Messages in this thread | | | From | Daniel Phillips <> | Subject | Re: [RFC] Page table sharing | Date | Tue, 19 Feb 2002 13:43:50 +0100 |
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On February 19, 2002 01:22 pm, Hugh Dickins wrote: > On Tue, 19 Feb 2002, Daniel Phillips wrote: > > On February 19, 2002 04:22 am, Linus Torvalds wrote: > > > That still leaves the TLB invalidation issue, but we could handle that > > > with an alternate approach: use the same "free_pte_ctx" kind of gathering > > > that the zap_page_range() code uses for similar reasons (ie gather up the > > > pte entries that you're going to free first, and then do a global > > > invalidate later). > > > > I think I'll fall back to unsharing the page table on swapout as Hugh > > suggested, until we sort this out. > > My proposal was to unshare the page table on read fault, to avoid race. > I suppose you could, just for your current testing, use that technique > in swapout, to avoid the much more serious TLB issue that Linus has now > raised. But don't do so without realizing that it is a very deadlocky > idea for swapout (making pages freeable) to need to allocate pages.
I didn't fail to notice that. It's no worse than any other page reservation issue, of which we have plenty. One day we're going to have to solve them all.
> And it's not much use for swapout to skip them either, since the shared > page tables become valuable on the very large address spaces which we'd > want swapout to be hitting.
Unsharing is the route of least resistance at the moment. If necessary I can keep a page around for that purpose, then reestablish that reserve after using it.
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