linux-kernel - Re: [PATCH v4 0/7] HWpoison: further fixes and cleanups

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Message-ID: <da0a0c702d944e98dd690349947c0fe5@suse.de>
Date:   Fri, 18 Sep 2020 07:49:11 +0200
From:   osalvador@...e.de
To:     HORIGUCHI NAOYA(堀口　直也) <naoya.horiguchi@....com>
Cc:     akpm@...ux-foundation.org, aris@...vo.org, mhocko@...nel.org,
        tony.luck@...el.com, cai@....pw, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [PATCH v4 0/7] HWpoison: further fixes and cleanups

On 2020-09-17 17:27, HORIGUCHI NAOYA wrote:
> Sorry, I modified the patches based on the different assumption from 
> yours.
> I firstly thought of taking page off after confirming the error page
> is freed back to buddy. This approach leaves the possibility of reusing
> the error page (which is acceptable), but simpler and less invasive 
> one.
> 
> Your approach removes the error page from page allocator's control in
> freeing time. It has no possibility of reusing the error page but 
> changes
> are tightly coupled with page free code.
> 
> This is a tradeoff between complexity and completeness of soft offline,
> Now I'm not sure I could persist on my own opinion without providing
> working code, and it's OK for me to take your one.

Yeah, you are right it is a trade off.
I would suggest taking this path now, and if it proofs to be problematic 
in some way, we can always
do the:

free_page
  take_it_off_buddy
   OK: mark it as hwpoison and increment refcount
   NOT_OK (raced with allocation): oops, sorry

> The test passed in my environment, so this is fine.

Thanks for trying it out.

> 
>> If they do, I will try to see if Andrew can squezee above changes into 
>> [1],
>> where they belong to.
> 
> Yes, proposing the fix for 
> mmhwpoison-rework-soft-offline-for-in-use-pages.patch
> seems fine to me.
> 
> Again, sorry for modifying code without asking.

No worries, I wil do a couple of tests on my own and then I will talk to 
Andrew to see if we can squeeze the changes in there.