Date: Fri, 12 Jan 2018 10:48:21 -0800
From: Matthew Wilcox <willy@infradead.org>
To: Laurent Dufour <ldufour@linux.vnet.ibm.com>
Cc: paulmck@linux.vnet.ibm.com, peterz@infradead.org,
        akpm@linux-foundation.org, kirill@shutemov.name,
        ak@linux.intel.com, mhocko@kernel.org, dave@stgolabs.net,
        jack@suse.cz, benh@kernel.crashing.org, mpe@ellerman.id.au,
        paulus@samba.org, Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, hpa@zytor.com,
        Will Deacon <will.deacon@arm.com>,
        Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Alexei Starovoitov <alexei.starovoitov@gmail.com>,
        kemi.wang@intel.com, sergey.senozhatsky.work@gmail.com,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        haren@linux.vnet.ibm.com, khandual@linux.vnet.ibm.com,
        npiggin@gmail.com, bsingharora@gmail.com,
        Tim Chen <tim.c.chen@linux.intel.com>,
        linuxppc-dev@lists.ozlabs.org, x86@kernel.org
Subject: Re: [PATCH v6 16/24] mm: Protect mm_rb tree with a rwlock
Message-ID: <20180112184821.GB7590@bombadil.infradead.org>
References: <1515777968-867-1-git-send-email-ldufour@linux.vnet.ibm.com>
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On Fri, Jan 12, 2018 at 06:26:00PM +0100, Laurent Dufour wrote:
> -static void __vma_rb_erase(struct vm_area_struct *vma, struct rb_root *root)
> +static void __vma_rb_erase(struct vm_area_struct *vma, struct mm_struct *mm)
>  {
> +	struct rb_root *root = &mm->mm_rb;
>  	/*
>  	 * Note rb_erase_augmented is a fairly large inline function,
>  	 * so make sure we instantiate it only once with our desired
>  	 * augmented rbtree callbacks.
>  	 */
> +#ifdef CONFIG_SPF
> +	write_lock(&mm->mm_rb_lock);
> +#endif
>  	rb_erase_augmented(&vma->vm_rb, root, &vma_gap_callbacks);
> +#ifdef CONFIG_SPF
> +	write_unlock(&mm->mm_rb_lock); /* wmb */
> +#endif

I can't say I love this.  Have you considered:

#ifdef CONFIG_SPF
#define vma_rb_write_lock(mm)	write_lock(&mm->mm_rb_lock)
#define vma_rb_write_unlock(mm)	write_unlock(&mm->mm_rb_lock)
#else
#define vma_rb_write_lock(mm)	do { } while (0)
#define vma_rb_write_unlock(mm)	do { } while (0)
#endif

Also, SPF is kind of uninformative.  CONFIG_MM_SPF might be better?
Or perhaps even CONFIG_SPECULATIVE_PAGE_FAULT, just to make it really
painful to do these one-liner ifdefs that make the code so hard to read.