Messages in this thread Patch in this message | | | Subject | Re: [RFC] page fault retry with NOPAGE_RETRY | From | Benjamin Herrenschmidt <> | Date | Sun, 24 Sep 2006 08:35:36 +1000 |
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> Perhaps we should concentrate on that for now. Did we have a patch to look > at?
Only a hand written proto-patch. Below is a real (but untested) one. Note that there might be still issues when called from get_user_pages() which of course won't go back to userland. For the two usage scenario I have in mind, it should be ok though. One (a signal pending) will loop back in until the resource is available, the other (no_page() inserts the PTE itself) is just fine. For the former case, I've added a cond_resched() to the loop, we might want to look into adding the info of wether we are coming from get_user_pages() vs. do_page_fault() to these new arguments you want to add to page fault handlers. That would allow in our case to do a non-interruptibe sleep when caused by get_user_pages().
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Add a way for a no_page() handler to request a retry of the faulting instruction. It goes back to userland on page faults and just tries again in get_user_pages(). I added a cond_resched() in the loop in that later case.
Signed-off-by: Benjamin Herrenchmidt <benh@kernel.crashing.org>
Index: linux-work/include/linux/mm.h =================================================================== --- linux-work.orig/include/linux/mm.h 2006-08-30 08:51:21.000000000 +1000 +++ linux-work/include/linux/mm.h 2006-09-24 08:25:33.000000000 +1000 @@ -623,6 +623,7 @@ */ #define NOPAGE_SIGBUS (NULL) #define NOPAGE_OOM ((struct page *) (-1)) +#define NOPAGE_RETRY ((struct page *) (-2)) /* * Different kinds of faults, as returned by handle_mm_fault(). Index: linux-work/mm/memory.c =================================================================== --- linux-work.orig/mm/memory.c 2006-08-17 16:16:06.000000000 +1000 +++ linux-work/mm/memory.c 2006-09-24 08:34:09.000000000 +1000 @@ -1081,6 +1081,7 @@ default: BUG(); } + cond_resched(); } if (pages) { pages[i] = page; @@ -2117,11 +2118,13 @@ * after the next truncate_count read. */ - /* no page was available -- either SIGBUS or OOM */ - if (new_page == NOPAGE_SIGBUS) + /* no page was available -- either SIGBUS, OOM or RETRY */ + if (unlikely(new_page == NOPAGE_SIGBUS)) return VM_FAULT_SIGBUS; - if (new_page == NOPAGE_OOM) + else if (unlikely(new_page == NOPAGE_OOM)) return VM_FAULT_OOM; + else if (unlikely(new_page == NOPAGE_RETRY)) + return VM_FAULT_MINOR; /* * Should we do an early C-O-W break?
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