linux-kernel - Re: [PATCH v2 14/20] mm: Provide speculative fault infrastructure

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Date:   Wed, 30 Aug 2017 11:32:42 +0200
From:   Laurent Dufour <ldufour@...ux.vnet.ibm.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Anshuman Khandual <khandual@...ux.vnet.ibm.com>
Cc:     "Kirill A. Shutemov" <kirill@...temov.name>,
        paulmck@...ux.vnet.ibm.com, akpm@...ux-foundation.org,
        ak@...ux.intel.com, mhocko@...nel.org, dave@...olabs.net,
        jack@...e.cz, Matthew Wilcox <willy@...radead.org>,
        benh@...nel.crashing.org, mpe@...erman.id.au, paulus@...ba.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, hpa@...or.com,
        Will Deacon <will.deacon@....com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        haren@...ux.vnet.ibm.com, npiggin@...il.com, bsingharora@...il.com,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        linuxppc-dev@...ts.ozlabs.org, x86@...nel.org
Subject: Re: [PATCH v2 14/20] mm: Provide speculative fault infrastructure

On 30/08/2017 07:58, Peter Zijlstra wrote:
> On Wed, Aug 30, 2017 at 10:33:50AM +0530, Anshuman Khandual wrote:
>> diff --git a/mm/filemap.c b/mm/filemap.c
>> index a497024..08f3042 100644
>> --- a/mm/filemap.c
>> +++ b/mm/filemap.c
>> @@ -1181,6 +1181,18 @@ int __lock_page_killable(struct page *__page)
>>  int __lock_page_or_retry(struct page *page, struct mm_struct *mm,
>>                          unsigned int flags)
>>  {
>> +       if (flags & FAULT_FLAG_SPECULATIVE) {
>> +               if (flags & FAULT_FLAG_KILLABLE) {
>> +                       int ret;
>> +
>> +                       ret = __lock_page_killable(page);
>> +                       if (ret)
>> +                               return 0;
>> +               } else
>> +                       __lock_page(page);
>> +               return 1;
>> +       }
>> +
>>         if (flags & FAULT_FLAG_ALLOW_RETRY) {
>>                 /*
>>                  * CAUTION! In this case, mmap_sem is not released
> 
> Yeah, that looks right.

Hum, I'm wondering if FAULT_FLAG_RETRY_NOWAIT should be forced in the
speculative path in that case to match the semantics of
__lock_page_or_retry().

> 
>> @@ -4012,17 +4010,7 @@ int handle_speculative_fault(struct mm_struct *mm, unsigned long address,
>>                 goto unlock;
>>         }
>>
>> +       if (unlikely(vma_is_anonymous(vma) && !vma->anon_vma)) {
>>                 trace_spf_vma_notsup(_RET_IP_, vma, address);
>>                 goto unlock;
>>         }
> 
> As riel pointed out on IRC slightly later, private file maps also need
> ->anon_vma and those actually have ->vm_ops IIRC so the condition needs
> to be slightly more complicated.

Yes I read again the code and lead to the same conclusion.