On 10/5/18 2:48 PM, Jason Gunthorpe wrote: > On Fri, Oct 05, 2018 at 12:49:06PM -0700, John Hubbard wrote: >> On 10/5/18 8:17 AM, Jason Gunthorpe wrote: >>> On Thu, Oct 04, 2018 at 09:02:24PM -0700, john.hubbard@xxxxxxxxx wrote: >>>> From: John Hubbard <jhubbard@xxxxxxxxxx> >>>> >>>> Introduces put_user_page(), which simply calls put_page(). >>>> This provides a way to update all get_user_pages*() callers, >>>> so that they call put_user_page(), instead of put_page(). >>>> >>>> Also introduces put_user_pages(), and a few dirty/locked variations, >>>> as a replacement for release_pages(), for the same reasons. >>>> These may be used for subsequent performance improvements, >>>> via batching of pages to be released. >>>> >>>> This prepares for eventually fixing the problem described >>>> in [1], and is following a plan listed in [2], [3], [4]. >>>> >>>> [1] https://lwn.net/Articles/753027/ : "The Trouble with get_user_pages()" >>>> >>>> [2] https://lkml.kernel.org/r/20180709080554.21931-1-jhubbard@xxxxxxxxxx >>>> Proposed steps for fixing get_user_pages() + DMA problems. >>>> >>>> [3]https://lkml.kernel.org/r/20180710082100.mkdwngdv5kkrcz6n@xxxxxxxxxxxxxx >>>> Bounce buffers (otherwise [2] is not really viable). >>>> >>>> [4] https://lkml.kernel.org/r/20181003162115.GG24030@xxxxxxxxxxxxxx >>>> Follow-up discussions. >>>> >> [...] >>>> >>>> +/* Placeholder version, until all get_user_pages*() callers are updated. */ >>>> +static inline void put_user_page(struct page *page) >>>> +{ >>>> + put_page(page); >>>> +} >>>> + >>>> +/* For get_user_pages*()-pinned pages, use these variants instead of >>>> + * release_pages(): >>>> + */ >>>> +static inline void put_user_pages_dirty(struct page **pages, >>>> + unsigned long npages) >>>> +{ >>>> + while (npages) { >>>> + set_page_dirty(pages[npages]); >>>> + put_user_page(pages[npages]); >>>> + --npages; >>>> + } >>>> +} >>> >>> Shouldn't these do the !PageDirty(page) thing? >>> >> >> Well, not yet. This is the "placeholder" patch, in which I planned to keep >> the behavior the same, while I go to all the get_user_pages call sites and change >> put_page() and release_pages() over to use these new routines. > > Hmm.. Well, if it is the right thing to do here, why not include it and > take it out of callers when doing the conversion? > > If it is the wrong thing, then let us still take it out of callers > when doing the conversion :) > > Just seems like things will be in a better place to make future > changes if all the call sights are de-duplicated and correct. > OK, yes. Let me send out a v3 with that included, then. thanks, -- John Hubbard NVIDIA
