Messages in this thread | | | Date | Thu, 9 Apr 2009 20:13:09 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH 1/1] Document get_user_pages_fast() |
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On Fri, 10 Apr 2009 11:17:22 +0900 (JST) KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> wrote:
> > +/** > > + * get_user_pages_fast() - pin user pages in memory > > + * @start: starting user address > > + * @nr_pages: number of pages from start to pin > > + * @write: whether pages will be written to > > + * @pages: array that receives pointers to the pages pinned. > > + * Should be at least nr_pages long. > > + * > > + * Attempt to pin user pages in memory without taking mm->mmap_sem. > > + * If not successful, it will fall back to taking the lock and > > + * calling get_user_pages(). > > + * > > + * Returns number of pages pinned. This may be fewer than the number > > + * requested. If nr_pages is 0 or negative, returns 0. If no pages > > + * were pinned, returns -errno. > > + */ > > int __attribute__((weak)) get_user_pages_fast(unsigned long start, > > int nr_pages, int write, struct page **pages) > > { > > There is one problem. > gup and get_page() don't provide any page pinning. > > get_page() only gurantee not freed. but don't gurantee to prevent page > reclaim
is_page_cache_freeable() measures page_count()...
> and Cow change owner process.
hm. buggy userspace? Why is that a problem from a kernel perspective?
> Yes, current all gup caller have serious bug. especially direct-io, aio, bio > are broken. > > > >
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