linux-kernel - Re: [RFC v3 03/17] mm: Introduce pte

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Message-Id: <1b334821-1929-38ed-5316-2a7d135b812d@linux.vnet.ibm.com>
Date:   Wed, 3 May 2017 15:01:14 +0200
From:   Laurent Dufour <ldufour@...ux.vnet.ibm.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     paulmck@...ux.vnet.ibm.com, peterz@...radead.org,
        akpm@...ux-foundation.org, kirill@...temov.name,
        ak@...ux.intel.com, mhocko@...nel.org, dave@...olabs.net,
        jack@...e.cz, linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        haren@...ux.vnet.ibm.com, khandual@...ux.vnet.ibm.com,
        npiggin@...il.com, bsingharora@...il.com
Subject: Re: [RFC v3 03/17] mm: Introduce pte_spinlock

On 30/04/2017 06:47, Matthew Wilcox wrote:
> On Thu, Apr 27, 2017 at 05:52:42PM +0200, Laurent Dufour wrote:
>> +++ b/mm/memory.c
>> @@ -2100,6 +2100,13 @@ static inline void wp_page_reuse(struct vm_fault *vmf)
>>  	pte_unmap_unlock(vmf->pte, vmf->ptl);
>>  }
>>  
>> +static bool pte_spinlock(struct vm_fault *vmf)
>> +{
>> +	vmf->ptl = pte_lockptr(vmf->vma->vm_mm, vmf->pmd);
>> +	spin_lock(vmf->ptl);
>> +	return true;
>> +}
> 
> To me 'pte_spinlock' is a noun, but this is really pte_spin_lock() (a verb).

Fair enough. Even pte_trylock() should be more accurate since patch 8/17
changes this function to call spin_trylock().

> Actually, it's really vmf_lock_pte().  We're locking the pte
> referred to by this vmf.  And so we should probably have a matching
> vmf_unlock_pte(vmf) to preserve the abstraction.

I'm not sure this will ease the reading. In most of this code, the pte
are unlocked through the call to pte_unmap_unlock().
The call to pte_trylock() has been introduced because in few cases there
is the need to check the VMA validity before calling spinlock(ptl). The
unlock is then managed through pte_unmap_unlock().