Messages in this thread | | | Subject | Re: [RFC] Page table sharing | From | (Eric W. Biederman) | Date | 18 Feb 2002 21:27:11 -0700 |
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Daniel Phillips <phillips@bonn-fries.net> writes:
> On February 19, 2002 01:03 am, Hugh Dickins wrote: > > On Tue, 19 Feb 2002, Daniel Phillips wrote: > > > On February 18, 2002 08:04 pm, Hugh Dickins wrote: > > > > On Mon, 18 Feb 2002, Daniel Phillips wrote: > > > > > On February 18, 2002 09:09 am, Hugh Dickins wrote: > > > > > > Since copy_page_range would not copy shared page tables, I'm wrong to > > > > > > point there. But __pte_alloc does copy shared page tables (to unshare > > > > > > > them), and needs them to be stable while it does so: so locking > against > > > > > > > swap_out really is required. It also needs locking against read > faults, > > > > > > > and they against each other: but there I imagine it's just a matter of > > > > > > > dropping the write arg to __pte_alloc, going back to pte_alloc again. > > > > > > I'm not sure what you mean here, you're not suggesting we should unshare the > > > > page table on read fault are you? > > > > I am. But I can understand that you'd prefer not to do it that way. > > Hugh > > No, that's not nearly studly enough ;-) > > Since we have gone to all the trouble of sharing the page table, we should > swap in/out for all sharers at the same time. That is, keep it shared, saving > memory and cpu. > > Now I finally see what you were driving at: before, we could count on the > mm->page_table_lock for exclusion on read fault, now we can't, at least not > when ptb->count is great than one[1]. So let's come up with something nice as > a substitute, any suggestions? > > [1] I think that's a big, broad hint.
Something like: struct mm_share { spinlock_t page_table_lock; struct list_head mm_list; };
struct mm { struct list_head mm_list; struct mm_share *mm_share; ..... };
So we have an overarching structure for all of the shared mm's.
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