Received-SPF: pass (google.com: domain of linux-kernel+bounces-131606-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:4601:e00::3 as permitted sender) client-ip=2604:1380:4601:e00::3;
Date: Thu, 4 Apr 2024 10:21:21 -0400
From: Peter Xu <peterx@redhat.com>
To: Matthew Wilcox <willy@infradead.org>,
	Andrew Morton <akpm@linux-foundation.org>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	Huacai Chen <chenhuacai@kernel.org>,
	David Hildenbrand <david@redhat.com>,
	Jason Gunthorpe <jgg@nvidia.com>,
	Nathan Chancellor <nathan@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	WANG Xuerui <kernel@xen0n.name>,
	Ryan Roberts <ryan.roberts@arm.com>, loongarch@lists.linux.dev
Subject: Re: [PATCH 1/3] mm: Allow anon exclusive check over hugetlb tail
 pages
Message-ID: <Zg63YZaXqYdSLHG-@x1n>
References: <20240403013249.1418299-1-peterx@redhat.com>
 <20240403013249.1418299-2-peterx@redhat.com>
 <Zg3u5Sh9EbbYPhaI@casper.infradead.org>
 <Zg6vFtciZAl4SQHW@x1n>
 <Zg6z4ZEt7rbILgl8@casper.infradead.org>
Precedence: bulk
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
In-Reply-To: <Zg6z4ZEt7rbILgl8@casper.infradead.org>

On Thu, Apr 04, 2024 at 03:06:25PM +0100, Matthew Wilcox wrote:
> 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.

They check different fields (compound_head, offset 0x8 for the former).
Again I'm ok with either way to go and I don't expect measurable
difference.. so if you prefer this I'm happy with it too.

Andrew, could you help update with Matthew's fixup?  The comment is
definitely better than what I wrote in all cases.

Thanks,

-- 
Peter Xu