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Date: Mon, 08 Apr 2013 11:46:42 -0700
From: Dave Hansen <dave@sr71.net>
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Subject: Re: [PATCHv3, RFC 31/34] thp: initial implementation of do_huge_linear_fault()
References: <1365163198-29726-1-git-send-email-kirill.shutemov@linux.intel.com> <1365163198-29726-32-git-send-email-kirill.shutemov@linux.intel.com>
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To: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>, Andrew Morton <akpm@linux-foundation.org>, Al Viro <viro@zeniv.linux.org.uk>, Hugh Dickins <hughd@google.com>, Wu Fengguang <fengguang.wu@intel.com>, Jan Kara <jack@suse.cz>, Mel Gorman <mgorman@suse.de>, linux-mm@kvack.org, Andi Kleen <ak@linux.intel.com>, Matthew Wilcox <matthew.r.wilcox@intel.com>, "Kirill A. Shutemov" <kirill@shutemov.name>, Hillf Danton <dhillf@gmail.com>, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org

On 04/05/2013 04:59 AM, Kirill A. Shutemov wrote:
> +	if (unlikely(khugepaged_enter(vma)))
> +		return VM_FAULT_OOM;
...
> +	ret = vma->vm_ops->huge_fault(vma, &vmf);
> +	if (unlikely(ret & VM_FAULT_OOM))
> +		goto uncharge_out_fallback;
> +	if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | VM_FAULT_RETRY)))
> +		goto uncharge_out;
> +
> +	if (unlikely(PageHWPoison(vmf.page))) {
> +		if (ret & VM_FAULT_LOCKED)
> +			unlock_page(vmf.page);
> +		ret = VM_FAULT_HWPOISON;
> +		goto uncharge_out;
> +	}

One note on all these patches, but especially this one is that I think
they're way too liberal with unlikely()s.  You really don't need to do
this for every single error case.  Please reserve them for places where
you _know_ there is a benefit, or that the compiler is doing things that
you _know_ are blatantly wrong.

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