linux-kernel - Re: [PATCH 1/3] mm: Allow anon exclusive check over hugetlb tail pages

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Date: Thu, 4 Apr 2024 15:06:25 +0100
From: Matthew Wilcox <willy@...radead.org>
To: Peter Xu <peterx@...hat.com>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Huacai Chen <chenhuacai@...nel.org>,
	David Hildenbrand <david@...hat.com>,
	Jason Gunthorpe <jgg@...dia.com>,
	Nathan Chancellor <nathan@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	WANG Xuerui <kernel@...0n.name>,
	Ryan Roberts <ryan.roberts@....com>, loongarch@...ts.linux.dev
Subject: Re: [PATCH 1/3] mm: Allow anon exclusive check over hugetlb tail
 pages

On Thu, Apr 04, 2024 at 09:45:58AM -0400, Peter Xu wrote:
> On Thu, Apr 04, 2024 at 01:05:57AM +0100, Matthew Wilcox wrote:
> > 	if (PageHuge(page))
> > 		page = compound_head(page);
> 
> I would think PageHead() check would help us to avoid compound_head() on
> heads, which should still be the majority cases iiuc (assuming page->flags
> is already around in the cache anyway).  I've no strong opinion though, as
> I can hardly tell a difference in reality.

compound_head() includes a check for PageHead().  Adding the check just
makes things slower.