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Re: [PATCH v2 2/2] dma-buf: heaps: Clear CMA highages using helper

by T.J. Mercier

On Tue, Mar 10, 2026 at 1:53 AM Linus Walleij <linusw(a)kernel.org> wrote: > > Currently the CMA allocator clears highmem pages using > kmap()->clear_page()->kunmap(), but there is a helper > static inline in <linux/highmem.h> that does the same for > us so use clear_highpage() instead of open coding this. > > Suggested-by: T.J. Mercier <tjmercier(a)google.com> > Signed-off-by: Linus Walleij <linusw(a)kernel.org> Reviewed-by: T.J. Mercier <tjmercier(a)google.com> Thanks!

1 week, 2 days

Re: [PATCH v2 0/2] dma-buf: heaps: Use page clearing helpers

by Maxime Ripard

On Tue, 10 Mar 2026 09:53:10 +0100, Linus Walleij wrote: > Use clear_pages() and clear_highpage() properly in the > DMA heap allocator. > > Signed-off-by: Linus Walleij <linusw(a)kernel.org> Reviewed-by: Maxime Ripard <mripard(a)kernel.org> Thanks! Maxime

1 week, 2 days

Re: [PATCH] lib/scatterlist: fix sg_page_count and sg_dma_page_count

by Jason Gunthorpe

On Tue, Mar 10, 2026 at 05:49:23AM +0000, Kasireddy, Vivek wrote: > There are a couple of reasons why we got rid of the pages array: > - Back then, there was some confusion about whether a struct page would > exist or not for tail pages when HVO is enabled. Regardless, there was also > a concern about exposing tail pages outside hugetlb code. The existing code relies on struct page for the vmap: for (pg = 0; pg < ubuf->pagecount; pg++) pages[pg] = folio_page(ubuf->folios[pg], ubuf->offsets[pg] >> PAGE_SHIFT); Tail pages always exist, they are required by many interfaces. > - And, we also wanted to prepare for a future where struct page would not > exist anymore, so, it made sense to just use folios only. If you can 100% stick with whole folios then great, but we don't have the APIs for that cases udmabuf needs right now. Most likely we'd expect to use phys_addr_t for scatterlist and direct full folio for vmap. Neither is helped by the datastructure in udmabuf. Jason

1 week, 2 days

Re: [PATCH v2 2/2] dma-buf: heaps: Clear CMA highages using helper

by Christian König

On 3/10/26 09:53, Linus Walleij wrote: > Currently the CMA allocator clears highmem pages using > kmap()->clear_page()->kunmap(), but there is a helper > static inline in <linux/highmem.h> that does the same for > us so use clear_highpage() instead of open coding this. > > Suggested-by: T.J. Mercier <tjmercier(a)google.com> > Signed-off-by: Linus Walleij <linusw(a)kernel.org> Ah yes, somebody pointed that out to me before but I never found time to write a patch to clean it up. Reviewed-by: Christian König <christian.koenig(a)amd.com> > --- > drivers/dma-buf/heaps/cma_heap.c | 5 +---- > 1 file changed, 1 insertion(+), 4 deletions(-) > > diff --git a/drivers/dma-buf/heaps/cma_heap.c b/drivers/dma-buf/heaps/cma_heap.c > index f0bacf25ed9d..92865786cfc9 100644 > --- a/drivers/dma-buf/heaps/cma_heap.c > +++ b/drivers/dma-buf/heaps/cma_heap.c > @@ -329,10 +329,7 @@ static struct dma_buf *cma_heap_allocate(struct dma_heap *heap, > struct page *page = cma_pages; > > while (nr_clear_pages > 0) { > - void *vaddr = kmap_local_page(page); > - > - clear_page(vaddr); > - kunmap_local(vaddr); > + clear_highpage(page); > /* > * Avoid wasting time zeroing memory if the process > * has been killed by SIGKILL. > > -- > 2.53.0 >

1 week, 2 days

Re: [PATCH] dma-buf: heaps: Clear CMA pages with clear_pages()

by T.J. Mercier

On Tue, Mar 3, 2026 at 4:25 PM Linus Walleij <linusw(a)kernel.org> wrote: > > As of commit 62a9f5a85b98 > "mm: introduce clear_pages() and clear_user_pages()" we can > clear a range of pages with a potentially assembly-optimized > call. > > Instead of using a memset, use this helper to clear the whole > range of pages from the CMA allocation. > > Signed-off-by: Linus Walleij <linusw(a)kernel.org> > --- > drivers/dma-buf/heaps/cma_heap.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/dma-buf/heaps/cma_heap.c b/drivers/dma-buf/heaps/cma_heap.c > index bd3370b9a3f6..f0bacf25ed9d 100644 > --- a/drivers/dma-buf/heaps/cma_heap.c > +++ b/drivers/dma-buf/heaps/cma_heap.c > @@ -343,7 +343,7 @@ static struct dma_buf *cma_heap_allocate(struct dma_heap *heap, > nr_clear_pages--; > } > } else { > - memset(page_address(cma_pages), 0, size); > + clear_pages(page_address(cma_pages), pagecount); > } > > buffer->pages = kmalloc_objs(*buffer->pages, pagecount); > > --- > base-commit: 6de23f81a5e08be8fbf5e8d7e9febc72a5b5f27f > change-id: 20260303-cma-heap-clear-pages-540f3ac9f734 > > Best regards, > -- > Linus Walleij <linusw(a)kernel.org> > Hi Linus, I think we can also use clear_highpage (singular) instead of memset in the while loop above here to be a little more concise. Thanks, T.J.

1 week, 2 days