[PATCH v2 1/4] net: introduce helper sendpages_ok()

[Sagi Grimberg]

>> I still don't understand how a page in the middle of a contiguous range ends
>> up coming from the slab while others don't.
> I haven't investigate the origin of the IO
> yet. I suspect the first 2 pages are the superblocks of the raid
> (mdp_superblock_1 and bitmap_super_s) and the rest of the IO is the bitmap.

Well, if these indeed are different origins and just *happen* to be a 
mixture
of slab originated pages and non-slab pages combined together in a 
single bio of a bvec entry,
I'd suspect that it would be more beneficial to split the bvec 
(essentially not allow bio_add_page
to append the page to tail bvec depending on a queue limit (similar to 
how we handle sg gaps).

>
>> Ofir, can you please check which condition in sendpage_ok actually fails?
> It failed because the page has slab, page count is 1. Sorry for not
> clarifying this.
>
> "skbuff: !sendpage_ok - page: 0x54f9f140 (pfn: 120757). is_slab: 1, page_count: 1"
>                                                                   ^
> The print I used:
> pr_info(
>      "!sendpage_ok - page: 0x%p (pfn: %lx). is_slab: %u, page_count: %u\n",
>      (void *)page,
>      page_to_pfn(page),
>      page_address(page),
>      !!PageSlab(page),
>      page_count(page)
> );
>
>