| Message ID | 20190804224915.28669-2-jhubbard@nvidia.com |
|---|---|
| State | Not Applicable |
| Delegated to: | David Miller |
| Headers | show |
| Series | put_user_pages(): miscellaneous call sites | expand |
On Sun, Aug 04, 2019 at 03:48:42PM -0700, john.hubbard@gmail.com wrote: > From: John Hubbard <jhubbard@nvidia.com> > > Provide a more capable variation of put_user_pages_dirty_lock(), > and delete put_user_pages_dirty(). This is based on the > following: > > 1. Lots of call sites become simpler if a bool is passed > into put_user_page*(), instead of making the call site > choose which put_user_page*() variant to call. > > 2. Christoph Hellwig's observation that set_page_dirty_lock() > is usually correct, and set_page_dirty() is usually a > bug, or at least questionable, within a put_user_page*() > calling chain. > > This leads to the following API choices: > > * put_user_pages_dirty_lock(page, npages, make_dirty) > > * There is no put_user_pages_dirty(). You have to > hand code that, in the rare case that it's > required. > > Reviewed-by: Christoph Hellwig <hch@lst.de> > Cc: Matthew Wilcox <willy@infradead.org> > Cc: Jan Kara <jack@suse.cz> > Cc: Ira Weiny <ira.weiny@intel.com> > Cc: Jason Gunthorpe <jgg@ziepe.ca> > Signed-off-by: John Hubbard <jhubbard@nvidia.com> > --- > drivers/infiniband/core/umem.c | 5 +- > drivers/infiniband/hw/hfi1/user_pages.c | 5 +- > drivers/infiniband/hw/qib/qib_user_pages.c | 13 +-- > drivers/infiniband/hw/usnic/usnic_uiom.c | 5 +- > drivers/infiniband/sw/siw/siw_mem.c | 19 +--- > include/linux/mm.h | 5 +- > mm/gup.c | 115 +++++++++------------ > 7 files changed, 61 insertions(+), 106 deletions(-) > > diff --git a/drivers/infiniband/core/umem.c b/drivers/infiniband/core/umem.c > index 08da840ed7ee..965cf9dea71a 100644 > --- a/drivers/infiniband/core/umem.c > +++ b/drivers/infiniband/core/umem.c > @@ -54,10 +54,7 @@ static void __ib_umem_release(struct ib_device *dev, struct ib_umem *umem, int d > > for_each_sg_page(umem->sg_head.sgl, &sg_iter, umem->sg_nents, 0) { > page = sg_page_iter_page(&sg_iter); > - if (umem->writable && dirty) > - put_user_pages_dirty_lock(&page, 1); > - else > - put_user_page(page); > + put_user_pages_dirty_lock(&page, 1, umem->writable && dirty); > } > > sg_free_table(&umem->sg_head); > diff --git a/drivers/infiniband/hw/hfi1/user_pages.c b/drivers/infiniband/hw/hfi1/user_pages.c > index b89a9b9aef7a..469acb961fbd 100644 > --- a/drivers/infiniband/hw/hfi1/user_pages.c > +++ b/drivers/infiniband/hw/hfi1/user_pages.c > @@ -118,10 +118,7 @@ int hfi1_acquire_user_pages(struct mm_struct *mm, unsigned long vaddr, size_t np > void hfi1_release_user_pages(struct mm_struct *mm, struct page **p, > size_t npages, bool dirty) > { > - if (dirty) > - put_user_pages_dirty_lock(p, npages); > - else > - put_user_pages(p, npages); > + put_user_pages_dirty_lock(p, npages, dirty); > > if (mm) { /* during close after signal, mm can be NULL */ > atomic64_sub(npages, &mm->pinned_vm); > diff --git a/drivers/infiniband/hw/qib/qib_user_pages.c b/drivers/infiniband/hw/qib/qib_user_pages.c > index bfbfbb7e0ff4..26c1fb8d45cc 100644 > --- a/drivers/infiniband/hw/qib/qib_user_pages.c > +++ b/drivers/infiniband/hw/qib/qib_user_pages.c > @@ -37,15 +37,6 @@ > > #include "qib.h" > > -static void __qib_release_user_pages(struct page **p, size_t num_pages, > - int dirty) > -{ > - if (dirty) > - put_user_pages_dirty_lock(p, num_pages); > - else > - put_user_pages(p, num_pages); > -} > - > /** > * qib_map_page - a safety wrapper around pci_map_page() > * > @@ -124,7 +115,7 @@ int qib_get_user_pages(unsigned long start_page, size_t num_pages, > > return 0; > bail_release: > - __qib_release_user_pages(p, got, 0); > + put_user_pages_dirty_lock(p, got, false); > bail: > atomic64_sub(num_pages, ¤t->mm->pinned_vm); > return ret; > @@ -132,7 +123,7 @@ int qib_get_user_pages(unsigned long start_page, size_t num_pages, > > void qib_release_user_pages(struct page **p, size_t num_pages) > { > - __qib_release_user_pages(p, num_pages, 1); > + put_user_pages_dirty_lock(p, num_pages, true); > > /* during close after signal, mm can be NULL */ > if (current->mm) > diff --git a/drivers/infiniband/hw/usnic/usnic_uiom.c b/drivers/infiniband/hw/usnic/usnic_uiom.c > index 0b0237d41613..62e6ffa9ad78 100644 > --- a/drivers/infiniband/hw/usnic/usnic_uiom.c > +++ b/drivers/infiniband/hw/usnic/usnic_uiom.c > @@ -75,10 +75,7 @@ static void usnic_uiom_put_pages(struct list_head *chunk_list, int dirty) > for_each_sg(chunk->page_list, sg, chunk->nents, i) { > page = sg_page(sg); > pa = sg_phys(sg); > - if (dirty) > - put_user_pages_dirty_lock(&page, 1); > - else > - put_user_page(page); > + put_user_pages_dirty_lock(&page, 1, dirty); > usnic_dbg("pa: %pa\n", &pa); > } > kfree(chunk); > diff --git a/drivers/infiniband/sw/siw/siw_mem.c b/drivers/infiniband/sw/siw/siw_mem.c > index 67171c82b0c4..1e197753bf2f 100644 > --- a/drivers/infiniband/sw/siw/siw_mem.c > +++ b/drivers/infiniband/sw/siw/siw_mem.c > @@ -60,20 +60,6 @@ struct siw_mem *siw_mem_id2obj(struct siw_device *sdev, int stag_index) > return NULL; > } > > -static void siw_free_plist(struct siw_page_chunk *chunk, int num_pages, > - bool dirty) > -{ > - struct page **p = chunk->plist; > - > - while (num_pages--) { > - if (!PageDirty(*p) && dirty) > - put_user_pages_dirty_lock(p, 1); > - else > - put_user_page(*p); > - p++; > - } > -} > - > void siw_umem_release(struct siw_umem *umem, bool dirty) > { > struct mm_struct *mm_s = umem->owning_mm; > @@ -82,8 +68,9 @@ void siw_umem_release(struct siw_umem *umem, bool dirty) > for (i = 0; num_pages; i++) { > int to_free = min_t(int, PAGES_PER_CHUNK, num_pages); > > - siw_free_plist(&umem->page_chunk[i], to_free, > - umem->writable && dirty); > + put_user_pages_dirty_lock(umem->page_chunk[i].plist, > + to_free, > + umem->writable && dirty); > kfree(umem->page_chunk[i].plist); > num_pages -= to_free; > } > diff --git a/include/linux/mm.h b/include/linux/mm.h > index 0334ca97c584..9759b6a24420 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -1057,8 +1057,9 @@ 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_dirty_lock(struct page **pages, unsigned long npages, > + bool make_dirty); > + > void put_user_pages(struct page **pages, unsigned long npages); > > #if defined(CONFIG_SPARSEMEM) && !defined(CONFIG_SPARSEMEM_VMEMMAP) > diff --git a/mm/gup.c b/mm/gup.c > index 98f13ab37bac..7fefd7ab02c4 100644 > --- a/mm/gup.c > +++ b/mm/gup.c > @@ -29,85 +29,70 @@ struct follow_page_context { > unsigned int page_mask; > }; > > -typedef int (*set_dirty_func_t)(struct page *page); > - > -static void __put_user_pages_dirty(struct page **pages, > - unsigned long npages, > - set_dirty_func_t sdf) > -{ > - unsigned long index; > - > - for (index = 0; index < npages; index++) { > - struct page *page = compound_head(pages[index]); > - > - /* > - * Checking PageDirty at this point may race with > - * clear_page_dirty_for_io(), but that's OK. Two key cases: > - * > - * 1) This code sees the page as already dirty, so it skips > - * the call to sdf(). That could happen because > - * clear_page_dirty_for_io() called page_mkclean(), > - * followed by set_page_dirty(). However, now the page is > - * going to get written back, which meets the original > - * intention of setting it dirty, so all is well: > - * clear_page_dirty_for_io() goes on to call > - * TestClearPageDirty(), and write the page back. > - * > - * 2) This code sees the page as clean, so it calls sdf(). > - * The page stays dirty, despite being written back, so it > - * gets written back again in the next writeback cycle. > - * This is harmless. > - */ > - if (!PageDirty(page)) > - sdf(page); > - > - put_user_page(page); > - } > -} > - > /** > - * put_user_pages_dirty() - release and dirty an array of gup-pinned pages > - * @pages: array of pages to be marked dirty and released. > + * put_user_pages_dirty_lock() - release and optionally dirty gup-pinned pages > + * @pages: array of pages to be maybe marked dirty, and definitely released. Better would be. @pages: array of pages to be put > * @npages: number of pages in the @pages array. > + * @make_dirty: whether to mark the pages dirty > * > * "gup-pinned page" refers to a page that has had one of the get_user_pages() > * variants called on that page. > * > * 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(). > + * compound page) dirty, if @make_dirty is true, and if the page was previously > + * listed as clean. In any case, releases all pages using put_user_page(), > + * possibly via put_user_pages(), for the non-dirty case. I don't think users of this interface need this level of detail. I think something like. * For each page in the @pages array, release the page. If @make_dirty is * true, mark the page dirty prior to release. > * > * 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. > + * set_page_dirty_lock() is used internally. If instead, set_page_dirty() is > + * required, then the caller should a) verify that this is really correct, > + * because _lock() is usually required, and b) hand code it: > + * set_page_dirty_lock(), put_user_page(). > * > */ > -void put_user_pages_dirty(struct page **pages, unsigned long npages) > +void put_user_pages_dirty_lock(struct page **pages, unsigned long npages, > + bool make_dirty) > { > - __put_user_pages_dirty(pages, npages, set_page_dirty); > -} > -EXPORT_SYMBOL(put_user_pages_dirty); > + unsigned long index; > > -/** > - * put_user_pages_dirty_lock() - release and dirty an array of gup-pinned pages > - * @pages: array of pages to be marked dirty and released. > - * @npages: number of pages in the @pages array. > - * > - * 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(). > - * > - */ > -void put_user_pages_dirty_lock(struct page **pages, unsigned long npages) > -{ > - __put_user_pages_dirty(pages, npages, set_page_dirty_lock); > + /* > + * TODO: this can be optimized for huge pages: if a series of pages is > + * physically contiguous and part of the same compound page, then a > + * single operation to the head page should suffice. > + */ I think this comment belongs to the for loop below... or just something about how to make this and put_user_pages() more efficient. It is odd, that this is the same comment as in put_user_pages()... The code is good. So... Other than the comments. Reviewed-by: Ira Weiny <ira.weiny@intel.com> Ira > + > + if (!make_dirty) { > + put_user_pages(pages, npages); > + return; > + } > + > + for (index = 0; index < npages; index++) { > + struct page *page = compound_head(pages[index]); > + /* > + * Checking PageDirty at this point may race with > + * clear_page_dirty_for_io(), but that's OK. Two key > + * cases: > + * > + * 1) This code sees the page as already dirty, so it > + * skips the call to set_page_dirty(). That could happen > + * because clear_page_dirty_for_io() called > + * page_mkclean(), followed by set_page_dirty(). > + * However, now the page is going to get written back, > + * which meets the original intention of setting it > + * dirty, so all is well: clear_page_dirty_for_io() goes > + * on to call TestClearPageDirty(), and write the page > + * back. > + * > + * 2) This code sees the page as clean, so it calls > + * set_page_dirty(). The page stays dirty, despite being > + * written back, so it gets written back again in the > + * next writeback cycle. This is harmless. > + */ > + if (!PageDirty(page)) > + set_page_dirty_lock(page); > + put_user_page(page); > + } > } > EXPORT_SYMBOL(put_user_pages_dirty_lock); > > -- > 2.22.0 >
On 8/6/19 10:39 AM, Ira Weiny wrote: > On Sun, Aug 04, 2019 at 03:48:42PM -0700, john.hubbard@gmail.com wrote: >> From: John Hubbard <jhubbard@nvidia.com> ... >> - >> /** >> - * put_user_pages_dirty() - release and dirty an array of gup-pinned pages >> - * @pages: array of pages to be marked dirty and released. >> + * put_user_pages_dirty_lock() - release and optionally dirty gup-pinned pages >> + * @pages: array of pages to be maybe marked dirty, and definitely released. > > Better would be. > > @pages: array of pages to be put OK, I'll change to that wording. > >> * @npages: number of pages in the @pages array. >> + * @make_dirty: whether to mark the pages dirty >> * >> * "gup-pinned page" refers to a page that has had one of the get_user_pages() >> * variants called on that page. >> * >> * 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(). >> + * compound page) dirty, if @make_dirty is true, and if the page was previously >> + * listed as clean. In any case, releases all pages using put_user_page(), >> + * possibly via put_user_pages(), for the non-dirty case. > > I don't think users of this interface need this level of detail. I think > something like. > > * For each page in the @pages array, release the page. If @make_dirty is > * true, mark the page dirty prior to release. Yes, it is too wordy, I'll change to that. > ... >> -void put_user_pages_dirty_lock(struct page **pages, unsigned long npages) >> -{ >> - __put_user_pages_dirty(pages, npages, set_page_dirty_lock); >> + /* >> + * TODO: this can be optimized for huge pages: if a series of pages is >> + * physically contiguous and part of the same compound page, then a >> + * single operation to the head page should suffice. >> + */ > > I think this comment belongs to the for loop below... or just something about > how to make this and put_user_pages() more efficient. It is odd, that this is > the same comment as in put_user_pages()... Actually I think I'll just delete the comment entirely, it's just noise really. > > The code is good. So... Other than the comments. > > Reviewed-by: Ira Weiny <ira.weiny@intel.com> Thanks for the review! thanks,
diff --git a/drivers/infiniband/core/umem.c b/drivers/infiniband/core/umem.c index 08da840ed7ee..965cf9dea71a 100644 --- a/drivers/infiniband/core/umem.c +++ b/drivers/infiniband/core/umem.c @@ -54,10 +54,7 @@ static void __ib_umem_release(struct ib_device *dev, struct ib_umem *umem, int d for_each_sg_page(umem->sg_head.sgl, &sg_iter, umem->sg_nents, 0) { page = sg_page_iter_page(&sg_iter); - if (umem->writable && dirty) - put_user_pages_dirty_lock(&page, 1); - else - put_user_page(page); + put_user_pages_dirty_lock(&page, 1, umem->writable && dirty); } sg_free_table(&umem->sg_head); diff --git a/drivers/infiniband/hw/hfi1/user_pages.c b/drivers/infiniband/hw/hfi1/user_pages.c index b89a9b9aef7a..469acb961fbd 100644 --- a/drivers/infiniband/hw/hfi1/user_pages.c +++ b/drivers/infiniband/hw/hfi1/user_pages.c @@ -118,10 +118,7 @@ int hfi1_acquire_user_pages(struct mm_struct *mm, unsigned long vaddr, size_t np void hfi1_release_user_pages(struct mm_struct *mm, struct page **p, size_t npages, bool dirty) { - if (dirty) - put_user_pages_dirty_lock(p, npages); - else - put_user_pages(p, npages); + put_user_pages_dirty_lock(p, npages, dirty); if (mm) { /* during close after signal, mm can be NULL */ atomic64_sub(npages, &mm->pinned_vm); diff --git a/drivers/infiniband/hw/qib/qib_user_pages.c b/drivers/infiniband/hw/qib/qib_user_pages.c index bfbfbb7e0ff4..26c1fb8d45cc 100644 --- a/drivers/infiniband/hw/qib/qib_user_pages.c +++ b/drivers/infiniband/hw/qib/qib_user_pages.c @@ -37,15 +37,6 @@ #include "qib.h" -static void __qib_release_user_pages(struct page **p, size_t num_pages, - int dirty) -{ - if (dirty) - put_user_pages_dirty_lock(p, num_pages); - else - put_user_pages(p, num_pages); -} - /** * qib_map_page - a safety wrapper around pci_map_page() * @@ -124,7 +115,7 @@ int qib_get_user_pages(unsigned long start_page, size_t num_pages, return 0; bail_release: - __qib_release_user_pages(p, got, 0); + put_user_pages_dirty_lock(p, got, false); bail: atomic64_sub(num_pages, ¤t->mm->pinned_vm); return ret; @@ -132,7 +123,7 @@ int qib_get_user_pages(unsigned long start_page, size_t num_pages, void qib_release_user_pages(struct page **p, size_t num_pages) { - __qib_release_user_pages(p, num_pages, 1); + put_user_pages_dirty_lock(p, num_pages, true); /* during close after signal, mm can be NULL */ if (current->mm) diff --git a/drivers/infiniband/hw/usnic/usnic_uiom.c b/drivers/infiniband/hw/usnic/usnic_uiom.c index 0b0237d41613..62e6ffa9ad78 100644 --- a/drivers/infiniband/hw/usnic/usnic_uiom.c +++ b/drivers/infiniband/hw/usnic/usnic_uiom.c @@ -75,10 +75,7 @@ static void usnic_uiom_put_pages(struct list_head *chunk_list, int dirty) for_each_sg(chunk->page_list, sg, chunk->nents, i) { page = sg_page(sg); pa = sg_phys(sg); - if (dirty) - put_user_pages_dirty_lock(&page, 1); - else - put_user_page(page); + put_user_pages_dirty_lock(&page, 1, dirty); usnic_dbg("pa: %pa\n", &pa); } kfree(chunk); diff --git a/drivers/infiniband/sw/siw/siw_mem.c b/drivers/infiniband/sw/siw/siw_mem.c index 67171c82b0c4..1e197753bf2f 100644 --- a/drivers/infiniband/sw/siw/siw_mem.c +++ b/drivers/infiniband/sw/siw/siw_mem.c @@ -60,20 +60,6 @@ struct siw_mem *siw_mem_id2obj(struct siw_device *sdev, int stag_index) return NULL; } -static void siw_free_plist(struct siw_page_chunk *chunk, int num_pages, - bool dirty) -{ - struct page **p = chunk->plist; - - while (num_pages--) { - if (!PageDirty(*p) && dirty) - put_user_pages_dirty_lock(p, 1); - else - put_user_page(*p); - p++; - } -} - void siw_umem_release(struct siw_umem *umem, bool dirty) { struct mm_struct *mm_s = umem->owning_mm; @@ -82,8 +68,9 @@ void siw_umem_release(struct siw_umem *umem, bool dirty) for (i = 0; num_pages; i++) { int to_free = min_t(int, PAGES_PER_CHUNK, num_pages); - siw_free_plist(&umem->page_chunk[i], to_free, - umem->writable && dirty); + put_user_pages_dirty_lock(umem->page_chunk[i].plist, + to_free, + umem->writable && dirty); kfree(umem->page_chunk[i].plist); num_pages -= to_free; } diff --git a/include/linux/mm.h b/include/linux/mm.h index 0334ca97c584..9759b6a24420 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -1057,8 +1057,9 @@ 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_dirty_lock(struct page **pages, unsigned long npages, + bool make_dirty); + void put_user_pages(struct page **pages, unsigned long npages); #if defined(CONFIG_SPARSEMEM) && !defined(CONFIG_SPARSEMEM_VMEMMAP) diff --git a/mm/gup.c b/mm/gup.c index 98f13ab37bac..7fefd7ab02c4 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -29,85 +29,70 @@ struct follow_page_context { unsigned int page_mask; }; -typedef int (*set_dirty_func_t)(struct page *page); - -static void __put_user_pages_dirty(struct page **pages, - unsigned long npages, - set_dirty_func_t sdf) -{ - unsigned long index; - - for (index = 0; index < npages; index++) { - struct page *page = compound_head(pages[index]); - - /* - * Checking PageDirty at this point may race with - * clear_page_dirty_for_io(), but that's OK. Two key cases: - * - * 1) This code sees the page as already dirty, so it skips - * the call to sdf(). That could happen because - * clear_page_dirty_for_io() called page_mkclean(), - * followed by set_page_dirty(). However, now the page is - * going to get written back, which meets the original - * intention of setting it dirty, so all is well: - * clear_page_dirty_for_io() goes on to call - * TestClearPageDirty(), and write the page back. - * - * 2) This code sees the page as clean, so it calls sdf(). - * The page stays dirty, despite being written back, so it - * gets written back again in the next writeback cycle. - * This is harmless. - */ - if (!PageDirty(page)) - sdf(page); - - put_user_page(page); - } -} - /** - * put_user_pages_dirty() - release and dirty an array of gup-pinned pages - * @pages: array of pages to be marked dirty and released. + * put_user_pages_dirty_lock() - release and optionally dirty gup-pinned pages + * @pages: array of pages to be maybe marked dirty, and definitely released. * @npages: number of pages in the @pages array. + * @make_dirty: whether to mark the pages dirty * * "gup-pinned page" refers to a page that has had one of the get_user_pages() * variants called on that page. * * 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(). + * compound page) dirty, if @make_dirty is true, and if the page was previously + * listed as clean. In any case, releases all pages using put_user_page(), + * possibly via put_user_pages(), for the non-dirty case. * * 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. + * set_page_dirty_lock() is used internally. If instead, set_page_dirty() is + * required, then the caller should a) verify that this is really correct, + * because _lock() is usually required, and b) hand code it: + * set_page_dirty_lock(), put_user_page(). * */ -void put_user_pages_dirty(struct page **pages, unsigned long npages) +void put_user_pages_dirty_lock(struct page **pages, unsigned long npages, + bool make_dirty) { - __put_user_pages_dirty(pages, npages, set_page_dirty); -} -EXPORT_SYMBOL(put_user_pages_dirty); + unsigned long index; -/** - * put_user_pages_dirty_lock() - release and dirty an array of gup-pinned pages - * @pages: array of pages to be marked dirty and released. - * @npages: number of pages in the @pages array. - * - * 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(). - * - */ -void put_user_pages_dirty_lock(struct page **pages, unsigned long npages) -{ - __put_user_pages_dirty(pages, npages, set_page_dirty_lock); + /* + * TODO: this can be optimized for huge pages: if a series of pages is + * physically contiguous and part of the same compound page, then a + * single operation to the head page should suffice. + */ + + if (!make_dirty) { + put_user_pages(pages, npages); + return; + } + + for (index = 0; index < npages; index++) { + struct page *page = compound_head(pages[index]); + /* + * Checking PageDirty at this point may race with + * clear_page_dirty_for_io(), but that's OK. Two key + * cases: + * + * 1) This code sees the page as already dirty, so it + * skips the call to set_page_dirty(). That could happen + * because clear_page_dirty_for_io() called + * page_mkclean(), followed by set_page_dirty(). + * However, now the page is going to get written back, + * which meets the original intention of setting it + * dirty, so all is well: clear_page_dirty_for_io() goes + * on to call TestClearPageDirty(), and write the page + * back. + * + * 2) This code sees the page as clean, so it calls + * set_page_dirty(). The page stays dirty, despite being + * written back, so it gets written back again in the + * next writeback cycle. This is harmless. + */ + if (!PageDirty(page)) + set_page_dirty_lock(page); + put_user_page(page); + } } EXPORT_SYMBOL(put_user_pages_dirty_lock);