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. After the call sites are changed, then these routines will be updated to do more. [2], above has slightly more detail about that. thanks, -- John Hubbard NVIDIA
