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

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Message-ID: <20170830055800.GG32112@worktop.programming.kicks-ass.net>
Date:   Wed, 30 Aug 2017 07:58:00 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Anshuman Khandual <khandual@...ux.vnet.ibm.com>
Cc:     Laurent Dufour <ldufour@...ux.vnet.ibm.com>,
        "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 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.

> @@ -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.