon as you change the kernel wide PAGE_SIZE. it is > allowed only on 64bit binaries running on a x86-64 kernel. The 32bit > binaries running in compatibility mode as said would suffer a bit, but > most things should run and we can make hacks like using anon mappings if > the files are small just for the sake of running some app 32bit (like we > use anon mappings for a.out binaries needing 1k offsets today).
I'm not sure what to make of this. The distinction and PTE vectoring API (AFAICT) allows PTE's to map sub-PAGE_SIZE-sized (MMUPAGE_SIZE to be exact) regions. Someone start screaming if I misread the patch.
On Sat, Dec 07, 2002 at 12:50:32AM +0100, Andrea Arcangeli wrote: > Said that even the MMUPAGE_SIZE alone would be useful, but I'd prefer if > the kernel wide PAGE_SIZE would be increased (with the disavantage of > breaking the ABI, but it would be a config option, even the 2G/3.5G/1G > split has the chance of breaking some app despite I wouldn't classify it > as an ABI violation for the reason explained in one of the last emails).
Userspace is required to have >= 3GB of virtualspace, according to the SVR4 i386 ABI spec. But we don't follow that strictly anyway.
At some point in the past, I wrote: >> I think this is a perfect example of how the increased awareness of >> space consumption highmem gives us helps us optimize all boxen.
On Sat, Dec 07, 2002 at 12:50:32AM +0100, Andrea Arcangeli wrote: > In this case funnily it has a chance to help some 64bit boxes too ;).
I've heard the sizeof(mem_map) footprint is worse on 64-bit because while PAGE_SIZE remains the same, but pointers double in size. This would help a bit there, too.
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