Messages in this thread | | | Date | Sun, 14 Mar 2004 01:02:39 -0800 | From | Andrew Morton <> | Subject | Re: [Lse-tech] Re: Hugetlbpages in very large memory machines....... |
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Andrew Morton <akpm@osdl.org> wrote: > > Well that's just a dumb implementation. hugetlb_prefault() doesn't need > page_table_lock while it is zeroing the page: just drop it, test for > -EEXIST returned from add_to_page_cache(). > > In fact we need to do that anyway: the current code is buggy if some other > process with a different mm gets in there and instantiates the page in the > pagecache before this process does: hugetlb_prefault() will return -EEXIST > instead of simply accepting the race and using the page which someone else > put there. > > After we have the page in pagecache we need to retake page_table_lock and > check that the target pte is still pte_none(). If it is not, you know that > some other thread has already instantiated a pte there so the new ref to > the pagecache page can simply be dropped. See how do_no_page() handles it. > Of course, this only applies if mmap_sem is no longer held in there.
But before implementing any of this we should move hugetlb_prefault() and any other generic-looking functions into mm/hugetlbpage.c. We're getting too much duplication in there.
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