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From: Michal Hocko <mhocko@kernel.org>
To: Alexander Duyck <alexander.h.duyck@linux.intel.com>
Cc: linux-mm@kvack.org, akpm@linux-foundation.org,
	pavel.tatashin@microsoft.com, dave.jiang@intel.com,
	linux-kernel@vger.kernel.org, willy@infradead.org,
	davem@davemloft.net, yi.z.zhang@linux.intel.com,
	khalid.aziz@oracle.com, rppt@linux.vnet.ibm.com, vbabka@suse.cz,
	sparclinux@vger.kernel.org, dan.j.williams@intel.com,
	ldufour@linux.vnet.ibm.com, mgorman@techsingularity.net,
	mingo@kernel.org, kirill.shutemov@linux.intel.com
Subject: Re: [mm PATCH v3 1/6] mm: Use mm_zero_struct_page from SPARC on all 64b architectures
Date: Wed, 17 Oct 2018 18:34:11 +0200	[thread overview]
Message-ID: <20181017163411.GT18839@dhcp22.suse.cz> (raw)
In-Reply-To: <9700b00f-a8a4-e318-f6a8-71fd1e7021b3@linux.intel.com>

On Wed 17-10-18 08:07:06, Alexander Duyck wrote:
> On 10/17/2018 1:47 AM, Michal Hocko wrote:
> > On Mon 15-10-18 13:26:56, Alexander Duyck wrote:
[...]
> > > diff --git a/include/linux/mm.h b/include/linux/mm.h
> > > index bb0de406f8e7..ec6e57a0c14e 100644
> > > --- a/include/linux/mm.h
> > > +++ b/include/linux/mm.h
> > > @@ -102,8 +102,42 @@ static inline void set_max_mapnr(unsigned long limit) { }
> > >    * zeroing by defining this macro in <asm/pgtable.h>.
> > >    */
> > >   #ifndef mm_zero_struct_page
> > 
> > Do we still need this ifdef? I guess we can wait for an arch which
> > doesn't like this change and then add the override. I would rather go
> > simple if possible.
> 
> We probably don't, but as soon as I remove it somebody will probably
> complain somewhere. I guess I could drop it for now and see if anybody
> screams. Adding it back should be pretty straight forward since it would
> only be 2 lines.

Let's make it simpler please. If somebody really cares then this is
trivial to add later.
 
> > > +#if BITS_PER_LONG == 64
> > > +/* This function must be updated when the size of struct page grows above 80
> > > + * or reduces below 64. The idea that compiler optimizes out switch()
> > > + * statement, and only leaves move/store instructions
> > > + */
> > > +#define	mm_zero_struct_page(pp) __mm_zero_struct_page(pp)
> > > +static inline void __mm_zero_struct_page(struct page *page)
> > > +{
> > > +	unsigned long *_pp = (void *)page;
> > > +
> > > +	 /* Check that struct page is either 56, 64, 72, or 80 bytes */
> > > +	BUILD_BUG_ON(sizeof(struct page) & 7);
> > > +	BUILD_BUG_ON(sizeof(struct page) < 56);
> > > +	BUILD_BUG_ON(sizeof(struct page) > 80);
> > > +
> > > +	switch (sizeof(struct page)) {
> > > +	case 80:
> > > +		_pp[9] = 0;	/* fallthrough */
> > > +	case 72:
> > > +		_pp[8] = 0;	/* fallthrough */
> > > +	default:
> > > +		_pp[7] = 0;	/* fallthrough */
> > > +	case 56:
> > > +		_pp[6] = 0;
> > > +		_pp[5] = 0;
> > > +		_pp[4] = 0;
> > > +		_pp[3] = 0;
> > > +		_pp[2] = 0;
> > > +		_pp[1] = 0;
> > > +		_pp[0] = 0;
> > > +	}
> > 
> > This just hit my eyes. I have to confess I have never seen default: to
> > be not the last one in the switch. Can we have case 64 instead or does gcc
> > complain? I would be surprised with the set of BUILD_BUG_ONs.
> 
> I can probably just replace the "default:" with "case 64:". I think I have
> seen other switch statements in the kernel without a default so odds are it
> should be okay.

Please do, there shouldn't be any need to obfuscate the code more than
necessary.

-- 
Michal Hocko
SUSE Labs

  parent reply	other threads:[~2018-10-17 16:34 UTC|newest]

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-10-15 20:26 [mm PATCH v3 0/6] Deferred page init improvements Alexander Duyck
2018-10-15 20:26 ` [mm PATCH v3 1/6] mm: Use mm_zero_struct_page from SPARC on all 64b architectures Alexander Duyck
2018-10-16 19:01   ` Pavel Tatashin
2018-10-17  7:30     ` Mike Rapoport
2018-10-17 14:52       ` Alexander Duyck
2018-10-17  8:47   ` Michal Hocko
2018-10-17 15:07     ` Alexander Duyck
2018-10-17 15:12       ` Pavel Tatashin
2018-10-17 15:40         ` David Laight
2018-10-17 16:31           ` Alexander Duyck
2018-10-17 17:08             ` Pavel Tatashin
2018-10-17 16:34       ` Michal Hocko [this message]
2018-10-15 20:27 ` [mm PATCH v3 2/6] mm: Drop meminit_pfn_in_nid as it is redundant Alexander Duyck
2018-10-16 20:33   ` Pavel Tatashin
2018-10-16 20:49     ` Alexander Duyck
2018-10-16 21:06       ` Pavel Tatashin
2018-10-17  9:04   ` Michal Hocko
2018-10-15 20:27 ` [mm PATCH v3 3/6] mm: Use memblock/zone specific iterator for handling deferred page init Alexander Duyck
2018-10-17  9:11   ` Michal Hocko
2018-10-17 15:17     ` Alexander Duyck
2018-10-17 16:42   ` Mike Rapoport
2018-10-15 20:27 ` [mm PATCH v3 4/6] mm: Move hot-plug specific memory init into separate functions and optimize Alexander Duyck
2018-10-17  9:18   ` Michal Hocko
2018-10-17 15:26     ` Alexander Duyck
2018-10-24 12:36       ` Michal Hocko
2018-10-24 15:08         ` Alexander Duyck
2018-10-24 15:27           ` Michal Hocko
2018-10-24 17:35             ` Alexander Duyck
2018-10-25 12:41               ` Michal Hocko
2018-10-15 20:27 ` [mm PATCH v3 5/6] mm: Use common iterator for deferred_init_pages and deferred_free_pages Alexander Duyck
2018-10-15 20:27 ` [mm PATCH v3 6/6] mm: Add reserved flag setting to set_page_links Alexander Duyck

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