On 12/3/18 11:53 PM, Mike Rapoport wrote: > Hi John, > > Thanks for having documentation as a part of the patch. Some kernel-doc > nits below. > > On Mon, Dec 03, 2018 at 04:17:19PM -0800, 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(), and also as a replacement >> for open-coded loops that release multiple pages. >> These may be used for subsequent performance improvements, >> via batching of pages to be released. >> >> This is the first step of fixing the problem described in [1]. The steps >> are: >> >> 1) (This patch): provide put_user_page*() routines, intended to be used >> for releasing pages that were pinned via get_user_pages*(). >> >> 2) Convert all of the call sites for get_user_pages*(), to >> invoke put_user_page*(), instead of put_page(). This involves dozens of >> call sites, and will take some time. >> >> 3) After (2) is complete, use get_user_pages*() and put_user_page*() to >> implement tracking of these pages. This tracking will be separate from >> the existing struct page refcounting. >> >> 4) Use the tracking and identification of these pages, to implement >> special handling (especially in writeback paths) when the pages are >> backed by a filesystem. Again, [1] provides details as to why that is >> desirable. >> >> [1] https://lwn.net/Articles/753027/ : "The Trouble with get_user_pages()" >> >> Reviewed-by: Jan Kara <jack@xxxxxxx> >> >> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx> >> Cc: Michal Hocko <mhocko@xxxxxxxxxx> >> Cc: Christopher Lameter <cl@xxxxxxxxx> >> Cc: Jason Gunthorpe <jgg@xxxxxxxx> >> Cc: Dan Williams <dan.j.williams@xxxxxxxxx> >> Cc: Jan Kara <jack@xxxxxxx> >> Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx> >> Cc: Jerome Glisse <jglisse@xxxxxxxxxx> >> Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx> >> Cc: Ralph Campbell <rcampbell@xxxxxxxxxx> >> Signed-off-by: John Hubbard <jhubbard@xxxxxxxxxx> >> --- >> include/linux/mm.h | 20 ++++++++++++ >> mm/swap.c | 80 ++++++++++++++++++++++++++++++++++++++++++++++ >> 2 files changed, 100 insertions(+) >> >> diff --git a/include/linux/mm.h b/include/linux/mm.h >> index 5411de93a363..09fbb2c81aba 100644 >> --- a/include/linux/mm.h >> +++ b/include/linux/mm.h >> @@ -963,6 +963,26 @@ static inline void put_page(struct page *page) >> __put_page(page); >> } >> >> +/* >> + * put_user_page() - release a page that had previously been acquired via >> + * a call to one of the get_user_pages*() functions. > > Please add @page parameter description, otherwise kernel-doc is unhappy Hi Mike, Sorry I missed these kerneldoc points from your earlier review! I'll fix it up now and it will show up in the next posting. > >> + * >> + * Pages that were pinned via get_user_pages*() must be released via >> + * either put_user_page(), or one of the put_user_pages*() routines >> + * below. This is so that eventually, pages that are pinned via >> + * get_user_pages*() can be separately tracked and uniquely handled. In >> + * particular, interactions with RDMA and filesystems need special >> + * handling. >> + */ >> +static inline void put_user_page(struct page *page) >> +{ >> + put_page(page); >> +} >> + >> +void put_user_pages_dirty(struct page **pages, unsigned long npages); >> +void put_user_pages_dirty_lock(struct page **pages, unsigned long npages); >> +void put_user_pages(struct page **pages, unsigned long npages); >> + >> #if defined(CONFIG_SPARSEMEM) && !defined(CONFIG_SPARSEMEM_VMEMMAP) >> #define SECTION_IN_PAGE_FLAGS >> #endif >> diff --git a/mm/swap.c b/mm/swap.c >> index aa483719922e..bb8c32595e5f 100644 >> --- a/mm/swap.c >> +++ b/mm/swap.c >> @@ -133,6 +133,86 @@ void put_pages_list(struct list_head *pages) >> } >> EXPORT_SYMBOL(put_pages_list); >> >> +typedef int (*set_dirty_func)(struct page *page); >> + >> +static void __put_user_pages_dirty(struct page **pages, >> + unsigned long npages, >> + set_dirty_func sdf) >> +{ >> + unsigned long index; >> + >> + for (index = 0; index < npages; index++) { >> + struct page *page = compound_head(pages[index]); >> + >> + if (!PageDirty(page)) >> + sdf(page); >> + >> + put_user_page(page); >> + } >> +} >> + >> +/* >> + * put_user_pages_dirty() - for each page in the @pages array, make >> + * that page (or its head page, if a compound page) dirty, if it was >> + * previously listed as clean. Then, release the page using >> + * put_user_page(). >> + * >> + * Please see the put_user_page() documentation for details. >> + * >> + * set_page_dirty(), which does not lock the page, is used here. >> + * Therefore, it is the caller's responsibility to ensure that this is >> + * safe. If not, then put_user_pages_dirty_lock() should be called instead. >> + * >> + * @pages: array of pages to be marked dirty and released. >> + * @npages: number of pages in the @pages array. > > Please put the parameters description next to the brief function > description, as described in [1] > > [1] https://www.kernel.org/doc/html/latest/doc-guide/kernel-doc.html#function-documentation > OK. > >> + * >> + */ >> +void put_user_pages_dirty(struct page **pages, unsigned long npages) >> +{ >> + __put_user_pages_dirty(pages, npages, set_page_dirty); >> +} >> +EXPORT_SYMBOL(put_user_pages_dirty); >> + >> +/* >> + * put_user_pages_dirty_lock() - for each page in the @pages array, make >> + * that page (or its head page, if a compound page) dirty, if it was >> + * previously listed as clean. Then, release the page using >> + * put_user_page(). >> + * >> + * Please see the put_user_page() documentation for details. >> + * >> + * This is just like put_user_pages_dirty(), except that it invokes >> + * set_page_dirty_lock(), instead of set_page_dirty(). >> + * >> + * @pages: array of pages to be marked dirty and released. >> + * @npages: number of pages in the @pages array. > > Ditto OK. > >> + * >> + */ >> +void put_user_pages_dirty_lock(struct page **pages, unsigned long npages) >> +{ >> + __put_user_pages_dirty(pages, npages, set_page_dirty_lock); >> +} >> +EXPORT_SYMBOL(put_user_pages_dirty_lock); >> + >> +/* >> + * put_user_pages() - for each page in the @pages array, release the page >> + * using put_user_page(). >> + * >> + * Please see the put_user_page() documentation for details. >> + * >> + * @pages: array of pages to be marked dirty and released. >> + * @npages: number of pages in the @pages array. >> + * > > And here as well :) OK. thanks, -- John Hubbard NVIDIA
