netdev - Re: [PATCH 03/13] scatterlist: Add sg_set

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Message-ID: <a1ad6a41-edd0-1201-c537-68693d5b70e6@linux.dev>
Date: Fri, 18 Aug 2023 15:05:14 +0800
From: Zhu Yanjun <yanjun.zhu@...ux.dev>
To: Matthew Wilcox <willy@...radead.org>
Cc: linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
 dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
 intel-gfx@...ts.freedesktop.org, linux-afs@...ts.infradead.org,
 linux-nfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
 netdev@...r.kernel.org
Subject: Re: [PATCH 03/13] scatterlist: Add sg_set_folio()


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.