Re: [PATCH 03/13] scatterlist: Add sg_set_folio()

[Zhu Yanjun]

在 2023/7/31 5:42, Matthew Wilcox 写道:
> On Sun, Jul 30, 2023 at 09:57:06PM +0800, Zhu Yanjun wrote:
> > 在 2023/7/30 19:18, Matthew Wilcox 写道:
> > > On Sun, Jul 30, 2023 at 07:01:26PM +0800, Zhu Yanjun wrote:
> > > > Does the following function have folio version?
> > > >
> > > > "
> > > > int sg_alloc_append_table_from_pages(struct sg_append_table *sgt_append,
> > > > 		struct page **pages, unsigned int n_pages, unsigned int offset,
> > > > 		unsigned long size, unsigned int max_segment,
> > > > 		unsigned int left_pages, gfp_t gfp_mask)
> > > > "
> > > No -- I haven't needed to convert anything that uses
> > > sg_alloc_append_table_from_pages() yet.  It doesn't look like it should
> > > be _too_ hard to add a folio version.
> > In many places, this function is used. So this function needs the folio
> > version.
> It's not used in very many places.  But the first one that I see it used
> (drivers/infiniband/core/umem.c), you can't do a straightforward folio
> conversion:
>
>                  pinned = pin_user_pages_fast(cur_base,
>                                            min_t(unsigned long, npages,
>                                                  PAGE_SIZE /
>                                                  sizeof(struct page *)),
>                                            gup_flags, page_list);
> ...
>                  ret = sg_alloc_append_table_from_pages(
>                          &umem->sgt_append, page_list, pinned, 0,
>                          pinned << PAGE_SHIFT, ib_dma_max_seg_size(device),
>                          npages, GFP_KERNEL);
>
> That can't be converted to folios.  The GUP might start in the middle of
> the folio, and we have no way to communicate that.
>
> This particular usage really needs the phyr work that Jason is doing so
> we can efficiently communicate physically contiguous ranges from GUP
> to sg.

Hi, Matthew

Thanks. To the following function, it seems that no folio function 
replace vmalloc_to_page.

vmalloc_to_page calls virt_to_page to get page. Finally the followings 
will be called.

"
(mem_map + ((pfn) - ARCH_PFN_OFFSET))

"

And I do not find the related folio functions with vmalloc_to_page.

And no folio function replaces dma_map_page.

dma_map_page will call dma_map_page_attrs.

Or these 2 function should not be replaced with folio functions?

int irdma_map_vm_page_list(struct irdma_hw *hw, void *va, dma_addr_t 
*pg_dma,

                           u32 pg_cnt)
{
        struct page *vm_page;
        int i;
        u8 *addr;

        addr = (u8 *)(uintptr_t)va;
        for (i = 0; i < pg_cnt; i++) {
                vm_page = vmalloc_to_page(addr);
                if (!vm_page)
                        goto err;

                pg_dma[i] = dma_map_page(hw->device, vm_page, 0, PAGE_SIZE,
                                         DMA_BIDIRECTIONAL);
                if (dma_mapping_error(hw->device, pg_dma[i]))
                        goto err;

                addr += PAGE_SIZE;
        }

        return 0;

err:
        irdma_unmap_vm_page_list(hw, pg_dma, i);
        return -ENOMEM;

}

Thanks,

Zhu Yanjun


> > Another problem, after folio is used, I want to know the performance after
> > folio is implemented.
> >
> > How to make tests to get the performance?
> You know what you're working on ... I wouldn't know how best to test
> your code.