Messages in this thread | | | Date | Wed, 24 Sep 2008 20:11:08 +0100 | From | Mel Gorman <> | Subject | Re: [PATCH 1/2] Report the pagesize backing a VMA in /proc/pid/smaps |
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On (24/09/08 11:59), Dave Hansen didst pronounce: > On Wed, 2008-09-24 at 18:10 +0100, Mel Gorman wrote: > > On (24/09/08 09:06), Dave Hansen didst pronounce: > > > On Wed, 2008-09-24 at 16:41 +0100, Mel Gorman wrote: > > > > I admit it's ppc64-specific. In the latest patch series, I made this a > > > > separate patch so that it could be readily dropped again for this reason. > > > > Maybe an alternative would be to display MMUPageSize *only* where it differs > > > > from KernelPageSize. Would that be better or similarly confusing? > > > > > > I would also think that any arch implementing fallback from large to > > > small pages in a hugetlbfs area (Adam needs to post his patches :) would > > > also use this. > > > > > > > Fair point. Maybe the thing to do is backburner this patch for the moment and > > reintroduce it when/if an architecture supports demotion? The KernelPageSize > > reporting in smaps and what the hpagesize in maps is still useful though > > I believe. Any comment? > > I'd kinda prefer to see it normalized into a single place rather than > sprinkle it in each smaps file.
I don't get what you mean by it being sprinkled in each smaps file. How would you present the data?
> We should be able to figure out which > mount the file is from and, from there, maybe we need some per-mount > information exported. >
Per-mount information is already exported and you can infer the data about huge pagesizes. For example, if you know the default huge pagesize (from /proc/meminfo), and the file is on hugetlbfs (read maps, then /proc/mounts) and there is no pagesize= mount option (mounts again), you could guess what the hugepage that is backing a VMA is. Shared memory segments are a little harder but again, you can infer the information if you look around for long enough.
However, this is awkward and not very user-friendly. With the patches (minus MMUPageSize as I think we've agreed to postpone that), it's easy to see what pagesize is being used at a glance. Without it, you need to know a fair bit about hugepages are implemented in Linux to infer the information correctly.
> > (future stuff from here on) > > > > In the future if demotion does happen then the MMUPageSize information may > > be genuinely useful instead of just a curious oddity on ppc64. As you point > > out, Adam (added to cc) has worked on this area (starting with x86 demotion) > > in the past but it's a while before it'll be considered for merging I believe. > > > > That aside, more would need to be done with the page size reporting then > > anyway. For example, it maybe indicate how much of each pagesize is in a VMA > > or indicate that KernelPageSize is what is being requested but in reality > > it is mixed like; > > > > KernelPageSize: 2048 kB (mixed) > > > > or > > > > KernelPageSize: 2048 kB * 5, 4096 kB * 20 > > Looks a bit verbose, but I agree with the sentiment. >
Grand, I'll keep note of this to revisit it in the future when/if pagesizes get mixed in a VMA. Thanks
-- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab
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