RE: [PATCH v3 1/2] mm: migration: fix the FOLL_GET failure on following huge page

[Wang, Haiyue]

> -----Original Message-----
> From: Huang, Ying <ying.huang@xxxxxxxxx>
> Sent: Monday, August 15, 2022 09:59
> To: Wang, Haiyue <haiyue.wang@xxxxxxxxx>
> Cc: linux-mm@xxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; akpm@xxxxxxxxxxxxxxxxxxxx; david@xxxxxxxxxx;
> linmiaohe@xxxxxxxxxx; songmuchun@xxxxxxxxxxxxx; naoya.horiguchi@xxxxxxxxx; alex.sierra@xxxxxxx
> Subject: Re: [PATCH v3 1/2] mm: migration: fix the FOLL_GET failure on following huge page
> 
> Haiyue Wang <haiyue.wang@xxxxxxxxx> writes:
> 
> > Not all huge page APIs support FOLL_GET option, so the __NR_move_pages
> 
> move_pages() is a syscall, so you can just call it move_pages(), or
> move_pages() syscall.

The application meets the issue, use the bellow function:
syscall (__NR_move_pages, 0, n_pages, ptr, 0, status, 0)

So I used it directly in the commit. "move_pages() syscall" is better.
Will update latter.

> 
> > will fail to get the page node information for huge page.
>                                                  ~~~~~~~~~
> some huge pages?

OK.

> 
> > This is an temporary solution to mitigate the racing fix.
> 
> Why is it "racing fix"?  This isn't a race condition fix.

The 'Fixes' commit is about race condition fix.

How about " his is an temporary solution to mitigate the side effect
Of the race condition fix"

> 
> Best Regards,
> Huang, Ying
> 
> > After supporting follow huge page by FOLL_GET is done, this fix can be
> > reverted safely.
> >
> > Fixes: 4cd614841c06 ("mm: migration: fix possible do_pages_stat_array racing with memory offline")
> > Signed-off-by: Haiyue Wang <haiyue.wang@xxxxxxxxx>
> 
> [snip]