Messages in this thread | | | From | (Linus Torvalds) | Subject | Re: changing mm->mmap_sem (was: Re: system call for process information?) | Date | 18 Mar 2001 10:13:11 -0800 |
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In article <Pine.LNX.4.21.0103181122480.13050-100000@imladris.rielhome.conectiva>, Rik van Riel <riel@conectiva.com.br> wrote: > >OK, I'll write some code to prevent multiple threads from >stepping all over each other when they pagefault at the >same address. > >What would be the preferred method of fixing this ? > >- fixing do_swap_page and all ->nopage functions
There is no need to fix gthe "nopage" functions. They never see the page table directly anyway.
So the only thing that _should_ be needed is to make sure that do_no_page(), do_swap_page() and do_anonymous_page() will re-aquire the mm->page_table_lock and undo their work if it turns out that the page table entry is no longer empty..
(do_wp_page() should already be ok in this regard - it already does this exactly because present pagetable entries can already race with kswapd. What we're adding is that _nonpresent_ page table entries can race with multiple invocations of concurrent page faults)
>- hacking handle_mm_fault to make sure no overlapping > pagefaults will be served at the same time
No. The whole reason the rw_semaphores were done in the first place was to allow page faults to happen concurrently to allow threaded applictions to scale up even when faulting.
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