linux-kernel - Re: [Patch v2 4/4] mm/page_alloc.c: extract commom part to check page

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Date:   Tue, 21 Jan 2020 10:19:38 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     Wei Yang <richardw.yang@...ux.intel.com>
Cc:     akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, rientjes@...gle.com
Subject: Re: [Patch v2 4/4] mm/page_alloc.c: extract commom part to check page



On 01/20/2020 06:06 PM, Wei Yang wrote:
> On Mon, Jan 20, 2020 at 12:13:38PM +0530, Anshuman Khandual wrote:
>>
>>
>> On 01/20/2020 08:34 AM, Wei Yang wrote:
>>> During free and new page, we did some check on the status of page
>>> struct. There is some common part, just extract them.
>>
>> Makes sense.
>>
>>>
>>> Besides this, this patch also rename two functions to keep the name
>>> convention, since free_pages_check_bad/free_pages_check are counterparts
>>> of check_new_page_bad/check_new_page.
>>
>> This probably should be in a different patch.
>>
> 
> In v1, they are in two separate patches. While David Suggest to merge it.
> 
> I am not sure whether my understanding is correct.

Keeping code refactoring and renaming separate is always better
but its okay, will leave it upto you.

> 
>>>
>>> Signed-off-by: Wei Yang <richardw.yang@...ux.intel.com>
>>> ---
>>>  mm/page_alloc.c | 49 ++++++++++++++++++++++++-------------------------
>>>  1 file changed, 24 insertions(+), 25 deletions(-)
>>>
>>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>>> index a7b793c739fc..7f23cc836f90 100644
>>> --- a/mm/page_alloc.c
>>> +++ b/mm/page_alloc.c
>>> @@ -1025,36 +1025,44 @@ static inline bool page_expected_state(struct page *page,
>>>  	return true;
>>>  }
>>>  
>>> -static void free_pages_check_bad(struct page *page)
>>> +static inline int __check_page(struct page *page, int nr,
>>> +				const char **bad_reason)
>>
>> free and new page checks are in and out of the buddy allocator, hence
>> this common factored function should have a more relevant name.
> 
> Hmm... naming is really difficult. Do you have any suggestion?
> 

Probably something like bad_page_fetch_reasons() and also this helper
can be expanded to include an additional argument 'bool free' which
can test either PAGE_FLAGS_CHECK_AT_FREE or PAGE_FLAGS_CHECK_AT_PREP.
This way bad_page_fetch_reasons() is where all possible reasons are
evaluated including page->flags based and then final 'int nr' can be
returned once and for all.

bad_flags does not seem to be needed. Wondering what it adds more
in bad_page() when page->flags gets printed universally through
__dump_page(). In case it is still required, it can be derived
from 'bad_reasons' evaluated in bad_page_fetch_reasons().