Just as a side note, can you please CC me on the whole series next time? Because this time I had to look up e.g. the introductory email in the mailing list... Thanks!
On Sat 10-11-18 00:50:41, john.hubb...@gmail.com wrote: > From: John Hubbard <jhubb...@nvidia.com> > > This patch sets and restores the new page->dma_pinned_flags and > page->dma_pinned_count fields, but does not actually use them for > anything yet. > > In order to use these fields at all, the page must be removed from > any LRU list that it's on. The patch also adds some precautions that > prevent the page from getting moved back onto an LRU, once it is > in this state. > > This is in preparation to fix some problems that came up when using > devices (NICs, GPUs, for example) that set up direct access to a chunk > of system (CPU) memory, so that they can DMA to/from that memory. > > Cc: Matthew Wilcox <wi...@infradead.org> > Cc: Michal Hocko <mho...@kernel.org> > Cc: Christopher Lameter <c...@linux.com> > Cc: Jason Gunthorpe <j...@ziepe.ca> > Cc: Dan Williams <dan.j.willi...@intel.com> > Cc: Jan Kara <j...@suse.cz> > Signed-off-by: John Hubbard <jhubb...@nvidia.com> > --- > include/linux/mm.h | 19 +++++---------- > mm/gup.c | 55 +++++++++++++++++++++++++++++++++++++++++-- > mm/memcontrol.c | 8 +++++++ > mm/swap.c | 58 ++++++++++++++++++++++++++++++++++++++++++++++ > 4 files changed, 125 insertions(+), 15 deletions(-) > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index 09fbb2c81aba..6c64b1e0b777 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -950,6 +950,10 @@ static inline void put_page(struct page *page) > { > page = compound_head(page); > > + VM_BUG_ON_PAGE(PageDmaPinned(page) && > + page_ref_count(page) < > + atomic_read(&page->dma_pinned_count), > + page); > /* > * For devmap managed pages we need to catch refcount transition from > * 2 to 1, when refcount reach one it means the page is free and we > @@ -964,21 +968,10 @@ static inline void put_page(struct page *page) > } > > /* > - * put_user_page() - release a page that had previously been acquired via > - * a call to one of the get_user_pages*() functions. > - * > * 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. > + * one of these put_user_pages*() routines: > */ > -static inline void put_user_page(struct page *page) > -{ > - put_page(page); > -} > - > +void put_user_page(struct 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); > diff --git a/mm/gup.c b/mm/gup.c > index 55a41dee0340..ec1b26591532 100644 > --- a/mm/gup.c > +++ b/mm/gup.c > @@ -25,6 +25,50 @@ struct follow_page_context { > unsigned int page_mask; > }; > > +static void pin_page_for_dma(struct page *page) > +{ > + int ret = 0; > + struct zone *zone; > + > + page = compound_head(page); > + zone = page_zone(page); > + > + spin_lock(zone_gup_lock(zone)); A think you'll need irqsafe lock here as get_user_pages_fast() can get called from interrupt context in some cases. And so can put_user_page()... <snip> > +/* > + * put_user_page() - release a page that had previously been acquired via > + * a call to one of the get_user_pages*() functions. > + * > + * Usage: 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. > + */ > +void put_user_page(struct page *page) > +{ > + struct zone *zone = page_zone(page); > + > + page = compound_head(page); > + > + if (atomic_dec_and_test(&page->dma_pinned_count)) { > + spin_lock(zone_gup_lock(zone)); > + /* Re-check while holding the lock, because > + * pin_page_for_dma() or get_page() may have snuck in right > + * after the atomic_dec_and_test, and raised the count > + * above zero again. If so, just leave the flag set. And > + * because the atomic_dec_and_test above already got the > + * accounting correct, no other action is required. > + */ > + VM_BUG_ON_PAGE(PageLRU(page), page); > + VM_BUG_ON_PAGE(!PageDmaPinned(page), page); > + > + if (atomic_read(&page->dma_pinned_count) == 0) { We have atomic_dec_and_lock[_irqsave]() exactly for constructs like this. > + ClearPageDmaPinned(page); > + > + if (PageDmaPinnedWasLru(page)) { > + ClearPageDmaPinnedWasLru(page); > + putback_lru_page(page); > + } > + } > + > + spin_unlock(zone_gup_lock(zone)); > + } > + > + put_page(page); > +} > +EXPORT_SYMBOL(put_user_page); > + Honza -- Jan Kara <j...@suse.com> SUSE Labs, CR