Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Fri, 19 Feb 2021 11:14:32 +0100
From:   Oscar Salvador <osalvador@suse.de>
To:     Michal Hocko <mhocko@suse.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        David Hildenbrand <david@redhat.com>,
        Muchun Song <songmuchun@bytedance.com>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/2] mm: Make alloc_contig_range handle free hugetlb pages
Message-ID: <20210219101427.GA19588@linux>
References: <20210217100816.28860-1-osalvador@suse.de>
 <20210217100816.28860-2-osalvador@suse.de>
 <YC0ve4PP+VTrEEtw@dhcp22.suse.cz>
 <20210218100917.GA4842@localhost.localdomain>
 <YC5jFrwegRVkMkBQ@dhcp22.suse.cz>
 <20210218133250.GA7983@localhost.localdomain>
 <YC5yzNB9xT76fkod@dhcp22.suse.cz>
 <20210219090548.GA17266@linux>
 <YC+LWksScdiuPw7X@dhcp22.suse.cz>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <YC+LWksScdiuPw7X@dhcp22.suse.cz>
User-Agent: Mutt/1.10.1 (2018-07-13)
Precedence: bulk

On Fri, Feb 19, 2021 at 10:56:42AM +0100, Michal Hocko wrote:
> OK, this should work but I am really wondering whether it wouldn't be
> just simpler to replace the old page by a new one in the free list
> directly. Or is there any reason we have to go through the generic
> helpers path? I mean something like this
> 
> 	new_page = alloc_fresh_huge_page();
> 	if (!new_page)
> 		goto fail;
> 	spin_lock(hugetlb_lock);
> 	if (!PageHuge(old_page)) {
> 		/* freed from under us, nothing to do */ 
> 		__update_and_free_page(new_page);
> 		goto unlock;
> 	}
> 	list_del(&old_page->lru);
> 	__update_and_free_page(old_page);
> 	__enqueue_huge_page(new_page);
> unlock:
> 	spin_unlock(hugetlb_lock);
> 
> This will require to split update_and_free_page and enqueue_huge_page to
> counters independent parts but that shouldn't be a big deal. But it will
> also protect from any races. Not an act of beauty but seems less hackish
> to me.

Yes, I think this would to the trick, and it is race-free.
Let me play with it a bit and see what I can come up with.

Thanks for the valuable insight.

-- 
Oscar Salvador
SUSE L3