On 10/5/18 12:49 PM, 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. > > After the call sites are changed, then these routines will be updated to do more. > [2], above has slightly more detail about that. > > Also, I plan to respin again pretty soon, because someone politely pointed out offline that even in this small patchset, I've botched the handling of the --npages loop, sigh. (Thanks, Ralph!) The original form: while(--npages) was correct, but now it's not so much. thanks, -- John Hubbard NVIDIA
