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SubjectRe: [PATCH v2 2/3] mm: introduce put_user_page[s](), placeholder versions
On Thu, Oct 04, 2018 at 09:02:24PM -0700, john.hubbard@gmail.com wrote:
> From: John Hubbard <jhubbard@nvidia.com>
>
> 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@nvidia.com
> Proposed steps for fixing get_user_pages() + DMA problems.
>
> [3]https://lkml.kernel.org/r/20180710082100.mkdwngdv5kkrcz6n@quack2.suse.cz
> Bounce buffers (otherwise [2] is not really viable).
>
> [4] https://lkml.kernel.org/r/20181003162115.GG24030@quack2.suse.cz
> Follow-up discussions.
>
> CC: Matthew Wilcox <willy@infradead.org>
> CC: Michal Hocko <mhocko@kernel.org>
> CC: Christopher Lameter <cl@linux.com>
> CC: Jason Gunthorpe <jgg@ziepe.ca>
> CC: Dan Williams <dan.j.williams@intel.com>
> CC: Jan Kara <jack@suse.cz>
> CC: Al Viro <viro@zeniv.linux.org.uk>
> CC: Jerome Glisse <jglisse@redhat.com>
> CC: Christoph Hellwig <hch@infradead.org>
> Signed-off-by: John Hubbard <jhubbard@nvidia.com>
> include/linux/mm.h | 42 ++++++++++++++++++++++++++++++++++++++++--
> 1 file changed, 40 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index a61ebe8ad4ca..1a9aae7c659f 100644
> +++ b/include/linux/mm.h
> @@ -137,6 +137,8 @@ extern int overcommit_ratio_handler(struct ctl_table *, int, void __user *,
> size_t *, loff_t *);
> extern int overcommit_kbytes_handler(struct ctl_table *, int, void __user *,
> size_t *, loff_t *);
> +int set_page_dirty(struct page *page);
> +int set_page_dirty_lock(struct page *page);
>
> #define nth_page(page,n) pfn_to_page(page_to_pfn((page)) + (n))
>
> @@ -943,6 +945,44 @@ static inline void put_page(struct page *page)
> __put_page(page);
> }
>
> +/* 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?

Jason

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