linux-kernel - Re: [PATCH 1/2] mm/page_alloc.c: cleanup obsolete KM

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Message-ID: <CALUN=qJheGR9ahrikS5Mith25gz6KmTML-NDB=cfpQmsotN0Lw@mail.gmail.com>
Date:	Sat, 25 Apr 2015 15:43:18 +0200
From:	Anisse Astier <anisse@...ier.eu>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Alan Cox <gnomes@...rguk.ukuu.org.uk>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	PaX Team <pageexec@...email.hu>,
	Brad Spengler <spender@...ecurity.net>,
	Kees Cook <keescook@...omium.org>, linux-mm@...ck.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] mm/page_alloc.c: cleanup obsolete KM_USER*

Hi David,

First of all, thanks a lot for your time reviewing this series.

On Fri, Apr 24, 2015 at 11:36 PM, David Rientjes <rientjes@...gle.com> wrote:
> On Fri, 24 Apr 2015, Anisse Astier wrote:
>
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index ebffa0e..05fcec9 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -380,16 +380,10 @@ void prep_compound_page(struct page *page, unsigned long order)
>>       }
>>  }
>>
>> -static inline void prep_zero_page(struct page *page, unsigned int order,
>> -                                                     gfp_t gfp_flags)
>> +static inline void zero_pages(struct page *page, unsigned int order)
>>  {
>>       int i;
>>
>> -     /*
>> -      * clear_highpage() will use KM_USER0, so it's a bug to use __GFP_ZERO
>> -      * and __GFP_HIGHMEM from hard or soft interrupt context.
>> -      */
>> -     VM_BUG_ON((gfp_flags & __GFP_HIGHMEM) && in_interrupt());
>>       for (i = 0; i < (1 << order); i++)
>>               clear_highpage(page + i);
>>  }
>> @@ -975,7 +969,7 @@ static int prep_new_page(struct page *page, unsigned int order, gfp_t gfp_flags,
>>       kasan_alloc_pages(page, order);
>>
>>       if (gfp_flags & __GFP_ZERO)
>> -             prep_zero_page(page, order, gfp_flags);
>> +             zero_pages(page, order);
>>
>>       if (order && (gfp_flags & __GFP_COMP))
>>               prep_compound_page(page, order);
>
> No objection to removing the VM_BUG_ON() here, but I'm not sure that we
> need an inline function to do this and to add additional callers in your
> next patch.  Why can't we just remove the helper entirely and do the
> iteration in prep_new_page()?  We iterate pages all the time.

I just felt it was easier to read as a whole; unless anyone else
objects, I think I'll keep it as-is in the next iteration.

Anisse
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