Messages in this thread | | | Subject | Re: [patch] mm: reduce pagetable-freeing latencies | From | Benjamin Herrenschmidt <> | Date | Wed, 25 Jul 2007 20:08:13 +1000 |
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On Wed, 2007-07-25 at 11:46 +0200, Andi Kleen wrote: > > You could perhaps use C99 variable length arrays to avoid the stack > > waste when not needed, however Andi once told me that generates rather > > dubious code. > > It generates frame pointers, but that's not that bad. I'm not > aware of any other bad side effects. Ok the compiler will limit > your goto usage, but that's more a good thing. > > But since you always have to strictly limit the array in kernel code anyways > you could as well just allocate the fixed limit.
Plan is fixed array or 4 or maybe 8 entries (pointers), that shouldn't be -too- bad. The code path I'm a bit worried about is unmap_mapping_ranges() which goes into zapping page tables from deep within filesystems.
At worst, I can reduce the fixed array to 1 entry. That means that if the batch can't manage to get a page to use for the page list, it will end up doing the flush for each page :-) But that should rarely happen, in fact, I would expect it to be able to get a page the next time around because it just freed one...
Ben.
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