RE: [PATCH] Fix incorrect compound page flags store

["yaoaili [么爱利]" <yaoaili@kingsoft.com>]

Hi
I think if the poision page is from patrol scrub, the page may be a just compound page in driver(not huge and transhuge), which it's ok for the following hwpoison_user_mappings. For  PageTransHuge, we have split it, the the flags will be good.
so I think the modification in the latest mmotm  is OK
-----Original Message-----
From: Oscar Salvador [mailto:osalvador@suse.de] 
Sent: Tuesday, September 8, 2020 3:26 PM
To: HORIGUCHI NAOYA(堀口　直也) <naoya.horiguchi@nec.com>
Cc: yaoaili126@163.com; linux-mm@kvack.org; YANGFENG1 [杨峰] <YANGFENG1@kingsoft.com>; yaoaili [么爱利] <yaoaili@kingsoft.com>; willy@infradead.org
Subject: Re: [PATCH] Fix incorrect compound page flags store

On Tue, Sep 08, 2020 at 07:02:12AM +0000, HORIGUCHI NAOYA(堀口 直也) wrote:
> On Mon, Sep 07, 2020 at 08:44:42PM -0700, yaoaili126@163.com wrote:
> > From: Aili Yao <yaoaili@kingsoft.com>
> > 
> > PageHuge(p) branch will never be true,but for compound page we need to set page_flags to correct value.
> > 
> > Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> > Signed-off-by: Yang Feng < yangfeng1@kingsoft.com>
> > Signed-off-by: Aili Yao <yaoaili@kingsoft.com>
> 
> I found that this PageHuge() check is removed and no long exists in 
> the latest mmotm, so we don't have worry about it.

I might be missing something, so bear with me.

It is true that the PageHuge check is gone, but we are storing the page's flags in page_flags, even if the page is a tail (e.g: part of a compound page ).
Should not we store heads' flags instead?

AFAICS, hpage contains either the head of the compound page, or the page itself in case it is a normal page.

--
Oscar Salvador
SUSE L3