linux-kernel - Re: [PATCHv3, RFC 31/34] thp: initial implementation of do_huge_linear

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Date:	Mon, 08 Apr 2013 11:46:42 -0700
From:	Dave Hansen <dave@...1.net>
To:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
CC:	Andrea Arcangeli <aarcange@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Hugh Dickins <hughd@...gle.com>,
	Wu Fengguang <fengguang.wu@...el.com>, Jan Kara <jack@...e.cz>,
	Mel Gorman <mgorman@...e.de>, linux-mm@...ck.org,
	Andi Kleen <ak@...ux.intel.com>,
	Matthew Wilcox <matthew.r.wilcox@...el.com>,
	"Kirill A. Shutemov" <kirill@...temov.name>,
	Hillf Danton <dhillf@...il.com>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCHv3, RFC 31/34] thp: initial implementation of do_huge_linear_fault()

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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